NCHurricane2009's Blog

2012 Atlantic Hurricane Season Birdseye Discussion #147

By: NCHurricane2009, 8:27 AM GMT on October 31, 2012

...WEDNESDAY OCTOBER 31 2012...4:27 AM EDT...
The remnant gale of Sandy over the northeastern United States has continued to weaken...with weather conditions improving except for in the Appalachian Mountains where blizzard and winter storm warnings remain in effect. See paragraph P1 of the mid-latitudes discussion for update statement on the remnant of Sandy.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...The remnant surface low of Sandy has orbited westward across southern Pennsylvania about the north side of the cut-off upper vortex previously to its southwest...and in turn low-level cool air wrapping around the west and south sides of Sandy has made the cold core upper vortex shift east then NE about Sandy's south side. Recently...the upper vortex and surface low have become vertically stacked such that the surface low of Sandy continues weakening beneath the non-divergent upper vortex. However...the Appalachian Mountains continue to be socked by snow and gusty winds...as the higher elevations are exposed to the portion of Sandy's circulation not limited by surface friction. Central US upper trough mentioned in paragraph P1 of the previous discussion will soon shift into the Great Lakes and pull Sandy and the upper vortex northward. Vast convergence west of this upper trough supports Gulf of Mexico and SW US surface ridging. Immense low-level warm air advection ahead of Sandy's large circulation continues supporting a large north Atlantic upper anticyclone. 1038 mb surface ridge on the east coast of Canada has weakened to an offshore 1031 mb ridge stacked below the upper anticyclone...and a surface ridge over Hudson Bay in Canada.

P2...Deep-layered low pressure system/upper vortex persists in the central Atlantic is shifting into the eastern Atlantic. At the surface...their continues to be a broad low pressure spin in the low 990s of mb that has whirled into a position beneath the upper vortex.

P3...Upper trough in the NE Atlantic persists in relatively lower pressures east of the the north Atlantic upper anticyclone in paragraph P1. Currently its eastern divergence supports a couple of surface frontal depressions near southern Spain along the warm front extending from the paragraph P2 deep-layered low.

...TROPICAL BELT DISCUSSION...
P4...Sprawling east-west tropical Atlantic upper anticyclone remains centered just NE of the Lesser Antilles. Upper divergence on the NW quad of the upper anticyclone continues supporting a surface trough extending from south of Sandy into the NW Caribbean...which has evolved into a cold front extending from Sandy..as well as continued surface troughing and new t-storms in the eastern Caribbean Sea. SW-retrograding upper vortex near the Cape Verde Islands in the previous discussion has opened into an upper trough W of the Cape Verde Islands while getting drawn into the south side of the paragraph P2 deep-layered low. Relatively higher pressures east of this upper trough supports a new upper ridge near the Cape Verde Islands.

P5...Surface troughing midway between the Cape Verde Islands and the Lesser Antilles has split into one surface trough heading toward the Lesser Antilles...and another surface trough becoming assimilated into the cold front extending from the paragraph P2 deep-layered cyclone. 1013 mb ridge west of the surface troughing and NE of the Lesser Antilles has strengthened to 1016 mb while taking advantage of upper convergence on the NE side of the paragraph P4 upper anticyclone. 1016 mb ridge to the east of the surface troughing and toward the Cape Verde Islands has weakened to 1012 mb due to upper divergence on the SE quad of the paragraph P2 deep-layered cyclone overspreading the area.

Updated: 8:28 AM GMT on October 31, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #146

By: NCHurricane2009, 5:58 AM GMT on October 30, 2012

...TUESDAY OCTOBER 30 2012...1:58 AM EDT...
Hurricane Sandy is living up to its expectation as one of the most damaging storms in United States History as it has transitioned into an intense and large-sized non-tropical gale. Statement on the epicenter of Sandy's impacts in New York City metro and New Jersey was written in special update #145A. Sandy's impacts are far from over...as she will slowly wind down thru the next 24 hours. See Figure 1 and additional statements in the Sandy special feature section for the impacts Sandy is to deliver over the next 24 hours.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1922Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...NON-TROPICAL GALE SANDY...
Track-wise for Sandy...see special update #145A for how the paragraph P1 upper vortex currently to the southwest of her became a bit more energized than previously thought. As a result...the upper vortex whirled Sandy into southern New Jersey a bit faster than previously thought. This upper vortex should continue ejecting east then eventually NE with cool air advection on the back and south sides of Sandy persisting...and I think Sandy should in turn loop cyclonically later today about the NW side of the NE ejecting upper vortex. But because the upper vortex is more energized than previously thought...I show Sandy flung by the upper vortex further west than my previous for 11 AM this morning...then making a larger radius loop just after. It should be noted that the NHC recorded storm track and NHC forecast are north of my solution for 11 AM this morning...but recently radar imagery shows Sandy turning westward such that her center should arrive in south-central Pennsylvania and hence toward my forecast track.

Because I show a larger radius loop than what I showed previously for Tuesday (today)...Sandy should be further east than I thought by the end of the loop...which makes my Wednesday and Thursday forecast points a bit more east than my previous. By Wednesday and Thursday...Sandy should be in a position to be lifted northward by paragraph P1 shortwave upper trough headed into the Great Lakes. I still expect Sandy's cool air advection to amplify this shortwave upper trough into a new upper vortex in the vicinity and to the south. Afterwards...this upper vortex should shoot NE...and so I have Sandy make another small cyclonic loop on Thursday around the west side of NE-shooting upper vortex. This NE shooting upper vortex's eastern divergence should create a new surface low by Friday located NE of Sandy...and I expect this new surface low's south side to pull Sandy ENE and absorb her.

Intensity-wise for Sandy...she strengthened a bit more than expected before landfall as detailed in special update #145A...but she has since weakened and is back on track with the previous intensity forecast. What is causing her weakening is that she is whirling beneath the less-divergent region of the paragraph P1 upper vortex. I continue to generally agree with the NHC's weakening rate since I am inexperienced with precisely predicting the max wind speed of a decaying non-tropical gale. However by Wednesday and Thursday..I still prefer to stay above the NHC intensity guidance as she may maintain strength or even re-strengthen a little if Sandy interacts with the eastern divergence of paragraph P1 shortwave upper trough soon to move across the Great Lakes.


Figure 1: Non-tropical gale Sandy Forecast

Impact swath in Figure 1 is a marriage of 11 PM EDT NHC tropical storm wind radius to the western boundaries of my previous impact swath...which still match up very well with the western extent of advisories...watches..and warnings still in effect from the United States National Weather Service local offices. A broad explanation of expected impacts within the swath is written in statements (a) through (e) in Figure 1. The following is a region-by-region breakdown of expected impacts...and additional details on your local watches and warnings can be found on www.nws.noaa.gov...

For the states of New Jersey...New York...Vermont...New Hampshire...Massachusetts...Connecticut...Rhode Island...Maryland...Delaware...Virginia...Pennsylv ania...and Washington DC...expect severe winds and potentially flooding rains to persist for the rest of the day and tonight. In a sizeable area around the storm center...while sustained wind will be in the tropical storm force range (40 to 70 mph)...an isolated gust to hurricane force (75+ mph) cannot be ruled out. Power outages continue to occur in a massive area in this region. Because of this...utilities in the region will need more time than usual to fix all affected areas...so power outages will last a long period. It will get cold in the wake of Sandy as she wraps in cold air on her back side...so have methods to stay warm without electricity for the next few days. Coastal storm surge in this region will gradually diminish today...but for your safety do not venture back until local officials permit you.

For southern Maine within the blue-dashed impact swath...rainfall with gusty and potentially damaging winds will diminish by tonight.

For the eastern Great Lakes inside the impact swath...the upper peninsula of Michigan inside of the impact swath...all of the lower peninsula of Michigan...the shores of Chicago, Illinois...and for the east half of Indiana...and the east half of Kentucky...the pressure gradient between the west side of Sandy and the strong central US surface ridge in paragraph P1 will tighten as Sandy pushes westward today. Due to the smooth surface of the lakewater...the northerly winds driven by the pressure gradient will not be limited by friction...and therefore are expected to be severe over the lakes and in areas just downwind of the lakes. Lake waters will therefore by choppy...and a storm surge can be expected on the north facing shores of the lakes. In lieu of this storm surge potential...coastal flood warnings...including for the shores of Chicago...have been issued where appropriate. Land areas within the blue-dashed impact swath and just downwind from the lakes in Michigan...northern Ohio...and NW Indiana can expect damaging winds with power outages. Even in areas quiet away from the lakes...wind gusts could reach tropical storm force (40+ mph) and cause scattered damage and power outages. Any power outages in this region are not expected to be as widespread as they are in the states to the east...so restoration of power will not take as long. As Sandy wraps in cold air on her back side...expect rain showers in this region to mix in with wet snow at times.

For the Appalachian mountains in western North Carolina...eastern Tennessee...northern Georgia...and all of West Virginia...expect major amounts of accumulating wet snow with severe and damaging winds in the higher elevations. This is because in the higher elevations...the wind will not be limited by surface friction...and the risk of downed trees and power outages is further increased by blowing wet snow accumulating on foliage. Where blowing snow will create visibility issues...blizzard warnings are in effect. Expect these conditions to be at their worst today when the pressure gradient between the west side of Sandy and the strong central US surface ridge in paragraph P1 will tighten as Sandy pushes westward.

For the southeastern United States...including Florida...Alabama...Georgia...South Carolina...and the piedmont and coastal plain of North Carolina...breezy conditions on the edge of Sandy's circulation may prompt lake wind advisories for small local lakes. This is because the wind over the lakes will not be as limited by land friction. In addition...because Sandy's cool air advection has amplified the paragraph P1 upper trough into a SW-NE tilted feature/upper vortex...western convergence of the tilting upper trough will support an impressive area of dry..sinking air to the south and southwest of Sandy. In fact this impressive dry air mass is already present in the above thermo birdseye chart. In areas covered by this dry air...the combination of breezy conditions and dry grassy land continues to trigger red flag warnings for fire risk.

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system across eastern North America is now entangled with non-tropical gale Sandy. See special update #145A for how Sandy's circulation transformed a fragment of the associated upper trough into an upper vortex located SW of Sandy. Remainder of this upper trough is located across the central US and will slowly push eastward toward Sandy via passing over the Great Lakes. Vast convergence west of this upper trough supports a strong 1028 mb ridge over the central US. The latent heat release of Sandy's large cloud field...coupled with immense low-level warm air advection ahead of Sandy's large circulation...is supporting a large north Atlantic upper anticyclone...which is a merger of the NW and NE Atlantic upper anticyclones mentioned in paragraphs P1 and P2 of discussion #145. The 1035 mb ridge SW of Greenland in paragraph P2 of previous discussion #145 has intensified to a maximum of 1038 mb on the east coast of Canada while supported by mass convergence between the westerlies ahead of the central US upper trough and easterlies streaming from the north Atlantic upper anticyclone.

P2...Deep-layered low pressure system/upper vortex persists in the central Atlantic. At the surface...their continues to be a broad low pressure spin in the low 990s of mb that has whirled into a position beneath the upper vortex. Meanwhile....the non-tropical remnant of Tony has been absorbed by the warm front extending east of the low-990s mb center. The low-990s broad surface low remains stalled between the surface ridging to the south in paragraph P5 and an intensifying 1038 mb ridge to the north mentioned in paragraph P1.

P3...Upper trough in the NE Atlantic appears to have retrograded westward and amplified in relatively lower pressures east of the the north Atlantic upper anticyclone in paragraph P1. The retrogression appears to have occurred thanks to retrograding of the north Atlantic upper anticyclone itself. It appears the north Atlantic upper anticyclone retrograded due to becoming associated with maximal warm air advection of Sandy's low-level circulation...which also is hooking westward.

...TROPICAL BELT DISCUSSION...
P4...Sprawling east-west tropical Atlantic upper anticyclone remains centered just NE of the Lesser Antilles. 24 hrs ago...an upper trough developed in relatively lower pressures east of the anticyclone...and now this upper trough is an upper vortex retrograding SW around the anticyclone. Upper divergence on the NW quad of the upper anticyclone supports a surface trough extending from south of Sandy into the NW Caribbean...as well as a surface trough SE of the Dominican Republic in the eastern Caribbean.

P5...Surface troughing midway between the Cape Verde Islands and the Lesser Antilles in paragraph P5 of the previous discussion persists while sandwiched between a 1013 mb ridge to the west and another 1016 mb ridge to the east. Both ridges appear to be supported by upper convergence on the SE quad of the east-west upper anticyclone mentioned in paragraph P4 above. Interestingly...the aforementioned surface troughing has gained some t-storm activity this evening despite being on what should be the upper convergent SE quad of this upper anticyclone. Will be watching to see if this surface trough/t-storm cluster moves directly under the axis of the upper anticyclone...in which case it would get enhanced upper outflow in all directions and potentially develop into another Atlantic tropical system.

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2012 Atlantic Hurricane Season Birdseye Discussion #145A (Special Update)

By: NCHurricane2009, 2:46 AM GMT on October 30, 2012

...MONDAY OCTOBER 29 2012...10:45 PM EDT...
Sandy makes history as a major and potentially devastating storm to the state of New Jersey and the New York City metro area.

Sandy intensified more than expected to 90 mph maximum sustained winds and 940 mb central pressure just prior to landfall in southern New Jersey. Cool air advection on the west side of the storm amplified the incoming upper trough (paragraph P1 feature of discussion #145) into an upper vortex to the southwest...and in turn this upper vortex whilred Sandy northwestward into landfall. Because Sandy intensified more than expected...the cool air advection was stronger than expected...causing the upper vortex to develop stronger and faster and whirl in Sandy faster...which explains Sandy's earlier than expected landfall. As for the unexpected amount of intensification...I believe Sandy tapped into extrodinary split flow upper divergence between the NE quad of the upper vortex and North Atlantic upper anticyclone (this North Atlantic upper anticyclone is a combo of the NW and NE Atlantic upper anticyclones mentioned in paragraphs P1 and P2 of discussion #145). Sandy may have had an upper anticyclonic outflow channel around this upper anticyclone potentially enhanced by her t-storm latent heat release. Furthermore...the split flow upper divergence between the upper anticyclone and upper vortex may have been further enhanced by westerly upper winds flowing into a central Atlantic deep-layered low (paragraph P2 feature of discussion #145). Just prior to landfall across southern New Jersey...Sandy weakened to 80 mph max winds with her central pressure rising into the 950 mb range. Expect Sandy to continue weakening as her center whirls into a non-divergent region of the aforementioned upper vortex.

In addition to wind damage and widespread power outages...New York City has broken its record for coastal storm surge..thanks to Sandy's unprecedently large wind field that pushed tons of water against the coast. The strong winds across New York City were northeasterly several hours before landfall...pushing water from the East River southwestward into the east shores of Manhattan and flooding East Village in Manhattan. Just after landfall...the strong winds across New York City switched to southeasterly...pushing the Atlantic Ocean northwestward into and against northerly flow of the Hudson and East Rivers...creating a record-breaking storm surge against the south-facing shores of Battery Park of Manhattan. This storm surge was made worse by its almost perfect phasing with high tide. Reports have come in suggesting this storm surge is flooding parts of New York City's subway system...the World Trade Center re-construction site...the runway of Laguardia Airport...the area around the New York Stock Exchange of Wall Street...and other areas of lower (southern) Manhattan. As of this writing...it appears the worst of the storm surge is over...as the southeasterly winds driving in the Atlantic Ocean are weakening over the area as the center of Sandy pushes further inland and away from this area.

Devastating and record-breaking storm surge apperas to have also slammed the east coast of New Jersey...but the effects to major areas such as Altantic City are not fully known at this time...

My next full blog update will be released sometime in the early morning just after midnight. However...their is a slight chance of power outage from where I am blogging...as wind gusts in my area in southeast Michigan have actually increased to 40+ mph in the last hour. Amazingly...this is occurring far away from the center of Sandy. In the slight chance that a power outage hits...my blog update will be delayed. Meanwhile...return to full discussion #145 for an update on the rest of the Atlantic tropics.

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2012 Atlantic Hurricane Season Birdseye Discussion #145

By: NCHurricane2009, 3:00 AM GMT on October 29, 2012

...SUNDAY OCTOBER 28 2012...11:10 PM EDT...
Fairly certain that Hurricane Sandy will become one of the most damaging storms in United States History as it transitions into an intense and large-sized non-tropical gale. Several watches and warnings across the mid-Atlantic and northeastern United States...as well as the Appalachian Mountains...eastern Ohio Valley...and the eastern Great Lakes region have been issued by the United States National Weather Service (www.nws.noaa.gov). Therefore a region-by-region breakdown of impacts is listed in the Sandy special feature section below. For additional details...visit www.nhc.noaa.gov...www.nws.noaa.gov...and listen to national media...local media...and local officials.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1337Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE SANDY...
Track-wise for Sandy...she continues moving NE in response to steering from the incoming paragraph P1 upper trough. Comparing today's tracking to my and the NHC's previous forecast track...Sandy has been positioned a little more south and east than expected. The more eastward (offshore) aspect of her track means she will more gradually advect in cold air beneath the paragraph P1 upper trough...which means the upper trough will more gradually amplify into an upper vortex that whirls her NW. This means the radius of the NW curving track will be a bit larger than previously thought. So even though she is more south than expected...I will not adjust my landfall point further south because the radius of the NW curving track will also be a bit larger as described above...so I still forecast a landfall in southern New Jersey around 11 PM Monday. The NHC in the last 24 hrs adjusted their forecast track to this landfall point...and today's 12Z GFS 36-hour forecast also agrees with this landfall point.

Because the 12Z GFS agrees with my landfall point and timing...I continue to rely on the 12Z GFS solution for what happens to Sandy after landfall. By landfall time...the 12Z GFS shows the paragraph P1 upper trough split into an upper vortex to the south that should whirl her westward into south-central Pennsylvania...and shortwave upper trough moving towards the Great Lakes. It then has the upper vortex shoot NE and dissipate...which would mean Sandy would cyclonically loop on the NW side of the dissipating upper vortex as I show for Tuesday. By Wednesday and Thursday...Sandy would then be in a position to be lifted northward by the shortwave upper trough moving across the Great Lakes...but interestingly the 12Z GFS shows Sandy's cool air advection amplify this shortwave into a new upper vortex in the vicinity and to the south. Afterwards...this upper vortex shoots NE...and so I have Sandy make another small cyclonic loop on Thursday around the west side of NE-shooting upper vortex. This NE shooting upper vortex's eastern divergence also creates a new surface low by Friday located NE of Sandy...and I expect this new surface low's south side to pull Sandy ENE and absorb her.

Intensity-wise for Sandy...normally I do not predict intensity forecast points for the non-tropical phase of a tropical cyclone...but this event is going to be so significant for the mid-Atlantic and NE US that I feel I must. The NHC and I agree continue to agree that Sandy will have potential to strengthen a bit as she makes landfall...but this is through non-tropical processes as Sandy takes maximum advantage of upper divergence on the east side of the paragraph P1 upper trough. I continue to expect transition to non-tropical by 11 AM Monday. She will then whirl beneath the less-divergent axis of the amplifying paragraph P1 upper trough...causing her to weaken as a post-mature non-tropical gale as she moves inland...and I continue to generally agree with the NHC's weakening rate since I am inexperienced with precisely predicting the max wind speed of a decaying non-tropical gale. However by Thursday..I still prefer to stay above the NHC intensity guidance as she may maintain strength or even re-strengthen a little if Sandy interacts with the eastern divergence of a shortwave upper trough moving across the Great Lakes as the 12Z GFS shows.


Figure 1: Hurricane Sandy Forecast

The eastern half of my impact swath is based on my projected track and taking Sandy's 5 PM EDT tropical storm (40+ mph) wind radius and expanding it in the NE half of the storm as she intensifies non-tropically...then shrinking the NE half of the wind radius as Sandy subsequently weakens non-tropically. The reason I only expand the NE half of the radius during non-tropical intensification is because her SW half should whirl in dry and cold air beneath the upper trough axis...while her NE half stays very moist. It is the rain bands in the NE half that will then mix down the strong upper-level winds of the paragraph P1 upper trough's jet stream to the surface. It should be noted that the 5 PM EDT radius that I used today is larger than yesterday's...as Sandy once again has undergone more growth due to eastern divergence of the incoming paragraph P1 upper trough. Today's growth has been mostly in the NE half...so in particular my impact swath has undergone a significant northward expansion compared to my previous. My impact swath has also undergone quiet an expansion to the west compared to my previous...due to several advisories...watches...and warnings that have been raised over the eastern Great Lakes area...Ohio Valley area...and the Appalachian Mountains.

A broad explanation of expected impacts within the swath is written in statements (a) through (e) in Figure 1. The following is a region-by-region breakdown of expected impacts...and additional details on your local watches and warnings can be found on www.nws.noaa.gov...

For the states of New Jersey...New York...Vermont...New Hampshire...Massachusetts...Connecticut...Rhode Island...Maryland...Delaware...Virginia...Pennsylv ania...and Washington DC...expect a prolonged period of severe winds and potentially flooding rains late Monday and all of Tuesday. Near the landfall site of the storm center...sustained winds and higher gusts will reach hurricane force (75+ mph). In a sizeable area around the storm center...while sustained wind will be in the tropical storm force range (40 to 70 mph)...gusts could also hit hurricane force (75+ mph). Power outages will affect millions in a large area. Because of this...utilities in the region will need more time than usual to fix all affected areas...so power outages will last a long period. It will get cold in the wake of Sandy as she wraps in cold air on her back side...so have methods to stay warm without electricity for the next few days. On coastal areas susceptible to storm surge...the storm surge will be historic even though Sandy is only a category 1 hurricane. This is because Sandy has one of the largest wind radii ever seen in such a hurricane...and the large radius of winds will push severe amounts of water against the coast. Therefore...failure to obey mandatory evacuation orders in storm surge prone areas will result in certain risk to your life. In recent news...the mayor of New York City has ordered evacuations in low-lying coastal areas...as the subway system has been shut down to make preparations to seal the entry ways from storm surge flooding.

For the state of Maine...especially southern Maine...rainfall with gusty and potentially damaging winds are on the way for the latter portion of Monday. While the wind and flooding impacts are not likely to be as severe as in the New England states to the south...these impacts should be taken with respect.

For NE North Carolina...and the northern Piedmont of North Carolina...my impact swath in Figure 1 shows more of the NE portion of the state covered than previous...due to persistent rain bands on the west side of Sandy that have been affecting the area. Although this small piece of the swath is outside the 5 PM EDT NHC tropical storm wind radius...this piece of the swath is to emphasize the potential for flooding due to the long-lasting nature of these rain bands. More of the north half of North Carolina is covered by the impact swath in Figure 1 than my previous impact swath. This is because Sandy's southern tropical storm wind radius has continued to grow thru 5 PM EDT today...and I simply extrapolated that southern tropical storm wind radius along my forecast track with the assumption that the expected strengthening on Monday and subsequent weakening on Tuesday means that Sandy maintains this southern radius for quiet a period. This now means the northern Piedmont of North Carolina can expect wind gusts reaching tropical storm force (40+ mph) on Tuesday...resulting in some light damage and power outages. Because the power outages won't be as widespread as they will be to the north...any power loss should be restored in a quicker timeframe.

For the eastern Great Lakes inside the impact swath...the upper peninsula of Michigan inside of the impact swath...all of the lower peninsula of Michigan...the shores of Chicago, Illinois...and for the east half of Indiana...and the east half of Kentucky...the pressure gradient between the west side of Sandy and the strong central North America surface ridge in paragraph P1 will tighten as Sandy pushes westward on Tuesday. Due to the smooth surface of the lakewater...the northerly winds driven by the pressure gradient will not be limited by friction...and therefore are expected to be severe over the lakes and in areas just downwind of the lakes. Lake waters will therefore by choppy...and a storm surge can be expected on the north facing shores of the lakes. In lieu of this storm surge potential...coastal flood warnings...including for the shores of Chicago...have been issued where appropriate. Land areas within the blue-dashed impact swath and just downwind from the lakes in Michigan...northern Ohio...and NW Indiana can expect damaging winds with power outages. Even in areas quiet away from the lakes...wind gusts could reach tropical storm force (40+ mph) and cause scattered damage and power outages. Any power outages in this region are not expected to be as widespread as they are in the states to the east...so restoration of power will not take as long. As Sandy wraps in cold air on her back side...expect rain showers in this region to mix in with wet snow at times.

For the Appalachian mountains in western North Carolina...eastern Tennessee...northern Georgia...and all of West Virginia...expect accumulating wet snow with severe and damaging winds in the higher elevations. This is because in the higher elevations...the wind will not be limited by surface friction...and the risk of downed trees and power outages is further increased by blowing wet snow accumulating on foliage. Where blowing snow will create visibility issues...blizzard warnings are in effect. Expect these conditions to be at their worst on Tuesday when the pressure gradient between the west side of Sandy and the strong central North America surface ridge in paragraph P1 will tighten as Sandy pushes westward.

For the southeastern United States...including Florida...Alabama...Georgia...South Carolina...and the southern piedmont of North Carolina...breezy conditions on the edge of Sandy's circulation may prompt lake wind advisories for small local lakes. This is because the wind over the lakes will not be as limited by land friction. In addition...as Sandy's cool air advection amplfies the paragraph P1 upper trough into a SW-NE tilted feature and then into an upper vortex...western convergence of the tilting upper trough will support an impressive area of dry..sinking air to the south and southwest of Sandy. In fact this impressive dry air mass is already present in the above thermo birdseye chart. In areas covered by this dry air...the combination of breezy conditions and dry grassy land has triggered red flag warnings for fire risk.

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system across central North America is working its way into eastern North America and toward Hurricane Sandy. In the upper-levels...the system continues to be anchored by a large upper trough currently over the central US. Vast convergence west of this upper trough supports a strong 1030 mb ridge over central North America. Vast divergence east of this upper trough formerly supported a 974 mb gale over northern Hudson Bay 24 hrs ago...which has since been deflected northward out of the picture and weakened while steered around the west side of the intensifying 1035 mb ridge in paragraph P2. The front attached to that gale however has continued eastward and is about to merge with Hurricane Sandy...which will give Sandy air mass contrasts as she becomes non-tropical in the next 24 hrs. The latent heat release of Sandy's large cloud field...coupled with low-level warm air advection ahead of Sandy's large circulation...is supporting a large NW Atlantic upper anticyclone and will soon be supporting the large NE Atlantic upper anticyclone mentioned in paragraph P2. It is not out of the question that both upper anticyclones merge into one large north Atlantic upper anticyclone supported by intense low-level warm air advection ahead of what is expected to be an impressive non-tropical version of Sandy.

P2...Deep-layered low pressure system/upper vortex persists in the central Atlantic. At the surface...their continues to be a broad low pressure spin in the low 990s of mb that has whirled into a position beneath the upper vortex. Meanwhile....the non-tropical remnant of Tony has stalled midway between the Azores and Canary Islands...and the region of eastern upper air divergence of the upper vortex has caught up to Tony such that Tony has stopped weakening. Both Tony and the aforementioned low-990s broad surface low have become stalled between the 1015 mb ridging to the south in paragraph P5 and an intensifying 1035 mb ridge to the north centered just SW of Greenland. This 1035 mb ridge is from the remnants of east North America surface ridge formerly supported by the western convergence of the upper vortex...but now supported by convergence between westerlies streaming from the paragraph P1 upper trough and easterlies streaming from the NE Atlantic upper anticyclone mentioned in paragraph P2 of the previous discussion. This NE Atlantic upper anticyclone used to be supported by warm air advection ahead of the aforementioned low-990s broad surface low...but will soon by supported by warm air advection ahead of Sandy.

P3...Upper trough in the NE Atlantic has moved ever so slowly eastward into western Europe while cut-off from the mid-latitude jet stream at a location SE of the NE Atlantic upper anticyclone mentioned in paragraphs P1 and P2. Trailing cold front from surface frontal low supported by eastern divergence of this upper trough continues to be marked in the upper-right corner of the above atmo chart.

...TROPICAL BELT DISCUSSION...
P4...Upper ridge in the eastern tropical Atlantic...mentioned in paragraph P4 of the previous discussion...has become replaced by sprawling east-west tropical Atlantic upper anticyclone centered just NE of the Lesser Antilles. This sprawling upper anticyclone was formerly the warm core upper anticyclone/outflow structure of Hurricane Sandy when she was in the Caribbean days ago...but was sheared-off the hurricane by a west Cuba upper vortex mentioned in the Sandy special feature sections written over the previous days. What is left of the west Cuba upper vortex is now an upper trough over Florida and central Cuba. In relatively higher pressures SW of that upper trough and south of the paragraph P1 upper trough...an upper ridge is building over Central America.

P5...Pair of tropical waves midway between the Cape Verde Islands and the Lesser Antilles in paragraph P4 of the previous discussion has decayed into a pair of surface troughs sandwiched between a 1015 mb ridge to the west and another 1015 mb ridge to the east. The western 1015 mb ridge is supported by upper convergence on the SE quad of the east-west upper anticyclone mentioned in paragraph P4 above. The eastern 1015 mb ridge is a weaker version of the 1018 mb east Atlantic ridge mentioned in paragraph P3 of the previous discussion. This eastern ridge is now weakening in a vast region of split flow upper divergence between the paragraph P4 east-west upper anticyclone and paragraph P2 upper vortex.

Updated: 3:15 AM GMT on October 29, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #144B (Special Update)

By: NCHurricane2009, 12:17 AM GMT on October 29, 2012

...SUNDAY OCTOBER 28 2012...8:16 PM EDT...
Fairly certain that Hurricane Sandy will become one of the most damaging storms in United States History as it transitions into an intense and large-sized non-tropical gale. Several watches and warnings across the mid-Atlantic and northeastern United States...as well as the Appalachian Mountains...eastern Ohio Valley...and the eastern Great Lakes region have been issued by the United States National Weather Service (www.nws.noaa.gov).

In special update #144A earlier this afternoon...I had promised a full blog update showing a region-by-region breakdown of Sandy's expected impacts by 7 to 8 PM EDT. It is taking more time than previously anticipated to finish this blog update. Therefore...it could be as late as midnight EDT before I get this update out.

Return to full discussion #144 for an assessment on the rest of the Atlantic tropics...

Updated: 2:50 AM GMT on October 29, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #144A (Special Update)

By: NCHurricane2009, 8:29 PM GMT on October 28, 2012

...SUNDAY OCTOBER 28 2012...4:30 PM EDT...
Fairly certain that Hurricane Sandy will become one of the most damaging storms in United States History as it transitions into an intense and large-sized non-tropical gale. Several watches and warnings across the mid-Atlantic and northeastern United States...as well as the Appalachian Mountains...eastern Ohio Valley...and the eastern Great Lakes region have been issued by the United States National Weather Service (www.nws.noaa.gov). Therefore a region-by-region breakdown of impacts will follow on my next full blog update...which should be released around 7 to 8 PM EDT...

Return to full discussion #144 for an assessment on the rest of the Atlantic tropics...

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2012 Atlantic Hurricane Season Birdseye Discussion #144

By: NCHurricane2009, 8:21 PM GMT on October 27, 2012

...SATURDAY OCTOBER 27 2012...4:20 PM EDT...
This is one of the most important birdseye discussions due to the ominous threat that Sandy brings to the mid-Atlantic and northeastern United States. Preparations in these areas should be pushed to completion this weekend as landfall is imminent on Monday. For coastal areas along the mid-Atlantic and northeastern United States...pay attention to local officials for mandatory evactuation orders associated with storm surge threat. For areas coastal and inland on the mid-Atlantic and northeastern United States...a large area of damaging 40+ mph sustained winds appears imminent...see blue-dashed impact swath in Figure 1 of the Sandy special feature section for current best guess of where these winds are likely to be. Be prepared for power outages that last for days in this region...and keep in mind methods to stay warm without power as it will get cold as Sandy wraps in cold air on her back side. For additional details...see the Sandy special feature section below...and visit www.nhc.noaa.gov...www.nws.noaa.gov...and listen to national media...local media...and local officials.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1328Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE SANDY...
Concerning the east coast of the United States...offshore western Atlantic waters...and interior sections of the mid-Atlantic and parts of the northeastern United States located inside the blue-dashed impact swath of Figure 1...impact statments (a) through (c) are fairly descriptive of what is likely ahead. Please take these hazards seriously and listen to local officials and media. Latest coastal watches and warnings are found under the public advisory for Sandy at www.nhc.noaa.gov. Latest local forecast statements...for the coast and inland areas...for those likely to be affected by Sandy are found at www.nws.noaa.gov.

Track-wise for Sandy...kudos to the GFS model which during the previous discussion predicted a brief period of an eastward track for today that has actually occurred in response to blocking effect of 1032 mb North America surface ridge (paragraph P1) and attaraction toward paragraph P2 deep-layered low pressure system. As of 2 PM EDT...Sandy has begun accelerating NE in response to steering from the incoming paragraph P1 upper trough. While the NHC track forecast in Figure 1 and the 12Z GFS model for today are in strong agreement for the short-term...and while the current direction of travel aligns with both of these solutions...the recent NE acceleration is occuring faster than shown by both of those solutions. Therefore my track forecast in Figure 1 agrees with the direction of travel shown by NHC...but I disagree with the forward speed and instead show a faster forward speed. My current track forecast in Figure 1 now has the center moving into New Jersey...while the NHC forecast track has the center moving into Delaware. The reason for my northward bias is that by the time Sandy hooks to the west...she should be further north due to her current faster-than-expected NE acceleration which I extrapolated.

What causes her westward hook into the US is her interaction with the incoming paragraph P1 upper trough. She will take maximum advantage of the eastern divergence of the incoming paragraph P1 upper trough and intensify non-tropically. Cool air advection on her back side in turn will amplify the upper trough into an upper vortex that would whirl her NW and eventually W.

Even though the 12Z GFS initially agrees with the too-sluggish NE track shown by NHC in Figure 1...the 12Z GFS between 48 and 60 hrs suddenly catches up to my landfall point shown in Figure 1...and so for now I rely on the 12Z GFS solution for what happens to Sandy after landfall. By landfall time...the 12Z GFS shows the paragraph P1 upper trough split into an upper vortex over North Carolina and shortwave upper trough moving towards the Great Lakes. It has the North Carolina upper vortex shoot NE and dissipate...which would mean Sandy would cyclonically loop on the NW side of the dissipating upper vortex as I show for Tuesday. By Wednesday and Thursday...Sandy would then be in a position to be lifted northward by the shotwave upper trough moving across the Great Lakes...but interestingly the 12Z GFS shows Sandy's cool air advection amplify this shortwave into a new upper vortex over western NY state by Thursday. Afterwards...this upper vortex shoots NE...and so I have Sandy make another small cyclonic loop on Thursday around the west side of NE-shooting upper vortex.

Intensity-wise for Sandy...normally I do not predict intensity forecast points for the non-tropical phase of a tropical cyclone...but this event is going to be so significant for the mid-Atlantic and NE US that I feel I must. After weakening into a strong tropical storm (70 mph max winds) early this morning...she regained hurricane status (75+ mph max winds) after her tremendous cloud field's latent heat release punched out what has been an upper vortex near west Cuba that delivered dry air and southerly shear into the system. Due to her dramatically improved satellite appearance...my intensity forecast in Figure 1 for the next 12 hours suggests possible additional strengthening using tropical methods (t-storm latent heat release enhancing her anticyclonic upper outflow). Alternatively...the NHC prefers to maintain her current strength for the next 12 hours. After 12 hours...I re-join the NHC intensity forecast of 75 mph max winds as southwest vertical shear should increase from the paragraph P1 upper trough. The NHC and I agree that Sandy will have potential to strengthen a bit as she makes landfall...but this is through non-tropical processes as Sandy takes maximum advantage of upper divergence on the east side of the upper trough. I delayed transition to non-tropical by 12 hours from my previous...due to her currently-impressive and more tropical satellite appearance. She will then whirl beneath the less-divergent axis of the amplifying paragraph P1 upper trough...causing her to weaken as a post-mature non-tropical gale as she moves inland...and I use the NHC's weakening rate since I am inexperienced with precisely predicting the max wind speed of a decaying non-tropical gale. However by Thursday..I prefer to stay above the NHC intensity guidance as she may maintain strength or even re-strengthen a little if Sandy interacts with the eastern divergence of a shortwave upper trough moving across the Great Lakes as the 12Z GFS shows.


Figure 1: Hurricane Sandy Forecast

My impact swath initialization in Figure 1 is based on extrapolating the 11 AM tropical storm wind radius along my forecast track. This wind radius is larger than yesterday's...because Sandy's low pressure field size got another boost while taking advantage of mass split flow upper divergence between the dissipating upper vortex over west Cuba and her own warm core upper anticyclone. Therefore...my impact swath includes more areas than it did previously...and is also adjusted northward due to my northward adjustment in forecast track from my previous. Notice that late in the forecast...I expand the wind (impact swath) radius only in the NE half of the storm as she intensifies non-tropically. This is because as Sandy becomes non-tropical...her SW half will whirl in dry and cold air beneath the upper trough axis...while her NE half stays very moist. It is the rain bands in the NE half that will then mix down the strong upper-level winds of the paragraph P1 upper trough's jet stream to the surface. The storm surge threat is emphasized in impact statement (a)...because even though Sandy is only a category 1 hurricane by max winds...her wind field diameter is one of the largest ever for such a hurricane such that she will push far more water than a usual category 1 hurricane does.

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system across central North America is working its way into eastern North America in the last 36 hrs. In the upper-levels...the system continues to be anchored by a large upper trough which has moved from the western to the central US. Vast divergence east of this upper trough has developed an intense 974 mb frontal gale over Hudson Bay in northern Canada....while vast convergence west of this upper trough supports a strong 1032 mb ridge centered over the central US. Low-level warm air advection ahead of the gale supports an upper ridge axis which has mostly joined Sandy's gigantic warm core upper anticyclonic outflow in the last 36 hrs.

P2...Deep-layered low pressure system/upper trough is moving from the western to central Atlantic. At the surface...their continues to be a broad low pressure spin in the low 990s of mb supported by eastern divergence of the upper trough. Meanwhile....the non-tropical remnant of Tony has conitnued ENE into the NE Atlantic...currently located midway between the Azores and Canary Islands at a location where it has escaped the aformentioned eastern upper divergence such that it has been weakening. Cool air advection of the aforementioned broad surface low continues to keep the upper trough amplified into an upper vortex. Meanwhile...eastern North America surface ridge supported by western upper convergence of this upper trough has become increasingly eroded in advance of 974 mb frontal gale mentioned in paragraph P1. Lastly...warm air advection ahead of the aforementioned broad surface low is maintaining the full-fledged NE Atlantic upper anticyclone.

P3...Upper trough in the NE Atlantic is moving ever so slowly eastward into western Europe while cut-off from the mid-latitude jet stream at a location SE of the upper anticyclone mentioned in paragraph P2 above. Upper convergence on the west side of the upper trough supports 1015 mb surface ridge in the eastern Atlantic. 1000 mb low associated with this system in the previous discussion has moved into western Europe over the last 36 hrs...and trailing from it is a cold front marked in the upper-right corner of the above atmo chart.

...TROPICAL BELT DISCUSSION...
P4...Upper ridge in the eastern tropical Atlantic persists. Pair of tropical waves WSW of the Cape Verde Islands in the previous discussion is now midway between the Cape Verdes and Lesser Antilles. Shower and t-storm activity with these features have declined in the last 36 hrs while leaving the favorable upper outflow of the east tropical Atlantic upper ridge...and while entering an area of dry air from the upper convergent SE quad of the massive upper anticyclonic flow associated with Hurricane Sandy.

Updated: 5:10 PM GMT on October 28, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #143

By: NCHurricane2009, 12:29 PM GMT on October 26, 2012

...FRIDAY OCTOBER 26 2012...8:30 AM EDT...
As weather conditions gradually improve in the Bahamas...Hurricane Sandy making a westward jab in track closer to the United States east coast...and as a result it is now clear that Sandy will be bringing its wrath toward the mid-Atlantic and parts of the northeast United States as an intensifying non-tropical gale by early next work week. See the Sandy special feature section below for additional details on this potentially historic storm.

Tony continues east-northeast across the open Atlantic...and has completed transition into a non-tropical surface low during the last 24 hrs. See paragraph P2 for statement on remnant of Tony.

Tropical wave activity west-southwest of the Cape Verde Islands...associated with a pair of tropical waves in paragraph P4 of the tropical belt discussion...continues struggling under less favorable upper winds.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1933Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE SANDY...
Concerning the east coast of the United States...offshore western Atlantic waters...and interior sections of the mid-Atlantic and parts of the northeastern United States located inside the blue-dashed impact swath of Figure 1...impact statments (a) through (c) are fairly descriptive of what is likely ahead. Please take these hazards seriously and listen to local officials and media. Latest coastal watches and warnings are found under the public advisory for Sandy at www.nhc.noaa.gov. Latest local forecast statements...for the coast and inland areas...for those likely to be affected by Sandy are found at www.nws.noaa.gov.

Track-wise for Sandy...she has hooked more leftward than I previously anticipated. In fact...I previously had not anticipated the leftward hook at all. It appears over the last couple of days...a vast region of split flow upper divergence between Sandy's warm core upper anticyclone and an upper vortex near west Cuba significantly expanded the size of the hurricane's cloud field...particularly north and east of the center. In turn...the latent heat release of this gigantic cloud field has recently amplified the warm core upper anticyclone against the upper vortex...causing the definition of the upper vortex to be more amplified. Sandy's leftward (westward) hook is the result of her getting steered by the NE quad of the amplified upper vortex in conjunction with the south side of the E North America surface ridge mentioned in paragraph P2. When comparing the 00Z GFS initialization with the above atmo chart...it is clear the GFS has underplayed the amplitude of the upper vortex and placed it too far west...so in response I have my forecast track left of the 00Z GFS and left of the NHC track. After 11 PM tonight...Sandy should still turn more NE and offshore because the models create a strong North America surface ridge on the convergent back side of the paragraph P1 upper trough...and such a ridge would block a continued NW track into the SE US. It is interesting to note the 00Z GFS by 11 PM Saturday has Sandy going straight east for a brief period...but I think it now overdoes the attraction to the paragraph P2 cyclone because I am now to the left of the GFS. Therefore...I do not expect a brief period of a straight eastward track.

It is clear the non-tropical version of Sandy will not continue NE out to sea. Instead...she will hooks leftward toward the NE and mid-Atlantic US. Her westward adjustment in track means that she will be hugged by a fragment of the North America surface ridge to the north...and that she will interact with the paragraph P1 upper trough. She will take maximum advantage of the eastern divergence of the incoming paragraph P1 upper trough and intensify non-tropically. Cool air advection on her back side in turn will amplify the upper trough into an upper vortex that would whirl her NW. The closer Sandy is to the US shore...the stronger the cool air advection...and the faster the amplification into an upper vortex such that the radius of the NW curving track is tighter. That is why my forecast track has a tighter radius than the more offshore GFS and NHC solutions.

Intensity-wise for Sandy...she has weakened from a category 2 to 1 hurricane in the last 24 hrs as the aforementioned mass area of split flow upper divergence has broadened her low pressure field. This broadening has made her pressure gradient more lax...and that is why her winds have died down. But despite the max winds dying down...her tropical storm wind radius has gone up due to the expansion of the low pressure field size. Her satellite apperance does not resemble a hurricane...so I expect her to soon be downgraded to a strong tropical storm of 70 mph max winds. She could even be downgraded to a subtropical storm due to her interaction with the upper vortex near the west tip of Cuba. I still insist on transition to non-tropical by 11 PM Sunday...then possible re-intensification of Sandy as a non-tropical gale of 75 mph (minimal hurricane) max winds for her mid-Atlantic/NE US landfall on Monday. That is why their is mention of coastal and inland wind damage toward the storm center in impact statement (c) of Figure 1. She will then whirl beneath the less-divergent axis of the amplifying paragraph P1 upper trough...causing her to weaken as a post-mature non-tropical gale as she moves inland. That is why impact statement (c) says she will weaken as she moves inland.


Figure 1: Hurricane Sandy Forecast

My impact swath initialization in Figure 1 is based on extrapolating the 5 AM tropical storm wind radius along my forecast track. Notice that late in the forecast...I expand the wind (impact swath) radius only in the NE half of the storm as she intensifies non-tropically. This is because as Sandy becomes non-tropical...her SW half will whirl in dry and cold air beneath the upper trough axis...while her NE half stays very moist. It is the rain bands in the NE half that will then mix down the strong upper-level winds of the paragraph P1 upper trough's jet stream to the surface.

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system in the mid-latitudes is now advancing eastward into central North America this morning. In the upper-levels...the system continues to be anchored by a large upper trough from the western US whose western convergence supports a 1027 mb ridge. Vast divergence east of this upper trough continues driving a few frontal depressions across the central US. Low-level warm air advection ahead of the frontal depressions supports an upper ridge that has moved from the central to the eastern US.

P2...Deep-layered low pressure system/upper trough centered over SE Canada has finally fully shifted into the western Atlantic. In the last 24 hrs...the original surface center of this of this system has phased out offshore of the Canadian east coast...while the newer less-than-1004 mb center offshore of Newfoundland in the previous discussion has intensified to less-than-992 mb while supported by the eastern divergence of the upper trough. This same eastern divergence in the last 24 hrs has transitioned Tropical Storm Tony into a non-tropical low as it tracks ENE. Cool air advection behind the intensifying less-than-992 mb surface low pressure has caused the upper trough to amplify into an upper vortex stacked above the surface low. Meanwhile...1026 to 1027 mb surface ridge over eastern North America remains supported by western upper convergence of the upper trough. Warm air advection ahead of the aforementioned less-than-992 mb cyclone is maintaining the full-fledged NE Atlantic upper anticyclone.

P3...Upper trough in the NE Atlantic remains stalled offshore of Spain and Portugal to the SE of the upper anticyclone mentioned in paragraph P2 above. Upper convergence on the west side of the upper trough supports 1018 mb surface ridge in the eastern Atlantic. 996 mb gale in the previous discussion has moved eastward and weakened to about 1000 mb while passing below the non-divergent upper trough axis...and its east side has absorbed the remnant low of Rafael.

...TROPICAL BELT DISCUSSION...
P4...Upper ridge in the eastern tropical Atlantic persists. Pair of tropical waves WSW of the Cape Verde Islands continue to produce enhanced showers and t-storms under the favorable upper outflow of the upper ridge...and the western of the two tropical waves has spun up a 1008 mb surface low that was briefly organized yesterday afternoon and early evening. However...this activity has since become less organized this early morning as the tropical waves continue to struggle in southerly vertical shear on the west side of the upper ridge.

Updated: 5:11 PM GMT on October 28, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #142

By: NCHurricane2009, 12:27 PM GMT on October 25, 2012

...THURSDAY OCTOBER 25 2012...8:27 AM EDT...
As predicted in special update #141A last afternoon...Sandy rapidly intensified into a strong category 2 hurricane just before landfall across eastern Cuba in the overnight hours...resulting in the strongest landfall of the 2012 Atlantic hurricane season so far. Looking ahead...portions of the Bahamas can expect significant to intense weather conditions throughout today and part of Friday. Long-range fate of Sandy remains uncertain...with a slight chance of a historic "perfect storm" scenario for the northeastern United States or Atlantic Canada as Sandy becomes non-tropical early next week. See the Sandy special feature section below for additional details on this escalated situation.

Tropical Storm Tony continues east-northeast across the open Atlantic...soon to transition into a non-tropical system. See the Tony special feature section for additional details.

Tropical wave activity west-southwest of the Cape Verde Islands...associated with a pair of tropical waves in paragraph P4 of the tropical belt discussion...has become less organized while sliding into less favorable upper winds.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0125Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE SANDY...
Where warnings are in effect...preparations for Sandy in the Bahamas should have been completed by now with the storm expected to affect the warned areas thru the rest of today and Friday. Under the guise of impact statement (b) in Figure 1...Haiti and the Dominican Republic can expect continued heavy rains with potential flash floods and mudslides...with all of Haiti getting some gusty winds for the remainder of today as the impact swath in Figure 1 shows.

Concerning the east coast of North America and Bermuda...tropical storm watches have been issued for the east coast of Florida...but the impact info in Figure 1 suggests that SE Florida should at most see increased sea swells and rip currents on the coast. However...residents of east Florida should be aware in case the storm hooks more leftward than expected in track. Their remains debate about the long-term solution of Sandy beyond the scope of the forecast track in Figure 1. Forecasts such as the one I present in Figure 1 are less threatening to the NE United States and Atlantic Canada...but moreso to Bermuda. The GFS...GFDL...and Euro models show a system hooking leftward as an intensifying non-tropical gale...with the GFDL and Euro showing a strike to the NE United States...and the 00Z GFS showing a strike to Atlantic Canada.

Latest watches and warnings are found under the public advisory for Sandy at www.nhc.noaa.gov.

Track-wise for Sandy...while steered around the upper vortex near west Cuba...she continues tracking a bit to the right of the NHC solution as seen in Figure 1 above...and therefore my short-term track forecast reflects this. I do not show the short-term hook back to the left the NHC and computer models show. This hook I believe is Sandy getting attracted to some surface pressure falls in split flow upper divergence between the upper vortex near west Cuba and her own upper anticyclone. I believe with her tendency to track to the right of the NHC and further away from the spit flow upper divergence region...I am expecting a low chance that such an interaction will take place. 11 PM Thu continues to be coincident with when the GFS model shows the paragraph P2 E North America surface ridge N of Sandy at peak strength...so I agree with the slower NHC forecast track between 11 PM Thu and 11 PM Fri...but I am a hair faster than the NHC during this timeframe because this is also when that ridge weakens. Beyond 11 PM Fri...I have adjusted my track northward to give more respect to the NHC forecast and computer model runs...but I still have a rightward and more offshore bias with respect to NHC's solution. I still agree with my more offshore solution because the GFS still creates a strong North America surface ridge on the convergent back side of the paragraph P1 upper troughing...and such a ridge would block progression toward North America. Instead...the system would get attracted toward the paragraph P2 deep-layered cyclone (which should be east of Sandy by the end of the 5-day forecast in Figure 1)...much like how during discussion #107 when Nadine got pulled ENE toward the ex-Isaac deep-layered cyclone. Because we had previously under-predicted Nadine's ENE acceleration in such a scenario...another reason I prefer to show my more offshore track in Figure 1.

Whether the non-tropical remnant of Sandy continues NE out to sea...or whether she hooks leftward toward the NE US or Atlantic Canada depends on how much the North America surface ridge hugs the storm to the north...and depends on how interaction she has with the paragraph P1 upper trough. Such an interaction requires that Sandy is close enough or aligns with the paragraph P1 upper trough such that she takes maximum advantage of the eastern divergence of the upper trough and intensifies non-tropically. Cool air advection on her back side in turn amplifies the upper trough into an upper vortex that would whirl her NW. The Euro model and GFDL model shows a "perfect storm" scenario with a non-tropical Sandy slamming into the NE US at an awesome central pressure between 920 to 940 mb...but such a perfect scenario requires such perfect alignment with the paragraph P1 upper trough. Statistics are usual against perfect storm scenarios...so I am not buying into this solution at this time. However...residents on the coasts of the NE US and Atlantic Canada should be aware of this scenario in case the situation does escalate to "perfect storm" status.

Intensity-wise for Sandy...since she lost her well-defined eye while crossing east Cuba in the overnight...I show no re-strengthening. Rather...I maintain the current strength...then weaken Sandy coincident with when the 00Z GFS shows SW vertical shear increasing ahead of the paragraph P1 upper trough. I continue to show transition to non-tropical by 11 PM Sunday...when she should be well-buried in the eastern divergence of the paragraph P1 upper trough when comparing my forecast position to the 00Z GFS model run.


Figure 1: Hurricane Sandy Forecast

My impact swath initialization in Figure 1 is larger in the east quadrants than my previous. This swath size continues to be based on Sandy's central-dense overcast...and also the adjacent spiral band to the east. It is the growth of the spiral band on satellite that forces me to expand my impact swath size to the east. This swath is still larger than the tropical storm wind radius shown in the 5 AM EDT NHC advisory...but nonetheless their can easily be heavy flooding rains within the swath even if the winds on the outer edge of the swath are not that strong. Satellite imagery shows that the eastern divergence of the cut-off upper vortex near west Cuba has expanded the moisture field hundreds of miles to the north and east of Sandy itself...which is why impact statement (b) in Figure 1 is written. Such far-reaching rain bands are less likely on the west side of Sandy due to the suppression by the cut-off upper trough near the Isle of Youth...followed by suppression from the incoming paragraph P1 upper trough. These suppressive effects are also why I maintain an east bias with my impact swath when compared to my forecast track.

...SPECIAL FEATURE...TROPICAL STORM TONY...
Tony is interacting with the eastern divergence of the upper trough in paragraph P2...and his rapid ENE track has taken him across the 26 deg C isotherm into increasingly cooler waters. Therefore...he will continue a gradual transition into a non-tropical feature...which I continue to forecast will occurr by late this morning as I showed previously. Tony has tracked faster than thought...and will be near 35W longitude by later this morning as opposed to 40W longitude as previously thought. Because his fast ENE track shows a slight rightward angle compared to the NHC 5 AM forecast...my forecast track in Figure 2 is a little south of that forecast.


Figure 2: Forecast for Tropical Storm Tony

Impact swath in Figure 2 is based on the size of the tropical storm wind radius shown in the NHC 5 AM advisory package...and extrapolating that along the forecast track.

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system in the mid-latitudes continues entering from SW Canada and the western US in the upper-left corner of the above atmo chart. In the upper-levels...the system previously has two impulses...with the first upper trough moving from the Great Lakes/Ohio Valley and into the paragraph P2 upper trough where it is no longer distinct. Vast divergence east of the second upper trough continues driving a few frontal depressions across the western and central US. Low-level warm air advection ahead of the frontal depressions supports an upper ridge persisting over the central US. Upper westerlies across the upper ridge are in directional shear with low-level southerlies ahead of the frontal depressions. Therefore with enough instability from daytime heating of land later today...their is a risk of severe t-storms and tornadoes across portions of the north-central US and Great Lakes region. Visit www.nws.noaa.gov for up to the minute info on severe weather potential...including any active watches or warnings.

P2...993 mb deep-layered cyclone/upper trough centered over SE Canada is still shifting eastward into the western Atlantic. In the last 24 hrs...the surface center has weakened from 993 to 1008 mb while becoming stuck under the less-divergent axis of the upper trough...and the upper trough's eastern divergence is spinning up a new less-than-1004 mb depression east of Newfoundland that will likely. Meanwhile...1023 mb surface ridge over eastern North America remains supported by western upper convergence of the upper trough. Warm air advection ahead of the aforementioned 1008 mb and 1004 mb cyclones has amplfied the NE Atlantic upper rige into a full-fledged upper anticyclone.

P3...Upper vortex in the NE Atlantic has de-amplified into an upper trough. Upper convergence on the west side of the upper trough supports 1018 mb surface ridge transferring in the eastern Atlantic. After heading eastward toward Portugal in the previous discussion...the remnant surface gale of Rafael has turned on a more NE track in advance of a newer gale center (currently 996 mb) just to his west. The new gale appears to have spun up while taking advantage of split flow upper divergence between the upper trough and paragraph P2 NE Alantic upper anticyclone...and has a chance to become the dominant while absorbing ex-Rafael.

...TROPICAL BELT DISCUSSION...
P4...Upper ridge in the eastern tropical Atlantic persists. Pair of tropical waves WSW of the Cape Verde Islands continue to produce enhanced showers and t-storms under the favorable upper outflow of the upper ridge. However...this activity has become less organized since yesterday morning as the tropical waves slide into southerly vertical shear on the west side of the upper ridge.

Updated: 5:02 PM GMT on October 27, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #141A (Special Update)

By: NCHurricane2009, 8:50 PM GMT on October 24, 2012

...WEDNESDAY OCTOBER 24 2012...4:49 PM EDT...
Hurricane Sandy at high risk of rapid intensification before reaching eastern Cuba late tonight. All preparations in eastern Cuba should have been completed by this point as weather conditions will go downhill from this point forward.

Just before landfall in eastern Jamaica earlier today...Sandy intensified into a category 1 hurricane of 80 mph maximum sustained winds. Despite the landfall...visbile satellite imagery reveals a very impressive core and eye structure remaining intact. And with conditions remaining very favorable for intensification...their is a chance for rapid intensification into a category 2 (100 to 110 mph max sustained winds)...possibly even a category 3 (115 to 125 mph max sustained winds)...before the eye reaches eastern Cuba late this evening.

Return to full discussion #141 for an assessment on the rest of the Atlnatic tropics.

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2012 Atlantic Hurricane Season Birdseye Discussion #141

By: NCHurricane2009, 12:02 PM GMT on October 24, 2012

...WEDNESDAY OCTOBER 24 2012...8:15 AM EDT...
Tropical Storm Sandy moving northward toward Jamaica as expected...and is about to become a hurricane at any time now. Although Sandy has intensified over the last day...she has not rapidly intensified so far. Regardless...Sandy remains a significant heavy rain and wind threat to Jamaica...eastern Cuba...Haiti...and the Bahamas. See the Sandy special feature section below for additional details on this potentially severe situation. In the event Sandy begins to show signs of rapid intensification before I release my next full discussion...I will be releasing special updates.

Tropical depression nineteen has strengthened into Tropical Storm Tony in the last day. The new tropical storm is expected to stay over open waters. See the Tony special feature section for additional details.

A 1009 mb surface low WSW of the Cape Verde Islands...associated with the eastern of the two tropical waves in paragraph P4 of the tropical belt discussion...has become a little better organized under favorable upper winds as of 5 AM EDT this morning.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM SANDY...
Preparations for Sandy in Jamaica should have been completed by now with the storm expected to make landfall there later this morning. Under the guise of impact statement (b) in Figure 1...Haiti and the Dominican Republic can expect heavy rains with potential flash floods and mudslides...with the western half of Haiti getting some gusty winds as the impact swath in Figure 1 shows. Eastern Cuba and the Bahamas should finish preparations during the daylight hours of today...with conditions in these areas to deterorate later tonight and tomorrow.

Concerning the east coast of North America and Bermuda...tropical storm watches have been issued for SE Florida...but the impact info in Figure 1 suggests that SE Florida should at most see increased sea swells and rip currents on the coast. However...residents in SE Florida should be aware in case the storm hooks more leftward than expected in track. Their remains debate about the long-term solution of Sandy beyond the scope of the forecast track in Figure 1. Forecasts such as the one I present in Figure 1 are less threatening to the NE United States and Atlantic Canada...but moreso to Bermuda. The GFS and Euro models show a system hooking leftward as an intensifying non-tropical gale...with the Euro showing a strike to the NE United States...and the 00Z GFS showing a strike to Atlantic Canada.

Latest watches and warnings are found under the public advisory for Sandy at www.nhc.noaa.gov.

Track-wise for Sandy...she is tracking a bit faster to the north than I and the NHC previously thought...and she is tracking toward the east end of Jamaica more in alignment with my previous short-term solution than the NHC's previous short-term solution. Despite this...the previous NHC short-term solution will probably end up with less error than mine when evaluated because I showed a slower northward speed than the NHC's. I previosly predicted a track arcing from NNE to NNW around the curvature of an imagined upper vortex near the Isle of Youth of western Cuba. However...this feature did not quiet amplify into an upper vortex like I previously thought...so my updated forecast track in Figure 1 below shows a straight north track rather than an arcing track. This means I agree with the NHC track solution thru 11 PM Thu. 11 PM Thu continues to be coincident with when the GFS model shows the paragraph P2 SE US surface ridge N of Sandy at peak strength...so I agree with the slower NHC forecast track between 11 PM Thu and 11 PM Fri...but I am a hair faster than the NHC during this timeframe because this is also when that ridge weakens. Beyond 11 PM Fri...I continue to show an ENE track...creating a southward and more offshore bias with respect to NHC's solution...and also creating a track more threatening to Bermuda. I still agree with the ENE track because the GFS still creates a strong North America surface ridge on the convergent back side of the paragraph P1 upper troughing...and such a ridge would block progression toward North America. Instead...the system would get attracted toward the paragraph P2 deep-layered cyclone (which should be east of Sandy by the end of the 5-day forecast in Figure 1)...much like how during discussion #107 when Nadine got pulled ENE toward the ex-Isaac deep-layered cyclone. Because we had previously under-predicted Nadine's ENE acceleration in such a scenario...another reason I prefer to show my more ENE track in Figure 1.

Whether the non-tropical remnant of Sandy continues ENE out to sea...or whether she hooks leftward toward the NE US or Atlantic Canada depends on how much the North America surface ridge hugs the storm to the north...and depends on how interaction she has with the paragraph P1 upper trough. Such an interaction requires that Sandy is close enough or aligns with the paragraph P1 upper trough such that she takes maximum advantage of the eastern divergence of the upper trough and intensifies non-tropically. Cool air advection on her back side in turn amplifies the upper trough into an upper vortex that would whirl her NW. The Euro model shows a "perfect storm" scenario with a non-tropical Sandy slamming into the NE US at an awesome 938 mb...but such a perfect scenario requires such perfect alignment with the paragraph P1 upper trough. Statistics are usual against perfect storm scenarios...so I am not buying into this solution at this time.

Intensity-wise for Sandy...it looks like the aformentioned cut-off upper trough near the Isle of Youth of western Cuba may have disrupted Sandy's NW upper outflow a bit more than I thought...so she has not strengthened as quickly as I previously showed. Therefore my new intensity forecast in Figure 1 at most shows a category 2 hurricane (100 mph max winds) rather than a category 3 hurricane (115 mph max winds). Due to her currently impressive satellite apperance and excellent upper outflow over her south and east quadrants...I show a strengthening rate similar to my previous...coordinating with land disruptions from Jamaica and eastern Cuba while taking into account the updated track forecast in Figure 1. I begin weakening Sandy toward the end of the forecast...coincident with when the 00Z GFS shows upper SW shearing winds increasing ahead of the paragraph P1 upper trough. I agree with the transition to non-tropical by 120 hrs as Sandy should be well embedded within the eastern divergence region of the upper trough when using my track forecast and the 00Z GFS upper wind forecast.


Figure 1: Tropical Storm Sandy Forecast

My impact swath initialization in Figure 1 is the same size as my previous. This swath size continues to include Sandy's central-dense overcast and adjacent spiral band to the east...both features which have not changed in size since my previous update. This is where I believe Sandy will establish her worst impacts...although this swath is larger than the tropical storm wind radius shown in the 5 AM EDT NHC advisory. Satellite imagery shows that the eastern divergence of the cut-off upper trough near the Isle of Youth has expanded the moisture field hundreds of miles to the north and east of Sandy itself...which is why impact statement (b) in Figure 1 is written. Such far-reaching rain bands are less likely on the west side of Sandy due to the suppression by the cut-off upper trough near the Isle of Youth...followed by suppression from the incoming paragraph P1 upper trough. These suppressive effects are also why I maintain an east bias with my impact swath when compared to my forecast track.

...SPECIAL FEATURE...TROPICAL STORM TONY...
Although previously I was correct in showing a faster track with this tropical cyclone...my northward bias in my previous forecast did not happen...instead Tony following the path shown by the NHC track forecast. It appears I was giving too much credence to the 1018 mb ridge east of Tony shown in the above atmo chart and mentioned in paragraph P3. Although their is still an ever-so-slight left angle in Tony's current track with respect to the NHC forecast track...I am avoiding temptation for showing any northward bias this time around...especially as the previous NHC track path did very well...and with the current NHC track path a continuation of the previous. This is also fairly consistent with the 00Z GFS track forecast...which shows Tony continuing ENE while steered by the south side of the paragraph P2 cyclone.

Intensity-wise...I did better than the NHC did 24 hrs ago...with the NHC at that time showing too high of an intensity forecast...and my intensity forecast being much closer to what happened in reality. However...my weakish intensity forecast depended on my previous northward-biased track forecast which hurtled Tony into the westerly shear of the paragraph P2 upper trough. Instead...Tony has better followed the more south NHC track forecast such that he stayed closer in touch with his favorable warm core upper anticyclone...so as to why he followed my more weakish intensity forecast is more dumb luck to me than something that makes sense. At this point...the shear from the paragraph P2 upper trough will be on the increase regardless of how far north or south Tony will be...because the upper trough is nearing and shoving off Tony's favorable warm core upper anticyclone and t-storm canopy. I forecast no strengthening nor weakening as a balance between the unfavorable shear and favorable eastern divergence of the upper trough as Tony becomes non-tropical.


Figure 2: Forecast for Tropical Storm Tony

Impact swath in Figure 2 is based on the size of the t-storm canopy seen in infrared satellite...and extrapolating that along the forecast track. The impact swath is smaller than previous despite Tony being stronger than previous...because Tony has tightened up a bit while strengthening.

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system in the mid-latitudes continues entering from SW Canada and the western US in the upper-left corner of the above atmo chart. In the upper-levels...the system has two impulses...with the eastern divergence of the first upper trough (located over the Great Lakes and Ohio Valley) driving a 1017 mb frontal depression moving into the NE US. Vast divergence east of the second upper trough driving a few frontal depressions across the western and central US. Low-level warm air advection ahead of the frontal depressions supports an upper ridge persisting over the central US...albeit this upper ridge is now broken by the aformentioned Ohio Valley upper trough.

P2...987 mb deep-layered cyclone/upper trough centered over SE Canada is still shifting eastward into the western Atlantic. In the last 24 hrs...the surface center has weakened from 987 to 993 mb while becoming stuck under the less-divergent upper vortex of the upper trough. In the last two days...southern portion of the upper trough has cut-off over the NW Caribbean Sea in the vicinity of the Isle of Youth of western Cuba (see Sandy special feature section for how this upper trough continues interacting with Sandy). Upper convergence on the west side of the NW Caribbean cut-off upper trough supports increasingly dry air in Gulf of Mexico. Meanwhile...1023 mb surface ridge over the SE US remains supported by western upper convergence of the deep-layered cyclone's upper trough. Warm air advection ahead of the deep-layered cyclone continues supporting an upper ridge now shifting from the central to the NE Atlantic.

P3...Upper vortex in the NE Atlantic remains amplified...thanks to cool air advection on the back side of the remnant gale of Rafael. Upper convergence on the west side of the upper vortex supports dry air and 1018 mb surface ridge transferring from the central to the eastern Atlantic. After being centered just north of the Azores in the previous discussion...the remnant surface gale of Rafael has turned on a more easterly track toward Portugal in deep-layer W flow on the south side of the upper vortex and north of the aforementioned 1018 mb ridge. The gale has weakened from 990 to 994 mb in the last 24 hours while beneath the non-divergent upper vortex.

...TROPICAL BELT DISCUSSION...
P4...Upper ridge in the eastern tropical Atlantic persists. Tropical wave W of the Cape Verde Islands in the previous discussion...and tropical wave over and south of the Cape Verde Islands in the previous discussion...are both continuing westward in the waters WSW of the islands this morning. While both tropical waves are under the favorable low shear and upper outflow of the upper ridge...so far no signs of organizing t-storm activity except for a 1009 mb low near 32.5W-10N that has very recently become a little better organized.

Updated: 6:25 AM GMT on October 25, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #140

By: NCHurricane2009, 7:19 AM GMT on October 23, 2012

...TUESDAY OCTOBER 23 2012...3:20 AM EDT...
Tropical disturbance Invest 99-L in the central Caribbean Sea has become tropical depression eighteen...and then Tropical Storm Sandy...in the last 24 hours. Sandy has a risk of strengthening rapidly...and is a threat to Jamaica...eastern Cuba...Haiti...and the Bahamas. See the Sandy special feature section below for additional details on this potentially severe situation. In the event Sandy begins to show signs of rapid intensification before I release my next full discussion...I will be releasing special updates.

Disturbance Invest 90-L in the open Atlantic...associated with an upper vortex interacting with a tropical wave...has organized into tropical depression nineteen in the last 24 hours. The new tropical cyclone is expected to stay over open waters. See the tropical depression nineteen special feature section for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM SANDY...
Central Caribbean disturbance Invest 99-L has put on an impressive show over the last 24 hours while evolving into Tropical Storm Sandy of 45 mph max winds as of 11 PM EDT. Because of the potential for Sandy to reach severe intensity...it is paramount interests in Jamaica...Haiti...eastern Cuba...and the Bahamas to carefully monitor Sandy...and under the guidance of local officials begin preparations for a severe storm if and when your area undergoes a watch or warning. Under the guise of impact statement (b) in Figure 1 below...the Dominican Republic may also get heavy rains from Sandy thanks to her eastern outer rain bands. Jamaica and Haiti are currently under a tropical storm watch. Latest watches and warnings are found under the public advisory for Sandy at www.nhc.noaa.gov.

Track-wise for Sandy...comparing the 200 mb wind barbs in the above atmo chart with the 18Z GFS model shows that the paragraph P2 cut-off upper trough is both more amplified and further east than expected...and based on its current amplitude I expect it to evolve into a cut-off upper vortex just east of the Isle of Youth of western Cuba. Computer models agree on an initial NNE trajectory toward Jamaica...but since this trajectory has yet to start as seen on satellite animation...my forecast track is a little slower than the NHC's from the get-go as seen in Figure 1. Since the computer models accelerate Sandy NNE in response to the amplifying cut-off upper trough...and since the upper trough is already more amplified than the models are showing...my forward pace catches up to the NHC forecast...but I am initially to the right of the NHC to account for my aforementioned observation of the upper trough being a bit further east than shown in the models. On my expectation that the cut-off upper trough evolves into an upper vortex just east of the Isle of Youth...by 72 hrs (11 PM Thu) and 96 hrs (11 PM Fri) I hook Sandy northward then NNW around such an upper vortex such that I develop a left bias with respect to NHC by that time. A catalyst for a more NNW track by 72 hrs is that the 18Z GFS shows the paragraph P2 SE US surface ridge N of Sandy at peak strength by that time (the strength of the ridge also makes me keep Sandy south of the NHC's forecast by 72 hrs). In advance of the paragraph P1 weather system...this surface ridge quickly erodes by 96 and 120 hrs in the 18Z GFS...becoming replaced by a strong surface ridge across much of North America that blocks Sandy from continuing NNW toward the US. Rather...the 18Z GFS shows Sandy hooking more eastward while attracted to the paragraph P2 cyclone which is shown to be east of Sandy by that time...and my forecast track by 120 hrs agrees with this general idea presented by 18Z GFS.

Intensity-wise for Sandy...despite the aforementioned observation of a possible cut-off upper vortex forming near the Isle of Youth...Sandy does not seem bothered as evidenced by good upper outflow in her NW quadrant. More disconcerting is her ever-improving satellite appearance as the strong t-storm clouds continue to evolve into a spiral band structure with a central-dense-overcast (CDO). Moreover...Sandy should be over very warm sea-surface temps thru the forecast period...and the 18Z GFS for the first 96 hrs suggests excellent upper outflow over the east half of the storm...probably enough to compensate for whatever outflow blockage the Isle of Youth upper vortex may bring. In addition...some of the most intense October Atlantic tropical cyclones are those that originate in the Caribbean much like Sandy. Therefore my intensity forecast in Figure 1 is a lot more bullish than the 11 PM NHC's. By 24 hrs (11 PM Tue)...I bring Sandy into a hurricane (75 mph max winds)...and then I briskly strengthen Sandy into a major hurricane (115+ mph max winds)...coordinating my major hurricane intensity forecast with land disruptions from Jamaica and eastern Cuba. I finally allow Sandy to weaken below major hurricane force by 120 hrs as the 18Z GFS shows the upper anticyclonic outflow over Sandy transition into upper SW shearing winds ahead of the paragraph P1 upper trough.


Figure 1: Tropical Storm Sandy Forecast


Figure 2: Impact swath initialization in Figure 1 based on 0415Z Sandy satellite image as of 0415Z this morning

My impact swath initialization in Figure 1 is based on the red circled area in Sandy's 0415Z infrared satellite image shown in Figure 2. This red circled area includes Sandy's central-dense overcast and adjacent spiral band where I believe Sandy will establish her tropical storm and hurricane force winds as well as her heaviest rain. As seen in Figure 2...their are also sprawling rain bands on the east side of Sandy and outside the swath...which is why impact statement (b) in Figure 1 is written. Such far-reaching rain bands are less likely on the west side of Sandy due to the suppression by the developing upper vortex near the Isle of Youth. The red-circled area in Figure 2 has an east bias with respect to the current location of the storm center...an effect also due to the upper vortex. Since I expect this upper vortex to be present thru much of the forecast period...I maintain this east bias with my impact swath when compared to my forecast track.

...SPECIAL FEATURE...TROPICAL DEPRESSION NINETEEN...
The surface tropical wave/low centered near 50W-20N in the previous discussion...formerly known as Invest 90-L...has spun up into tropical depression nineteen within the last 24 hrs. Its t-storm latent heat release has punched out a good chunk of the upper vortex above into a favorable warm core upper anticyclone.

The new tropical depression is tracking northward while in southerly flow ahead of the paragraph P2 deep-layered cyclone. Immediately...my forecast in Figure 3 below is in disagreement with the NHC's and the GFS model...showing a more north and faster track. This is because the NHC and GFS I believe have under-estimated how fast the tropical depression is already tracking to the north...using the NHC recorded storm track which in Figure 3 shows only 6 hours worth of northward motion...and using current infrared satellite which shows the center already approaching 25N latitude before sunrise. I do agree with the hook to the right as the paragraph P2 deep-layered cyclone barges in from the NW...but my northward bias in track means that I predict the depression to hit westerly shearing winds from the paragraph P2 upper trough sooner...and merge with the cold front of the cyclone sooner. Therefore my intensity forecast in Figure 3 is quiet weaker than the NHC's...as I forecast the system to barely become a tropical storm of 40 mph max winds before the westerly shear hits it. I do not show the system weakening under shear as I believe it has potential to interact with the eastern divergence of the paragraph P2 upper trough as it merges with the cold front.


Figure 3: Forecast for Tropical Depression Nineteen

Impact swath in Figure 3 is based on the sprawling field of scattered t-storm clouds seen on infrared satellite. This field of clouds is already biased to the right of the storm center from the incoming westerly shear...and I extrapolate this nature of the cloud field along my forecast track to create the impact swath.

...MID-LATITUDES DISCUSSION...
P1...Next surface frontal system in the mid-latitudes continues entering from SW Canada and the western US in the upper-left corner of the above atmo chart. In the upper-levels...the system has two impulses...with the western convergence of the first upper trough driving a 1023 mb ridge over southern Manitoba...and vast divergence east of the second upper trough driving a few frontal depressions across the western and central US. Low-level warm air advection ahead of the frontal depressions supports an upper anticyclone that has moved from Hudson Bay into the east coast of Canada...and supports an upper ridge persisting over the central US.

P2...994 mb deep-layered cyclone/upper trough centered over SE Canada is shifting eastward into the western Atlantic. In the last 24 hrs...the surface center has strengthened from 994 to 987 mb while tapping into split flow divergence between the upper vortex of the upper trough and paragraph P1 upper anticyclone on the east coast of Canada. Southern portion of the upper trough has cut-off over the NW Caribbean Sea. Upper convergence on the west side of the deep-layered cyclone and cut-off upper trough supports Gulf of Mexico and W Atlantic dry air...as well as surface ridge (currently 1023 mb) over the SE US. Warm air advection ahead of the deep-layered cyclone supports an upper ridge shifting into the central Atlantic.

P3...Upper trough in the NE Atlantic has amplified into an upper vortex stacked over the surface gale that is the remnant of Rafael...thanks to cool air advection on the back side of the remnant gale. Upper convergence on the west side of the upper vortex supports dry air and 1016 mb central Atlantic surface ridge. The remnant surface gale of Rafael continues on a southeast track in deep-layer NW flow on the back side of the upper vortex and east of the aforementioned 1016 mb ridge...and was centered just north of the Azores as of 1800Z this evening. The gale has weakened from 988 to 990 mb in the last 24 hours while beneath the non-divergent upper vortex.

P4...Weakening east Atlantic surface ridge...mentioned in paragraph P4 of the previous discussion...is becoming assimilated into the 1016 mb ridge mentioned in paragraph P3 above...and therefore is no longer a distinct feature.

...TROPICAL BELT DISCUSSION...
P5...Upper ridge in the eastern tropical Atlantic persists. Tropical wave W of the Cape Verde Islands in the previous discussion is seeing its t-storm activity enhanced by the outflow of the upper ridge...but so far has no signs of organization. Another tropical wave has recently exited from Africa...currently located over and south of the Cape Verde Islands.

Updated: 11:54 PM GMT on October 23, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #139

By: NCHurricane2009, 3:22 AM GMT on October 22, 2012

...SUNDAY OCTOBER 21 2012...11:22 PM EDT...
Tropical disturbance Invest 99-L in the central Caribbean Sea has not gotten any better organized in the last 24 hours. However...tropical cyclone formation from this system is still likely. See the Invest 99-L special feature section below for details.

Disturbance Invest 90-L in the open Atlantic...associated with an upper vortex interacting with a tropical wave...has potential for subtropical or tropical cyclone formation in the next 24 hours. See Invest 90-L special feature section for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1924Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...CARIBBEAN DISTURBANCE INVEST 99-L...
The disturbance continues to have a broad surface low consisting of a tropical wave entering the central Caribbean and a western Caribbean surface trough. In the upper-levels...the disturbance continues to be ventilated by the outflow of an east-west upper ridge. The focal point of this system continues to be the tropical wave...but the system has become less organized in the last day while the western Caribbean surface trough had flared up. Perhaps the surface trough had taken away from the focal point of the disturbance...but with the surface trough removed from TAFB maps by 1200Z...this system may proceed to re-organize and develop into a tropical cyclone.

Their continues to be two possible solutions as follows...

The eastern solution is for gradual tropical cyclone formation while the east US surface ridge in paragraph P2 builds to the north...and a cut-off upper trough from the paragraph P2 upper trough amplifies to the NW (thanks to equally amplifying paragraph P1 upper ridge). In such a scenario...tropical cyclone intensity is highly uncertain...as the tropical cyclone either suffers from SW vertical shear delivered by the cut-off upper trough...or thrives under the upper ridge...depending on exactly where the surface center consolidates. In such a solution...it appears the tropical cyclone would be vertically coupled enough to be steered by the cut-off upper trough such that the tropical cyclone first drifts NNE toward Jamaica...eastern Cuba...the eastern Bahamas...and western Hispaniola while the tropical cyclone is trapped by conflicting steering between the surface ridge and cut-off upper trough. Afterwards the surface ridge gets knocked out in between the paragraph P2 cyclone and paragraph P1 surface frontal system...sending the tropical cyclone ENE into the open Atlantic.

The more western solution is a track toward Jamaica...Cuba...the Cayman Islands...the western Bahamas...and southeastern Florida. Computer models show a stronger tropical cyclone when depicting this western solution. This solution would verify if the cut-off upper trough is less influential. A less influential cut-off upper trough means less NE steering and more NW steering from the surface ridge...and also means a stronger tropical cyclone less affected by vertical shear from the upper trough.

The GFS model initially switched from the eastern to the western solution...but now shows a solution that is a compromise between these extremes. The CMC and Euro models have joined the current middle-ground solution of the GFS. The NOGAPS currently agrees with the western solution. Residents in Hispaniola (Haiti and the Dominican Republic)...Jamaica...Cuba...the Cayman Islands...the Bahamas...and southeastern Florida are urged to keep tabs on this developing situation until it is clearer which solution will play out.

...SPECIAL FEATURE...OPEN ATLANTIC UPPER VORTEX DISTURBANCE INVEST 90-L...
In the Atlantic tropics east of the Lesser Antilles...cut-off upper vortex persists. The tropical wave exiting the area and moving toward the Lesser Antilles has dissipated as of 0600Z TAFB analysis. The tropical wave/low near 45W-17N in the previous discussion is now the dominant surface feature of this system while centered near 50W-20N tonight. This surface low has become better organized with a small t-storm cluster enhanced by split flow upper divergence between the NW quad of the upper vortex and SW quad of the paragraph P2 central Atlantic upper ridge. Based on this organization...I forecast a fairly high chance of subtropical or tropical cyclone formation in the next 24 hours. Since the aforementioned split flow upper divergence supporting the surface low is created by both the cold core upper vortex and adjacent warm core upper ridge...subtropical or tropical status will be dependent upon whether more credit is given to the upper vortex or upper ridging. Such a tropical or subtropical system would first track west on the north side of the upper vortex and south of the paragraph P3 1016 mb ridge...then track northward by 48 hours while getting swept into the paragraph P2 cyclone's cold front coming in from the west. Such a forecast track keeps this system well away from land areas and over open waters.

...MID-LATITUDES DISCUSSION...
P1...Next surface frontal system and upper trough in the mid-latitudes continues entering from SW Canada and the western US in the upper-left corner of the above atmo chart. Low-level warm air advection ahead of the frontal system supports an upper anticyclone over Hudson Bay and upper ridge shifting into the central US.

P2...1001 mb deep-layered cyclone/upper trough centered over the Great Lakes in the previous discussion has shifted into SE Canada. The surface center has strengthened from 1001 to 994 mb while tapping into divergence on the east side of the upper trough. Upper convergence on the west side of the deep-layered cyclone supports Gulf of Mexico and W Atlantic dry air...as well as surface ridge (currently 1021 mb) over the eastern US. Warm air advection ahead of the deep-layered cyclone supports an upper ridge shifting from the western to the central Atlantic.

P3...Upper trough in the vicinity of southern Greenland has shifted into the NE Atlantic. Western convergence of the upper trough supports dry air and 1016 mb central Atlantic surface ridge. The remnant surface gale of Rafael continues on a southeast track in deep-layer NW flow on the back side of the upper trough and east of the aforementioned 1016 mb ridge. The gale has weakened from 979 to 988 mb in the last 24 hours while beneath the non-divergent upper trough axis.

P4...Upper trough and surface frontal system entering western Europe in the previous discussion has exited the picture...except for a 1011 mb surface low over NE Spain in the upper-right corner of the above atmo chart. Western convergence of this upper trough formerly supported what is now a weakening surface ridge in the central and eastern Atlantic. This surface ridge is currently weakening in upper divergence ahead of the paragraph P3 upper trough.

...TROPICAL BELT DISCUSSION...
P5...Large-sized upper ridge across the eastern Atlantic has eroded out of the subtropical latitudes due to the paragraph P3 upper trough. What is left of the upper ridge in the tropical latitudes is enhancing the upper outflow of a tropical wave W of the Cape Verde Islands that has been added to TAFB maps as of 1800Z.

Updated: 3:23 AM GMT on October 22, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #138

By: NCHurricane2009, 9:54 PM GMT on October 20, 2012

...SATURDAY OCTOBER 20 2012...6:00 PM EDT...
Tropical cyclone formation in association with a tropical wave interacting with an upper ridge appears to be occurring ahead of schedule in the central Caribbean Sea. The disturbance has been organizing...surface pressures are falling...and it has been recently upgraded to disturbance Invest 99-L. See Invest 99-L special feature section below for further details on this developing situation.

As mentioned in special update #137A...we are also monitoring disturbed weather in the central open Atlantic...associated with an upper vortex interacting with tropical waves passing by. This disturbed weather has recently been upgraded to Invest 90-L. Although their is presence of surface vorticity in the area...it is not well-organized. However...given the simultaneous presence of favorable upper winds...I have upgraded this system to a special feature. See Invest 90-L special feature section for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1329Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...CARIBBEAN DISTURBANCE INVEST 99-L...
At the surface...the eastern Caribbean tropical wave in paragraph P5 of previous discussion #137 has combined with western Caribbean/western Cuba surface troughing in paragraph P2 of previous discussion #137...resulting in a large surface tropical low across the Caribbean. In the upper-levels...east Caribbean upper ridge in paragraph P4 of previous discussion #137 and SE Mexico upper ridge in paragraph P1 of previous discussion #137 have combined into a singular upper ridge whose upper outflow is ventilating the system.

The most impressive response to the favorable upper outflow has been toward where the aforementioned surface tropical wave was located this afternoon. This location is in the Caribbean waters south of Haiti...where the t-storms are most concentrated and their are signs of curved cloud bands collecting around observed surface pressure falls. In the intro statement of previous discussion #137...we had expected possible tropical cyclone formation from this area by 120 hours as of that writing...which is now 84 hours as of this writing. Based on the level of organization on satellite...tropical cyclone formation could easily occur sooner than this timing.

Eastern solutions such as the GFS model first show gradual tropical cyclone formation while the SE US surface ridge in paragraph P2 builds to the north...and a cut-off upper trough from the paragraph P2 upper trough amplifies to the NW (thanks to equally amplifying paragraph P1 upper ridge). In such a scenario...tropical cyclone intensity is highly uncertain...as the tropical cyclone either suffers from SW vertical shear delivered by the cut-off upper trough...or thrives under the upper ridge...depending on exactly where the surface center consolidates. In the GFS solution...it appears the tropical cyclone is vertically coupled enough to be steered by the cut-off upper trough such that the tropical cyclone first drifts NNE toward Jamaica...eastern Cuba...the eastern Bahamas...and western Hispaniola while the tropical cyclone is trapped by conflicting steering between the surface ridge and cut-off upper trough. The long-range GFS solution then knocks out the surface ridge in between the paragraph P2 cyclone and paragraph P1 surface frontal system...sending the tropical cyclone ENE into the open Atlantic.

Solutions such as the current CMC model show a more western track toward Jamaica...Cuba...the Cayman Islands...the western Bahamas...and southeastern Florida. The CMC model also depicts a stronger tropical cyclone than GFS. A solution such as the CMC would verify if the cut-off upper trough is less influential. A less influential cut-off upper trough means less NE steering and more NW steering from the surface ridge...and also means a stronger tropical cyclone less affected by vertical shear from the upper trough.

Residents in Hispaniola (Haiti and the Dominican Republic)...Jamaica...Cuba...the Cayman Islands...the Bahamas...and southeastern Florida are urged to keep tabs on this developing situation until it is clearer which solution will play out.

...SPECIAL FEATURE...OPEN ATLANTIC UPPER VORTEX DISTURBANCE INVEST 90-L...
In the Atlantic tropics east of the Lesser Antilles...cut-off upper vortex mentioned in paragraph P6 of previous discussion #137 persists. The tropical wave interacting with the upper divergence on the east side of the upper vortex...also mentioned in the previous discussion...is moving westward toward the Lesser Antilles and exiting this area as shown in Figure 1 below and in the above atmo chart. The t-storm cluster sheared-off from the exiting tropical wave persists in split flow upper divergence on the NE quad of the upper vortex. The split upper flow...shown in Figure 1...is the result of flow whirling around the cold core upper vortex splitting with anticyclonic flow around the paragraph P2 W Atlantic upper ridge and around the paragraph P5 upper ridge. 1800Z ASCAT pass of surface winds reveals possible new surface low spinning up near 48W-20N while taking advantage of aforementioned split flow upper divergence. In addition...yet another tropical wave with 1012 mb low near 45W-17N is adding to the t-storm activity with its surface convergence. Although the 1012 mb low is also defined as a swirl in visible satellite imagery in Figure 1 and the ASCAT pass in Figure 2...the 1012 mb low is less-likely to develop due to SW vertical shear from the upper vortex as shown in Figure 1. As shown in the above atmo chart...the 1012 mb low/tropical wave was added within TAFB maps within the last 30 hours...and was not added beforehand due to its poor definition.


Figure 1: 1800Z synopsis of disturbance Invest 90-L using visible satellite imagery. Blue is upper air analysis...red is surface analysis.


Figure 2: 1800Z ASCAT of surface winds. Red Ls mark the location of the 1012 mb surface low near 45W-17N...and possible new surface low near 48W-20N.

I forecast possible subtropical or tropical cyclone formation in the next 48 hours from the new surface low spinning up near 48W-20N. Since the aforementioned split flow upper divergence supporting this new surface low is created by both the cold core upper vortex and adjacent warm core upper ridging...subtropical or tropical status will be dependent upon whether more credit is given to the upper vortex or upper ridging. Such a tropical or subtropical system would first track west on the north side of the upper vortex and south of the paragraph P3 1029 mb ridge...then track northward by 72 hours while getting swept into the paragraph P2 cyclone's cold front coming in from the west. Such a forecast track keeps this system well away from land areas and over open waters.

...MID-LATITUDES DISCUSSION...
P1...Next surface frontal system and upper trough in the mid-latitudes is entering from SW Canada and the western US in the upper-left corner of the above atmo chart. Low-level warm air advection ahead of the frontal system supports upper ridge building across the western US.

P2...994 mb deep-layered cyclone/upper trough centered over Wisconsin in the previous discussion continues shifting eastward. While moving eastward across the Great Lakes...the surface center has weakened from 994 to 1001 mb in the last 36 hours due to lack of divergence beneath the upper vortex of the upper trough. Upper convergence on the west side of the deep-layered cyclone supports surface ridge (currently 1015 mb) that has moved from the western to the SE US in the last 36 hrs. Meanwhile...warm air advection ahead of the deep-layered cyclone supports an upper ridge that has built in the W Atlantic.

P3...Upper trough and surface gale activity in the vicinity of southern Greenland has undergone complex evolution in the last 36 hrs. The upper trough has absorbed secondary W Atlantic upper trough mentioned in paragraph P1 of previous discussion #137. NW Atlantic/SE Canada surface ridge supported by western convergence of absorbed secondary upper trough has intensified further to 1029 mb. The remnant surface gale of Rafael made an initial NW turn toward southern Greenland while absorbing the 977 mb gale supported by the eastern divergence of the upper trough. After nearing southern Greenland...the remnant gale of Rafael has reversed to a southeast track while entering deep-layer NW flow on the back side of the upper trough and east of the aforementioned 1029 mb ridge. Surface trough ENE of Bermuda...left behind by cold front extending SW from Rafael in the previous discussion...was analyzed as a weak 1017 mb low as of 1200Z TAFB analysis.

P4...Upper trough and surface frontal system entering western Europe in the previous discussion has exited the picture...except for a surface front extending into NW Africa seen in the upper-right corner of the above atmo chart. Western convergence of this upper trough formerly supported what is now a weakening 1021 mb ridge in the central and eastern Atlantic. This surface ridge is currently weakening in upper divergence ahead of the paragraph P3 upper trough.

...TROPICAL BELT DISCUSSION...
P5...Large-sized central Atlantic upper ridge in paragraph P4 of the previous discussion...and E tropical Atlantic upper ridge in paragraph P6 of the previous discussion...have merged into one large upper ridge across the tropical and subtropical eastern Atlantic.

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2012 Atlantic Hurricane Season Birdseye Discussion #137A (Special Update)

By: NCHurricane2009, 10:10 PM GMT on October 19, 2012

...FRIDAY OCTOBER 19 2012...6:10 PM EDT...
Two Atlantic tropical cyclones are possible this upcoming week...

In addition to potential Caribbean tropical cyclone formation discussed in paragraph P5 of discussion #137...their is also potential for tropical cyclone formation in the central open Atlantic in association with a tropical wave interacting with an upper vortex (paragraph P6 of discussion #137). Although I had seen computer model support for a central open Atlantic tropical cyclone as of the previous discussion...I had not mentioned it as I was not sure which system the models were picking up on.

Both the Caribbean disturbance and the open Atlantic disturbance have been introduced into the National Hurricane Center Tropical Weather Outlook. I will be assessing whether or not I believe either of these areas have a high risk of eventual tropical cyclone formation. If I believe so...I could be introducing either or both as special features in my next full blog update. In the meantime...return to full discussion #137 for an assessment on the rest of the Atlantic tropics.

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2012 Atlantic Hurricane Season Birdseye Discussion #137

By: NCHurricane2009, 11:04 AM GMT on October 19, 2012

...FRIDAY OCTOBER 19 2012...7:10 AM EDT...
Although the Atlantic tropics are currently calm....their is increasing computer model support for tropical cyclogenesis in the Caribbean Sea by 120 hours. See paragraph P5 for statement on this situation.

GOES-E satellite has finally been repaired. Therefore...the view in the two birdseye charts below no longer requires repair.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0731Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Surface frontal system in the mid-latitude westerlies continues marching eastward across North America with a pair of upper troughs. The first upper trough with embedded upper vortex has arrived into the central US. 983 mb cyclone over NW Minnesota in the previous discussion has whirled SE into a position beneath the upper vortex...resulting in a 994 mb deep-layered cyclone centered over Wisconsin this morning. Strong convergence on the west side of the deep-layered cyclone supports building surface ridge across the western US with 1024 mb to 1016 mb centers. Upper ridge persists across SE Mexico in relatively higher pressures south of the deep-layered cyclone. Secondary upper trough of this system has moved from the eastern US into the W Atlantic in the last 24 hrs..its western convergence supporting 1025 to 1024 mb ridge over the NW Atlantic and SE Canada.

P2...Upper trough and surface frontal system over the western Atlantic in the previous discussion has advanced ENE into the north Atlantic high seas in the vicinity of southern Greenland. Western convergence of the upper trough formerly supported a surface ridge over E Canada...but now this ridge is supported by western convergence of secondary upper trough in paragraph P1. However...eastern divergence of this upper trough continues supporting a strong surface frontal depression that has intensified from 989 mb to 977 mb while moving ENE past this southern tip of Greenland in the last 24 hours. Surface cold front of this depression continues to have the remnant gale of Rafael also racing ENE across the north Atlantic high seas. Eastern divergence of this upper trough also supports the remnant of Rafael...so expect Rafael to continue its slow rate of weakening. Rafael may soon lose its identity if it merges with aforementioned 977 mb center. Cold front in which Rafael is embedded extends far to the southwest...and in the last 48 hours has left behind surface troughs over the western Caribbean and near western Cuba....as well as another surface trough ENE of Bermuda. The surface trough ENE of Bermuda is currently supported by eastern divergence of secondary upper trough mentioned in paragraph P1.

P3...Upper trough continues eastward across the NE Atlantic and is making landfall in western Europe this morning. Western convergence of the upper trough formerly supported what is now the 1024 mb surface ridge in the eastern Atlantic...but this surface ridge is now stacked with upper ridge mentioned in paragraph P4 to make a deep-layered ridge. Meanwhile...eastern divergence of this upper trough supports a surface low and associated cold front continuing to advance eastward across western Europe and Morocco.

...TROPICAL BELT DISCUSSION...
P4...Large-sized central Atlantic upper ridge extending into the eastern Caribbean has split into two this morning. One center is vertically stacked with 1024 mb east Atlantic surface ridge in paragraph P3...resulting in a deep-layered ridge. The other center remains in the eastern Caribbean just south of Hispaniola (Haiti and the Dominican Republic).

P5...Tropical wave crossing the southern Lesser Antilles in paragraph P5 of previous discussion #136 is now in the eastern Caribbean. Along with upper outflow enhancement from paragraph P4 upper ridge center south of Hispaniola...the tropical wave is producing scattered t-storm clouds across the eastern Caribbean Sea this morning. By 120 hours...computer models agree that a broad tropical low or tropical cyclone will spin up in the central Caribbean region. Not sure at this time if it is this tropical wave that the models are developing. If not...perhaps it is the tropical wave in paragraph P6...which will travel westward and eventually also interact with the favorable upper ridge center south of Hispaniola.

P6...In the tropical Atlantic east of the Lesser Antilles...cut-off upper vortex persists. Western of the two tropical waves in the vicinity has escaped the influence of the upper vortex...and has its own paragraph (see paragraph P5 above). The eastern of the two tropical waves is producing enhanced t-storm activity while interacting with the eastern divergence of the upper vortex. However...this t-storm cluster is sheared off the wave by the upper westerly winds across the south side of the upper vortex. Meanwhile...E tropical Atlc upper ridge persists in relatively higher pressures E of the upper vortex.

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2012 Atlantic Hurricane Season Birdseye Discussion #136

By: NCHurricane2009, 7:55 AM GMT on October 18, 2012

...THURSDAY OCTOBER 18 2012...3:55 AM EDT...
Hurricane Rafael becomes extratropical (non-tropical) within the last 24 hours while accelerating east-northeast into the north Atlantic high seas. Although no longer a special feature on this blog...non-tropical Rafael is producing heavy rains...high winds...and rough seas...and therefore remains a marine threat. See paragraph P2 for statement on non-tropical Rafael.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Next surface frontal system in the mid-latitude westerlies continues marching eastward across North America with a pair of upper troughs. The first upper trough has entered from the top-left of the atmo chart while highly amplified with an embedded upper vortex. Strong convergence on the west side of the upper trough supports building surface ridge across the western US...while strong divergence on the east side of the upper trough is driving a strong frontal cyclone of 983 mb centered near the NW corner of Minnesota. Low-level southerlies ahead of the cyclone are in directional shear with respect to upper-level westerlies. The shear (along with instability) is supporting severe weather and tornadoes across Mississippi this early morning (vist www.nws.noaa.gov for any severe weather watches or warnings that may be required for this system across the southeast US over the next 24 hours). Second upper trough has moved from the central to the eastern US in the last 24 hrs..and its eastern divergence is producing cloudiness just offshore of the eastern US. Meanwhile...upper ridge persists across SE Mexico in relatively higher pressures south of both upper troughs.

P2...Upper trough and surface frontal system continues advancing into the western Atlantic. Western convergence of the upper trough supports 1015 to 1016 mb ridge over eastern Canada and offshore of SE US. Eastern divergence of the upper trough supports 989 mb frontal depression that has moved offshore from eastern Canada and headed for southern Greenland. Surface cold front of this depression has overspread former Hurricane Rafael in the last 24 hours as he accelerates ENE into the north Atlantic high seas. Eastern divergence of this upper trough also supports Rafael...so expect Rafael to only slowly weaken over the next several hours. Therefore...vigorous ex-Rafael remains a marine threat. Cold front in which Rafael is embedded extends toward the western Caribbean and western Cuba...where it leaves behind a pair of surface troughs.

P3...Upper trough continues advancing away from Greenland while continuing east across the NE Atlantic. Western convergence of the upper trough supports 1028 mb surface ridge that is moving from the central to the eastern Atlantic. Meanwhile...eastern divergence of the upper trough supports relatively new surface frontal low that has entered Europe from the British Isles. Cold front extending from the surface low extends to northern Canary Islands.

...TROPICAL BELT DISCUSSION...
P4...Large-sized central Atlantic upper ridge continues to extend into the SE half of the Caribbean Sea.

P5...In the tropical Atlantic east of the Lesser Antilles...cut-off upper vortex persists. Pair of tropical waves in the vicinity in the previous discussion are moving toward the Lesser Antilles. The eastern of the two waves is suppressed by a pocket of sinking dry air associated with the western convergence of the upper vortex...and suppressed by westerly shear on the south side of the upper vortex. The western of the two waves is crossing the southern Lesser Antilles while escaping the oppressive effects of the upper vortex...but is now suppressed by northerly shear from the paragraph P4 upper ridge. However...this western wave will enter a less hostile environment as it moves closer to the upper ridge axis...and it remains to be seen if the wave interacts with the favorable upper outflow of the upper ridge (their is computer model support for a broad Caribbean tropical low by 144 hours...but I am not yet sure if it is associated with this wave). Meanwhile...E tropical Atlc upper ridge and scattered t-storms (supported by outflow of the upper ridge) persists in relatively higher pressures E of the upper vortex.

Updated: 10:42 AM GMT on October 19, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #135

By: NCHurricane2009, 7:45 AM GMT on October 17, 2012

...WEDNESDAY OCTOBER 17 2012...3:45 AM EDT...
Hurricane Rafael is pulling northeastward from Bermuda and should transition into a non-tropical cyclone in the next 24 hours. If transition is complete by the time of my next full discussion...it will no longer receive a special feature section on this blog. However...Rafael will be a strong non-tropical cyclone that provides impacts to the north Atlantic high seas. For now...refer to the Rafael special feature section below for details on this system.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0140Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE RAFAEL...
Rafael reached a peak intensity of 90 mph max winds...a little weaker than my intensity forecast in discussion #134...and a little stronger than my intensity forecast in discussion #134A. Rafael has weakened such that he is now at the exact intensity predicted for this time in previous discussion #134...so my intensity forecast in Figure 1 below is the same as in Figure 1 of discussion #134 except that I show a more gradual weakening rate. This is because Rafael has only weakened by 5 mph over the last several hours. Rafael is weakening from SW vertical shear and increasingly cooler waters he is tracking toward...but the weakening rate has been gradual due to supportive divergence on the east side of the paragraph P2 upper trough that will gradually transition Rafael to non-tropical. My forecast in Figure 1 is identical to the 11 PM EDT NHC forecast except that I disagree on the time to non-tropical status...which I predict to occur by 11 PM Wed while the NHC predicts this to occur 6 to 12 hours after that.

Track-wise...it initially appeared Rafeal was tracking to the right-of the previous track forecast during discussion #134...but has since returned and the previous NHC forecast track has done very well in the last 24 hours. As such...the NHC has essentially made no adjustments to the track forecast...and I continue to agree with it. Rafael is turning more eastward in his northward track as he has entered the westerlies on the south side of the 984 mb cyclone in paragraph P2. The GFS model shows Rafael maintaining the same relationship with the cyclone through the forecast period shown in Figure 1...so on the surface it would seem necessary to extrapolate the current NE track rather than bend it more eastward like the NHC shows. However...I believe the NHC's eastward bend will verify because Rafael will soon pass to the north of the 1028 mb ridge center in paragraph P3. In fact with Rafael being directly south of the aforementioned cyclone...he should be tracking straight east rather than NE...but the only reason their is still a northerly component to the track is from the 1028 mb ridge to the east. Once Rafael gets north of that ridge center...he will be able to turn more eastward on the south side of the cyclone.


Figure 1: My forecast generated for Hurricane Rafael at 1 AM EDT

Impact swath in Figure 1 is based on the 11 PM tropical storm wind radius...and extrapolating that along the forecast track.

...MID-LATITUDES DISCUSSION...
P1...Next surface frontal system in the mid-latitude westerlies is entering the upper-left corner of the above atmo chart from western Canada and western US with a pair of upper troughs. The first upper trough has yet to enter the atmo chart..while the second is moving into central Canada and the central US. Upper ridge across Gulf of Mexico and western US in the previous discussion has de-amplified as the upper troughs push in...with what is left of this upper ridge over SE Mexico.

P2...Upper trough and surface frontal system over the eastern US in the previous discussion is now moving into the western Atlantic while absorbing W Caribbean upper trough fragment mentioned in paragraph P3 of the previous discussion. Western convergence of the upper trough supports dry air in SE Mexico and W Caribbean...as well as a 1014 mb ridge over the eastern US. Eastern divergence of the upper trough supports frontal depression that has intensified from 994 to 984 mb in the last 24 hrs while moving across SE Canada.

P3...Surface 982 mb gale near the south tip of Greenland in the previous discussion has moved ENE and weakened to less-than-1008 mb as its associated upper trough has moved eastward such that the gale is now suppressed by the western convergence of the upper trough. This same western convergence supports 1028 mb surface ridge that has moved from the western to the central Atlantic. Meanwhile...eastern divergence of the upper trough supports a new surface low in the upper-right corner of the above atmo chart located just offshore of the British Isles of Europe.

...TROPICAL BELT DISCUSSION...
P4...Remnants of Patty have dissipated in the vicinity of the Bahamas...Cuba...and SE Mexico.

P5...Large-sized central Atlantic upper ridge remains melded with warm core upper ridge of Rafael. The upper ridge over Rafael has become sheared-off from the storm by the upper trough in paragraph P2...and the upper ridge now extends into the SE half of the Caribbean in relatively higher pressures south of the paragraph P2 upper trough.

P6...1019 mb surface ridge in the eastern Atlantic in the previous discussion has become assimilated into the 1028 mb center of paragraph P3...and therefore is no longer an independent feature.

P7...In the tropical Atlantic east of the Lesser Antilles...cut-off upper vortex persists. Pair of tropical waves in the vicinity in the previous discussion are moving toward the Lesser Antilles while suppressed by a pocket of sinking dry air associated with the western convergence of the upper vortex...and or suppressed by westerly shear on the south side of the upper vortex. Meanwhile...the t-storm cluster continues persisting W of the Cape Verde Islands while enhanced by outflow from an E tropical Atlc upper ridge that persists in relatively higher pressures E of the upper vortex.

Updated: 7:48 AM GMT on October 17, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #134A (Special Update)

By: NCHurricane2009, 11:30 AM GMT on October 16, 2012

...TUESDAY OCTOBER 16 2012...7:30 AM EDT...
Latest satellite-derived upper-level wind barbs in GOES satellite products shows that the western outflow of Rafael is reversing to upper southwesterly winds...indicating that southwesterly shear is beginning to dominate Hurricane Rafael. Therefore...Rafael is no longer expected to strengthen. Here is my updated intensity forecast for Rafael:

5 AM Tue Oct 16 2012...85 mph...initial
11 AM Tue Oct 16 2012...85 mph...6 hr
11 PM Tue Oct 16 2012...80 mph...18 hr
11 AM Wed Oct 17 2012...75 mph...30 hr
11 PM Wed Oct 17 2012...70 mph (Becoming Non-Tropical)...42 hr

Satellite imagery...as well as radar imagery from the Bermuda Weather Service (http://www.weather.bm/radarLarge.asp)...indicate that rains over the island are starting well to the north and in advance of the hurricane. These rains are occurring outside the impact swath drawn in Figure 1 of full discussion #134...driven by upper divergence associated with the incoming upper trough. Expect occasionally heavy rains to overspread Bermuda throughout the day...with the weather in Bermuda quickly improving by tonight and early tomorrow. Aforementioned impact swath was based on tropical storm wind radius as of 11 PM EDT last night...but that radius has slightly grown in the western semicircle of Rafael as of 5 AM EDT. While this seems to increase the risk to Bermuda in terms of tropical storm sustained winds...the actual storm track is a little to the right of the previous forecast track...and with wind shear increasing across Rafael...the weather and hence the wind field is likely to lose ground in the west half of the storm. Therefore as mentioned in full discussion #134...Bermuda will barely experience tropical storm sustained winds if at all.

Return to full discussion #134 for an assessment on the rest of the Atlantic tropics.

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2012 Atlantic Hurricane Season Birdseye Discussion #134

By: NCHurricane2009, 4:30 AM GMT on October 16, 2012

...TUESDAY OCTOBER 16 2012...12:30 AM EDT...
Tropical Storm Rafael of 70 mph max winds explosively intensified into a strong category 1 hurricane of 85 mph max winds as of 8 PM EDT. The center of the hurricane is expected to pass east of Bermuda in the next 24 hours...so only tropical storm conditions is the worst case scenario for Bermuda. A tropical storm warning is currently in effect for Bermuda. See Rafael special feature section below for additional details.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1923Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE RAFAEL...
Since special update #133A...the surface center of Rafael made an early northward turn while regenerating into its heavy t-storm activity...and moreover this heavy t-storm activity has become symmetric and impressive around the surface center in the last 24 hours. The latent heat release from the unexpected amount of t-storms has inflated the warm core upper ridge over the storm such that the wind shear from the incoming paragraph P2 upper trough has been warded off. Originally the shear was expected to increase by 11 AM yesterday morning...but now we can expect the shear to increase by 11 AM tomorrow morning. However...their are signs that the shear has wanted to encroach into the storm in since 11 AM yesterday...because despite Rafael's impressiveness...he has struggled to become a hurricane until 8 PM. It is hard to say whether the incoming shear will prevent Rafael from additional strengthening..or whether the latent heat release of the t-storms and associated warm core upper ridge will continue to ward off the shear and allow more strengthening. I am fairly impressed with Rafael's uncolorized (black and white) infrared satellite appearance to the degree I think a rapid intensification episode is possible...so I forecast a peak strength 12 hours from now (by 11 AM Tue) that is a little higher than the NHC's forecast. After that...I show steady weakening as the shear and increasingly cooler waters should affect Rafael...but I flatten the weakening rate at the end of the forecast as the eastern upper divergence of the paragraph P2 upper trough should support Rafael as he transitions to non-tropical over cool waters. I have delayed the non-tropical transition time by 12 hours from the previous due to the unexpectedly high initial strength the storm currently exhibits.

Track-wise...because of Rafael's earlier than expected northward turn during special update #133A...all forecasts have adjusted to the right-of-previous...which has reduced the threat to Bermuda and eliminated the threat to Newfoundland. I agree with the current NHC track forecast shown in Figure 1...which in the short-term very consistent with the most recent NNE angle of the recorded storm track...and in the long-term gradually bends to the right consistent with when the GFS model passes the paragraph P2 994 mb cyclone to the north of Rafael such that Rafael bends in the more westerly flow on the south side of the cyclone.


Figure 1: My forecast generated for Hurricane Rafael at midnight

Impact swath in Figure 1 is based on the 11 PM tropical storm wind radius...and extrapolating that along the forecast track. The swath barely clips Bermuda for the next 24 hrs. If my impact swath forecast verifies exactly..this would mean Bermuda would barely experience significant weather from Rafael if at all. However...Bermuda is under a tropical storm warning...which should have been acted upon in case the storm bends more leftward in track for some reason.

...MID-LATITUDES DISCUSSION...
P1...Next surface frontal system in the mid-latitude westerlies is entering the upper-left corner of the above atmo chart from western Canada. Warm air advection ahead of this system supports sprawling upper ridge across the Gulf of Mexico and western US.

P2...Upper trough and surface frontal system moving across the western US in the previous discussion is now moving into the eastern US. Western convergence of the upper trough supports 1019 to 1022 mb ridge over western US extending into the W Gulf and Central America. Eastern divergence of the upper trough supports frontal depression that has intensified from 999 to 994 mb in the last 24 hrs while moving across the Great Lakes into SE Canada. Warm air advection of the 994 mb depression supports an upper ridge shifting from the eastern US into the NW Atlantic. This upper ridge is merging with large-scale upper ridge mentioned in paragraph P5.

P3...Upper trough over the W Atlantic and Caribbean has fractured into two during the last 24 hrs. One fragment is over the W Caribbean whose western convergence supports dry air in the southern Gulf of Mexico...SE Mexico...and W Caribbean. Second fragment is associated with intense surface gale near the south tip of Greenland that has weakened from 958 to 982 mb in the last 24 hrs while whirling beneath the less-divergent upper trough axis. Western convergence of this upper trough supports 1027 mb surface ridge in the W Atlantic.

...TROPICAL BELT DISCUSSION...
P4...Remnant surface trough of Patty near the central Bahamas has been shown fracturing into two in NHC TAFB maps over the last 24 hrs. One fragment is shown moving WSW toward SE Mexico while now steered by paragraph P2 1019 to 1022 mb surface ridge. Other fragment is shown to be stationary while becoming drawn toward the low pressure field of Hurricane Rafael to its east.

P5...Large-sized central Atlantic upper ridge remains melded with warm core upper ridge/outflow structure produced by the latent heat release of Hurricane Rafael's immense t-storm activity.

P6...1026 mb eastern Atlantic surface ridge in the previous discussion has weakened to 1019 mb. The dominant surface ridge over the Atlantic is becoming the 1027 mb center mentioned in paragraph P3.

P7...In the eastern tropical Atlantic...cut-off upper vortex persists. Tropical wave in the vicinity in the previous discussion is moving toward the Lesser Antilles while suppressed by a pocket of sinking dry air associated with the western convergence of the upper vortex. Meanwhile...the t-storm cluster once associated with this tropical wave persists W of the Cape Verde Islands while enhanced by outflow from a relatively new E tropical Atlc upper ridge that has developed in relatively higher pressures E of the upper vortex. A second tropical wave recently added into NHC TAFB maps appears to also be enhancing this t-storm cluster. Tropical development with this second wave will be dependent on how far west the shearing upper vortex retrogrades westward and away. Based on the lack of computer model support for this second tropical wave...it appears this wave will not develop while instead moving westward into the shearing upper vortex.

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2012 Atlantic Hurricane Season Birdseye Discussion #133A (Special Update)

By: NCHurricane2009, 4:27 AM GMT on October 15, 2012

...MONDAY OCTOBER 15 2012...12:30 AM EDT...
This special update is written concerning Tropical Storm Rafael...showing a change in direction and intensity since full discussion #133. The surface center of Rafael appears to have made an early northward turn along 65W longitude while regenerating into its heavier t-storm activity. Moreover...the the t-storm activity has become quiet strong over the center such that Rafael is almost a hurricane (75+ mph max winds). In lieu of this development...here is my updated intensity forecast for Rafael

11 PM Sun Oct 14 2012...70 mph...initial
11 AM Mon Oct 15 2012...80 mph...12 hr
11 PM Mon Oct 15 2012...80 mph...24 hr
11 AM Tue Oct 16 2012...80 mph...36 hr
11 AM Wed Oct 17 2012...75 mph (Becoming Non-Tropical)...60 hr

The updated intensity forecast uses the current rate of intensification (10 mph every 12 hours) till 11 AM Monday...when the wind shear from an upper trough (paragraph P1 of discussion #133) begins to increase. Previously I had not predicted any weakening at the end of the forecast...the philisophy being that Rafael transitions into a strong non-tropical low supported the eastern divergence of the upper trough. However...this is the first time I am suggesting an 80 mph peak intensity...and I do not expect that the shear from the upper trough and the cooler waters at the end of the forecast will allow Rafael to be stronger than 75 mph...so I weaken him from 80 to 75 mph by 11 AM Wed (when I expect him to transition to non-tropical).

The earlier than expect northward turn...occuring along 65W longitude...means Rafael will be to the right of my and the NHC's track forecasts shown in Figure 1 of discussion #133...with larger errors occuring with my forecast track that had a leftward bias with respect to NHC's. This also means the threat to Bermuda on Tuesday and threat to eastern Newfoundland (as a non-tropical low) by Thursday is reducing. However...residents in Bermuda remain under a tropical storm watch...and should be acting upon that watch until further notice.

Return to full discussion #133 for an assessment on the rest of the Atlantic tropics.

Updated: 5:34 AM GMT on October 15, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #133

By: NCHurricane2009, 9:33 PM GMT on October 14, 2012

...SUNDAY OCTOBER 14 2012...5:33 PM EDT...
Tropical Storm Rafael is pulling out of the eastern Caribbean region...and is headed toward Bermuda where a tropical storm watch has been raised. See Rafael special feature section below for details.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM RAFAEL...
Track-wise...Rafael is centered further NE than what was expected 24 hrs ago...so my and the NHC's track forecasts in Figure 1 are basically the same except that the forecast points are shifted NE from the previous. Visible satellite loops this afternoon indicate that Rafael is moving more westerly in response to the 1026 to 1030 mb ridge in paragraph P2. I continue to have a leftward bias relative to NHC's track forecasts (and even the 12Z GFS model from this afternoon) as I still think these solutions are underplaying the amount of westward steering influence the aforementioned ridge is having on Rafael. I agree with a rapid northward and NNE acceleration toward the end of the forecast as Rafael gets caught in the southwesterly flow ahead of the paragraph P1 weather system.


Figure 1: My forecast generated for Tropical Storm Rafael as of 4 PM EDT this afternoon

Intensity-wise...since inception...Rafael's east half has been under a favorable upper ridge that has been pumped-up by the system's immense t-storm latent heat release...while the west half has been suppressed by upper troughing mentioned in paragraph P2. Although this upper trough is backing off and fracturing as previously expected...Rafael has struggled to strengthen beyond 60 mph max winds. Even though Rafael briefly had a banding-type eye at 1300Z...this structure has collapsed under the shear of the upper troughing...so I only forecast slight additional strengthening in Figure 1 before the shear increases further as the paragraph P1 upper trough moves in. This means I no longer forecast Rafael to become a hurricane (75+ mph max winds)...while the NHC continues to insist that Rafael will become a hurricane. I do not show weakening toward the end of the forecast. My philosophy is that Rafael will maintain strength while supported by the eastern divergence of the paragraph P1 upper trough that ultimately makes him transition into a non-tropical system.

Impact swath in Figure 1 is based on the 11 AM tropical storm wind radius...and extrapolating that along my forecast track. This swath...which has a rightward bias with respect to the storm track...I think well-represents the sheared structure that Rafael will have throughout the forecast period. It should be noted that 24 hrs ago...we were anticipating possible direct impacts (gusty winds and rains) to reach the Virgin Islands and Puerto Rico by now. Because Rafael is further NE than expected...such direct impacts are no longer expected in these areas. Bermuda is still likely to be impacted on Tuesday (where a tropical storm watch is in effect)...and perhaps eastern Newfoundland by Thursday. If a Newfoundland scenario plays out...it is likely that Rafael will be a vigorous non-tropical cyclone by then rather than a tropical cyclone.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and surface frontal system in the mid-latitude westerlies is crossing the western US. Western convergence of the upper trough supports 1028 mb ridge over the 4-corners states...and eastern divergence of the upper trough supports 999 mb frontal depression at the Missouri-Iowa border moving ENE into northern Illinois and toward Great Lakes region. Warm air advection of the 999 mb depression supports an upper ridge shifting from the central to the eastern US..with directional vertical shear between the upper westerlies across the upper ridge and low-level southerlies ahead of the 999 mb depression. The directional shear and instability from daytime heating of land may trigger bouts of severe weather across the eastern US today and Monday. Visit www.nws.noaa.gov for latest severe weather watches and warnings with this system.

P2...Upper trough over the W Atlantic and Caribbean is fracturing into two due to strength of paragraph P1 upper ridge moving into the eastern US. Dominant surface gale of this system has bombed-out from 999 to 958 mb in the last 24 hrs while moving from NE of Newfoundland to the southern tip of Greenland. This intense gale is producing significant winds and waves over the Atlantic high seas and a large part of Greenland. Western convergence of this upper trough supports dry air in the W Atlantic...Gulf of Mexico...W Caribbean...and strong 1026 to 1030 mb ridge shifting from the NE US into the W Atlantic. Less-than-996 mb surface depression and its shortwave upper trough heading toward Europe in the previous discussion has made it to Europe and is exiting the picture from the top-right of the above atmo chart.

...TROPICAL BELT DISCUSSION...
P3...Remnant surface trough of Patty has moved WSW into the central Bahamas while steered by Rafael and 1026 to 1030 mb ridge in paragraph P2. SW vertical shear from paragraph P2 upper troughing and paragraph P2 dry air should prevent Patty from regenerating into a tropical cyclone.

P4...Central Atlantic upper ridge has melded with warm core upper ridge over Tropical Storm Rafael.

P5...1027 mb central Atlantic surface ridge in paragraph P5 of previous discussion #132 has shifted into the eastern Atlantic and is currently 1026 mb while now supported by upper convergence between southerlies from paragraph P6 E tropical Atlc upper ridge and northerlies from paragraph P4 central Atlnatic upper ridge.

P6...In the eastern tropical Atlantic...cut-off upper vortex from paragraph P3 of previous discussion #132...and tropical wave from paragraph P6 of previous discussion #132...is creating some active weather. The upper vortex has sheared-off the t-storm cluster from the tropical wave...where it persists W of the Cape Verde Islands while enhanced by outflow from a new E tropical Atlc upper ridge that has developed in relatively higher pressures E of the upper vortex. It appears the upper vortex is cold enough to de-stablize things over the warm waters such that t-storm flare ups have developed near the core of the upper vortex over the last day. Their is also a pair of new surface troughs...one west of the tropical wave...the other NNW of the tropical wave. I surmise that both surface troughs have developed due to split flow upper divergence between the flow around the upper vortex and the flow around the paragraph P4 upper ridge.

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2012 Atlantic Hurricane Season Birdseye Discussion #132

By: NCHurricane2009, 11:42 PM GMT on October 13, 2012

...SATURDAY OCTOBER 13 2012...7:45 PM EDT...
In the last 36 hours...Patty has dissipated as a tropical cyclone just north of the eastern Bahamas. See paragraph P4 for statement on the remnant of Patty.

Strong tropical wave Invest 98-L has strengthened into Tropical Storm Rafael during the last 36 hours while moving northwest and northward across the eastern Caribbean region. The northern Lesser Antilles are currently affected...while Puerto Rico and the Virgin Islands are likely to be affected in the next 24 hours. Bermuda will likely be affected by Rafael on Tuesday. See Rafael special feature section below for details.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1331Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM RAFAEL...
Rafael is a dynamic situation...first developing into a tropical storm in the last 36 hrs from a strong tropical wave while tracking NW across the eastern Caribbean region...and then turning north and NNE while the center regenerates under the heavy t-storms in its eastern semicircle. All the while...Rafael is quickly becoming better organized and strengthening. This discussion on this currently dynamic situation will refer to the 11 AM EDT NHC forecast (shown in Figure 1)...my 3 PM EDT forecast (also shown in Figure 1)...and the 5 PM EDT NHC forecast (not shown in Figure 1). It should be noted that the 11 AM and 5 PM EDT NHC track forecasts are quiet similar...except that the NHC has adjusted their short-term track forecast rightward to account for the reformation of the center into the heavy t-storm activity.

Track-wise...when I made my 3 PM EDT forecast shown in Figure 1...I had Rafael's center moving into the waters midway between the Lesser Antilles and Virgin Islands for late this evening as I suspected Rafael's center was regenerating into his t-storms...which made my initial track forecast have a rightward bias relative to the 11 AM NHC's. Indeed this is proving to the be the case...and the 5 PM NHC forecast has adjusted toward this solution. For the longer-term...I develop a leftward bias relative to NHC's 11 AM and 5 PM track forecasts (and even the 12Z GFS model from this afternoon) as I think these solutions underplay the amount of westward steering influence the strong 1034 mb NE US ridge (paragraph P2) is going to have as it passes north of Rafael. I agree with a rapid northward and NNE acceleration toward the end of the forecast as Rafael gets caught in the southwesterly flow ahead of the paragraph P1 weather system.


Figure 1: The 11 AM EDT NHC forecast (black line) and my 3 PM EDT forecast (red line) for Tropical Storm Rafael. I had to upgrade my intensity forecast just after 5 PM due to the strengthening that Rafael showed at 5 PM.

Intensity-wise...since inception...Rafael's east half has been under a favorable upper ridge that has been pumped-up by the system's immense t-storm latent heat release...while the west half has been suppressed by an upper trough mentioned previously in paragraph P3 of discussion #131...and now suppressed by paragraph P2 upper troughing. Because the surface center of the storm is regenerating NNE into its heavy t-storm activity...he is now strengthening a little faster than anticipated. For example in Figure 1...you can see the intensity forecast I came up with before the 5 PM update...and my newly-upped intensity forecast I came up with after the 5 PM upgrade to Rafael's strength. My upgraded intensity forecast is similar to the NHC...but my forecast strengthens Rafael into a hurricane (75+ mph) a little sooner than NHC's 5 PM forecast. This episode of strengthening is supported by the fact that models show the paragraph P2 upper troughing backing off while the favorable upper ridge/outflow over the storm grows and becomes more symmetrical. The NHC forecasts Rafael will peak at 80 mph...but I choose 75 as my left-leaning longer-term forecast track places Rafael closer to incoming southwesterly shear delivered by paragraph P1 upper trough. I also choose to keep Rafael elevated at hurricane strength late in the forecast while the NHC chooses to weaken him below hurricane force by then. My philosophy is that Rafael will maintain strength while supported by the eastern divergence of the paragraph P1 upper trough that ultimately makes him transition into a non-tropical system.

Impact swath in Figure 1 is based on the coldest-cloud tops seen in the eastern semicircle of Rafael's infrared satellite display. This swath is a larger than the tropical storm wind radius...to also account for heavy rains that Rafael's t-storm activity could deliver. Swath is extrapolated along my forecast track...and note that the swath has a rightward bias with respect to track throughout as I don't believe Rafael will ever be a perfectly symmetrical storm from current shearing of paragraph P2 upper troughing and future shearing from paragraph P1 upper trough not long after. Rafael's significant weather (particularly the heavy rains) has been slamming the Lesser Antilles for several hours...but has not yet arrived to Puerto Rico or the Virgin Islands. My more-left track forecast moreso allows the weather biased to the east side of Rafael to transfer into these currently calm areas in the next 24 hours...while the NHC forecast track would allow for the weather in Puerto Rico and Virgin Islands to be less severe. Later-on...Bermuda has a high risk of impact on Tuesday...and perhaps Newfoundland could be affected by Thursday depending on the exact track the storm takes. However...Rafael is more likely to affect Newfoundland as a vigorous non-tropical low rather than a tropical cyclone.

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and surface frontal system in the mid-latitude westerlies has entered the upper-left of the above atmo chart from the western US. Western convergence of the upper trough supports 1021 mb ridge over the 4-corners states...and eastern divergence of the upper trough supports 1002 mb frontal depression over South Dakota. Warm air advection of the 1002 mb depression has amplified an upper ridge over the central US..with directional vertical shear between the upper westerlies across the upper ridge and low-level southerlies ahead of the 1002 mb depression. The directional shear and instability from daytime heating of land has triggered severe weather and tornadoes across the central US. Visit www.nws.noaa.gov for latest central US severe weather watches and warnings with this system.

P2...Upper troughing over North America is finally shifting eastward into the W Atlantic while pushed by paragraph P1 central US upper ridge. Due to the amplitude of the central US upper ridge...the upper troughing has amplified southward into much of the Caribbean and is absorbing the central Atlantic to eastern Caribbean upper vortices mentioned in paragraph P3 of previous discussion #131. 968 mb surface gale on the east coast of Canada...once supported by the eastern divergence of the upper troughing...has weakened to 975 mb in the last 36 hrs while nearly stationary and becoming exposed to the less-divergent upper trough axis passing overhead. 1010 mb frontal depression shifting into SE Canada 36 hrs ago has intensified with the eastern divergence of the upper troughing and is now 999 mb just NE of Newfoundland. Western convergence of this upper troughing supports dry air in the W Atlantic...Gulf of Mexico...W Caribbean...and strong 1034 mb surface ridge that has shifted from the central to the NE US. 990 mb surface depression and its shortwave upper trough E of Greenland 36 hrs ago has exited the picture while moving into Europe...and yet another surface depression (less-than-996 mb) and its shortwave upper trough is heading toward Europe. This depression spun up along the occluded front of aforementioned 975 mb gale over the E coast of Canada...and the attendant shortwave upper trough is fracturing into two thanks to the strength of the central Atlantic upper ridge mentioned in paragraph P5.

P3...Upper vortex south of the Azores is retrograding SW around the central Atlantic upper ridge mentioned in paragraph P5. Convergence on the NW quad of this upper vortex supports 1027 mb central Atlantic surface ridge.

...TROPICAL BELT DISCUSSION...
P4...Due to SW vertical shear from paragraph P2 upper troughing...Patty has dissipated as a tropical cyclone in the last 36 hours. Visible satellite this afternoon shows a series of surface swirls accelerating southwestward toward the central Bahamas while steered by strong NE US surface ridge discussed in paragraph P2. The multiplicity of swirls indicates that Patty is now a surface trough as opposed to a singular surface low. Expect dry air in paragraph P2 and the continued shear to prevent Patty from regenerating into a tropical cyclone.

P5...W Atlantic upper ridge has shifted into the central Atlantic in advance of paragraph P2 upper troughing.

P6...In the last 36 hours...a tropical wave has recently emerged from western Africa...and was placed just west of the Cape Verde Islands in TAFB maps this afternoon. Although its t-storm actvity is enhanced by divergence on the SE half of the paragraph P3 upper vortex...it is in unfavorable SW vertical shear induced by the same upper vortex.

Updated: 11:49 PM GMT on October 13, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #131A (Special Update)

By: NCHurricane2009, 11:35 AM GMT on October 12, 2012

...FRIDAY OCTOBER 12 2012...7:35 AM EDT...
While I was writing full discussion #131...new data as of the 5 AM EDT NHC forecast shows Patty located further south than previously thought...and has begun drifting SSW. Therefore...the NHC has adjuster their track forecast further south between 11 PM EDT and 5 AM EDT. Therefore my track forecast in Figure 1 of discussion #131...which has a slight north bias relative to the 11 PM EDT forecast...is no longer valid. With the center further south and her track SSW...her center is further removed from her t-storm activity...and therefore satellite classification techniques suggest she has weakened to a minimal tropical storm of 40 mph max winds. If current trends continue...she could easily weaken to a tropical depression later today and dissipate a lot sooner than previously forecast in discussion #131.

These changes in Patty do not increase the threat to the Bahamas or any other land areas beyond which her forecast WSW track will take her. As explained in discussion #131...Patty is not expected to bring tropical storm winds or heavy rains to any land areas.

Return to full discussion #131 for an update on the rest of the Atlantic tropics...in particular special feature Invest 98-L which could quickly spin up into a tropical cyclone while moving into land areas in the eastern Caribbean. Visit www.nhc.noaa.gov for up to the minute information on 98-L...in particular should tropical cyclone formation occur and any tropical storm warnings be issued in the next 24 hrs before my next full blog update. My next full blog update should occur sometime Saturday morning or early Saturday afternoon.

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2012 Atlantic Hurricane Season Birdseye Discussion #131

By: NCHurricane2009, 10:55 AM GMT on October 12, 2012

...FRIDAY OCTOBER 12 2012...6:55 AM EDT...
In the last 24 hours...tropical disturbance Invest 97-L just north of the eastern Bahamas has strengthened into tropical depression sixteen then into Tropical Storm Patty. Patty will be accelerating west-southwestward across the Bahamas and Cuba by late this weekend and Monday. However...it is expected to be a remnant surface trough by then. See Patty special feature section below for details.

Attention continues turning to tropical wave Invest 98-L en route to the Lesser Antilles. It is becoming more apparent that tropical cyclone formation will be likely with this system...and therefore I have upgraded it to a special feature on this blog. This system could soon spin up into a tropical cyclone that brings tropical storm conditions to the Lesser Antilles...Virgin Islands...and Puerto Rico. In addition...computer model runs suggest that Bermuda should also monitor the progress of this system. See the Invest 98-L special feature section below for details.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0123Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM PATTY...
Under the upper outflow and reduced shear of the SW end of the paragraph P4 upper ridge...tropical low Invest 97-L has strengthened to Tropical Storm Patty in the last day. However...as anticipated in my previous remarks on this system...1010 mb frontal depression in paragraph P1 is re-amplifying the upper troughing such that the favorable W Atlantic upper ridge is getting booted out and unfavorable westerly vertical shear is pushing in. However...with the 00Z GFS model showing the east half of Patty under the favorable upper ridge for another 24 hrs...I agree with the NHC 11 PM EDT intensity forecast...which keeps Patty at current strength for 24 more hours. I also agree with the 11 PM EDT NHC advisory weakening rate (albeit I forecast the final advisory will be 11 PM Sat while the NHC said by 11 PM Sunday)...which shows weakening beginning in 36 hrs. This is consistent with the 36-hour and beyond 00Z GFS upper wind forecast showing the favorable upper ridge being pushed out altogether while becoming replaced by a large area of shearing southwest upper winds from the paragraph P1 upper troughing.


Figure 1: My forecast for Tropical Storm Patty generated very early this morning

As I anticipated in my previous discussion of this system...Patty is stationary while trapped between the paragraph P1 central US surface ridge and paragraph P2 Atlantic surface ridge. With the two ridges shown in models to be of equal strength and opposing influence...coupled with the fact that the gap between the two ridges will be re-enforced by the 968 mb and 1010 mb depressions in paragraph P1...I still expect Patty to be stationary for the timeframe that is the next 24 hrs as I stated yesterday. Alternatively...the NHC shows a southward drift for Patty in the next 24 hrs (so I have a north bias relative to NHC from the get-go as seen in Figure 1)...while the 00Z GFS shows a northeast drift in the next 24 hrs. Therefore I believe my stalled forecast track for the next 24 hrs is a good compromise between these two solutions. After 24 hrs...the models agree that the central US ridge in paragraph P1 will eject eastward and pass to the north of Patty...and tropical wave Invest 98-L should be pushing in from the east by that time. Therefore...I agree with the NHC on an accelerating WSW track after 24 hrs while steered by 98-L and the ridge (but my track line is a little north of the NHC's becauase of my aformentioned initial north bias for the first 24 hrs).

Blue-dashed impact swath in Figure 1 is based on the 11 PM EDT NHC tropical storm wind radius...and extrapolating that along my forecast track along the length where I forecast Patty to be a tropical storm. With that said...we can expect Patty to not bring tropical storm conditions to the Bahamas or any land areas beyond in her forecast WSW track...because she should be dissipated from vertical shear by then. It is hard to distinguish Patty's cold cloud-tops from that of the paragraph P1 W Atlantic cold front's...but it is likely their is a large area of offshore heavy rain east of the center of Patty both inside and outside my impact swath. Because it is hard to distinguish the potential rain shield of Patty from the front's...that is why my impact swath simply represents the area of expected tropical storm winds rather than the area of heaviest rain. I expect the front to sweep up all of Patty's eastern t-storm activity by the time she accelerates WSW...so this area of heavy rain should not affect the Bahamas or any other land areas her WSW track will bring her.

...SPECIAL FEATURE...STRONG TROPICAL WAVE INVEST 98-L...
Tropical wave Invest 98-L with 1006 mb low pressure spin is currently approaching the Lesser Antilles..and has gotten better organized in the last 24 hours. It continues to be enhanced by upper outflow of paragraph P3 eastern tropical Atlantic upper ridge...which has become amplified over the system thanks to the system's t-storm latent heat release and thanks to the anticipated diminishing of SW-NE upper trough in paragraph P3. However...the surface low pressure center of 98-L is on the west edge of the favorable upper ridge...so the system still is fighting some SW vertical shear from the SW-NE upper trough for the time being. With the 00Z GFS showing the favorable upper ridge continuing to expand and following the system for the next days...coupled with continued diminishing of the SW-NE upper trough...98-L could quickly spin up into a tropical storm in the next 24 hours...and in fact could become a strong tropical cyclone (certainly stronger than current Tropical Storm Patty).

Models support 98-L tracking NW across the eastern Caribbean region (Lesser Antilles...Virgin Islands...and Puerto Rico area) while rounding the SW edge of paragraph P2 central Atlantic surface ridge...the NW track also supported by expanding ridge weakness from Patty...as well as the 968 mb and 1010 mb frontal depressions mentioned in paragraph P1. The central US surface ridge in paragraph P1 is then progged to eject eastward to the north of 98-L...supporting a more west track toward the Bahamas...but the models show the next mid-latitude system quickly kicking in behind that ridge so that 98-L misses the Bahamas and turns northward toward Bermuda. It is important to emphasize that weak to moderate tropical storm conditions could quickly spin up over portions of the Lesser Antilles...Virgin Islands...and Puerto Rico area in the next 24 to 48 hrs...and that Bermuda could be affected by this system before the next 120 hrs (5 days) passes.

...MID-LATITUDES DISCUSSION...
P1...Upper troughing over North America is being re-enforced by cool air advection from strong surface frontal cyclone that has intensified from 985 to 968 mb while moving from eastern Hudson Bay to the E coast of Canada. Cool air advecdtion of 1010 mb frontal depression that shifted from Montana to SE Canada is also supporting the upper troughing. Western convergence of this upper troughing is supporting 1024 and 1029 mb surface ridge centers over the central US. Intense 969 mb frontal cyclone just east of Greenland has weakened to 990 mb while whirling beneath the less-divergent axis of its shortwave upper trough. A long frontal zone formerly extended from this 990 mb center...reaching as far SW as the W Atlantic. This front is now controlled by the aformentioned 968 mb center over the E coast of Canada.

P2...Upper vortex continues south of the Azores. Western convergence of this upper vortex is supporting 1027 mb central Atlantic surface ridge.

...TROPICAL BELT DISCUSSION...
P3...SW-NE tilted upper trough in the central Atlantic and eastern Caribbean persists...currently established as a pair of upper vortices. In relatively higher pressures west of the upper trough...a western Caribbean upper ridge persists. Yet another upper ridge persists in relatively higher pressures east of this upper trough...located in the eastern tropical Atlantic over special feature Invest 98-L. To the east of that...the upper trough W of the Cape Verde Islands in the previous discussion has become absorbed by the paragraph P2 upper vortex.

P4...W Atlantic upper ridge remains amplified across the north Atlantic due to warm air advection ahead of 990 mb and 968 mb gale centers mentioned in paragraph P1.

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2012 Atlantic Hurricane Season Birdseye Discussion #130

By: NCHurricane2009, 4:32 AM GMT on October 11, 2012

...OCTOBER 11 2012...12:35 AM EDT...
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

As stated in special update #129A...tropical disturbance Invest 97-L just north of the eastern Bahamas has re-organized to the degree it could become a tropical cyclone in the short-term. See special feature section below for additional details.

Attention continues turning to tropical wave Invest 98-L en route to the Lesser Antilles. Computer models suggest tropical cyclone formation potential as the wave moves into the eastern Caribbean area by 48 to 96 hours...but the tropical wave must first survive a current onslaught of westerly vertical shear. In addition to the eastern Caribbean...early computer model runs suggest that Bermuda should also monitor the progress of this system. See paragraph P5 for additional details on this feature.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DISTURBANCE INVEST 97-L...
After beginning to accelerate NE with the surface front of the 969 mb gale in paragraph P1 24 hrs ago...tropical low 97-L (now 1013 mb) is drifting SE at a location just north of the eastern Bahamas while becoming trapped between the central US ridge in paragraph P1 and central Atlantic ridge in paragraph P2. With the two ridges shown in models to be of equal strength and opposing influence...coupled with the fact that the gap between the two ridges will be re-enforced by the 985 mb and 1010 mb depressions in paragraph P1...expect 97-L to be generally stationary at its current location for the next 48 hours. Invest 97-L has become well-organized while taking advantage of upper outflow and reduced shear under the paragraph P4 W Atlantic upper ridge...so the best window of opportunity for tropical cyclone formation is in the next 24 hrs while this condition persists. After 24 hrs...the aforementioned 1010 mb frontal depression will re-amplify the paragraph P1 upper troughing such that the favorable W Atlantic upper ridge gets booted out and unfavorable westerly vertical shear pushes in.

After 48 hrs...the models agree that the central US ridge in paragraph P1 will eject eastward and pass to the north of 97-L...and tropical wave Invest 98-L (paragraph P5) should be pushing in from the east by that time. Between 48 and 120 hrs...CMC and NOGAPS show 97-L tracking WSW across the Bahamas...Cuba...and into the W Caribbean while steered by the ridge and 98-L. A check with this evening's 18Z GFS shows 97-L remaining under hostile westerly vertical shear if such a WSW track occurred...so if the CMC and NOGAPS verify...we will likely be tracking a remnant surface trough by then rather than a tropical cyclone.

...MID-LATITUDES DISCUSSION...
P1...Upper troughing over North America is being re-enforced by cool air advection from strong surface frontal cyclone that has intensified from 994 to 985 mb while nearly stationary over eastern Hudson Bay in the last 24 hrs. A developing 1010 mb frontal depression from Montana will soon dive eastward across the northern US and also re-enforce this upper trough. Western convergence of this upper troughing is supporting a central US surface ridge (currently 1026 mb). Intense 977 mb frontal cyclone just east of Greenland in the previous discussion has intensified further to 969 mb with the eastern divergence of its shortwave upper trough (meanwhile the western convergence of this same upper trough supports 1024 mb ridge moving offshore from SE Canada). A long frontal zone extends from the 969 mb center...reaching as far SW as the W Atlantic where a new 1009 mb depression has formed offshore of the NE US with the support of eastern divergence from the above-mentioned North America upper troughing.

P2...Surface and upper-level trough in the NE Atlantic continues. The surface trough is becoming absorbed into the 969 mb gale east of Greenland mentioned in paragraph P1. The upper trough has amplified into an upper vortex south of the Azores thanks to equal amplification of W Atlantic upper ridge into the north Atlantic as discussed in paragraph P4. Western convergence of this upper vortex is supporting 1026 mb central Atlantic surface ridge.

...TROPICAL BELT DISCUSSION...
P3...SW-NE tilted upper trough in the central Atlantic and eastern Caribbean persists...currently linked with upper vortex south of the Azores in paragraph P2. In relatively higher pressures west of the upper trough...a western Caribbean upper ridge persists whose upper outflow supports scattered t-storm clouds across Central America and adjacent Caribbean waters. Yet another upper ridge persists in relatively higher pressures east of this upper trough...located in the eastern tropical Atlantic. This eastern tropical Atlantic upper ridge remains de-amplified by the aforementioned central tropical Atlantic upper trough...and by upper trough W of the Cape Verde Islands. Even though I have no satellite-derived 200 mb (upper wind) barbs in this area from the GOES-E satellite outage...I am using the adjacent wind barbs and the curvature of the cloud band SE of the Cape Verde Islands to deduce the aforementioned upper trough W of the Cape Verde Islands. I surmise the cloud band SE of the Cape Verde Islands is supported by the eastern divergence of this upper trough.

P4...W Atlantic upper ridge has amplified into the north Atlantic due to warm air advection ahead of 969 mb and 985 mb gale centers mentioned in paragraph P1. SW end of this upper ridge supports upper outflow of tropical disturbance Invest 97-L north of the eastern Bahamas (see above special feature section for additional details on 97-L).

P5...Tropical wave Invest 98-L with 1008 mb low pressure spin is currently approaching the Lesser Antilles..and has not gotten any better organized in the last 96 hours. It continues to be enhanced by upper outflow of paragraph P3 eastern tropical Atlantic upper ridge. As described in that paragraph...the upper ridge has de-amplified such that zonal shearing upper westerlies have increased across the tropical wave. The CMC...Euro (ECMWF)...GFS...and NOGAPS models insist on tropical cyclone formation from this system as it enters the eastern Caribbean region in the 48 to 96 hr timeframe. A study of this evening's 18Z GFS shows that the SW-NE upper trough in paragraph P3 should be diminishing during that timeframe...allowing the upper ridge over the tropical wave to expand and support such development. First waiting to see how well the tropical wave survives the current and unfavorable westerly vertical shear. If the tropical wave turns out to be in good shape as we approach the 48 hr timeframe...then I will be upgrading it to a special feature on this blog. Models support 98-L tracking NW across the eastern Caribbean region while rounding the SW edge of paragraph P2 central Atlantic surface ridge...the NW track also supported by expanding ridge weakness from 985 mb and 1010 mb depressions mentioned in paragraph P1. The central US surface ridge in paragraph P1 is then progged to eject eastward to the north of 98-L...supporting a more west track toward the Bahamas...but the models show the next mid-latitude system quickly kicking in behind that ridge so that 98-L misses the Bahamas and turns northward toward Bermuda.

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2012 Atlantic Hurricane Season Birdseye Discussion #129A (Special Update)

By: NCHurricane2009, 8:04 PM GMT on October 10, 2012

...OCTOBER 10 2012...4:10 PM EDT...
Disturbed weather just north of the eastern Bahamas...associated with surface disturbance Invest 97-L and western Atlantic surface cold front...has become well-organized underneath the favorable outflow of a western Atlantic upper ridge. This area of weather was mentioned in paragraph P4 of full discussion #129. After being removed from the NHC tropical weather outlook early this morning...this area of weather has been re-introduced into the outlook with a 10% chance of tropical cyclone formation in the next 48 hours. Given the well-organized satellite appearance and favorable upper winds...I suspect tropical cyclone formation is much more likely...and therefore will be introducing this as a special feature in my next full blog update.

In the meantime...return to full discussion #129 for info on the rest of the Atlantic tropics.

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2012 Atlantic Hurricane Season Birdseye Discussion #129

By: NCHurricane2009, 10:13 AM GMT on October 10, 2012

...OCTOBER 10 2012...6:20 AM EDT...
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

See paragraph P4 for statement on disturbance Invest 97-L pulling northeastward from the Bahamas.

Attention continues turning to tropical wave Invest 98-L en route to the Lesser Antilles. Computer models suggest tropical cyclone formation potential as the wave moves into the eastern Caribbean area by 72 to 120 hours...but the tropical wave must first survive a current onslaught of westerly vertical shear. See paragraph P5 for additional details on this feature.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0724Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper troughing over North America is being re-enforced by cool air advection from strong surface frontal cyclone that has intensified from 998 to 994 mb while moving from NE North Dakota to southern Hudson Bay in the last 24 hours. Western convergence of this upper troughing is supporting a new central US surface ridge (currently 1025 mb). 1009 mb frontal depression moving NE across Newfoundland in the previous discussion has rapidly intensified to 977 mb with the support of eastern divergence from its shortwave upper trough. This intense depression clipped the southern tip of Greenland in the last 24 hours...and is now just east of Greenland. Previous central US surface ridge (currently 1027 to 1020 mb) has shifted eastward into SE Canada and the eastern US while becoming associated with the western upper convergence of 977 mb gale's shortwave upper trough.

P2...What is left of NE Atlantic deep-layered cyclone is a surface and upper-level trough over and just NE of the Azores. The upper trough has gained SW-NE tilt while becoming squeezed by amplifying W Atlantic upper ridge in paragraph P4. Western convergence of this upper trough is supporting a 1028 mb surface ridge that has shifted from the W to central Atlantic.

...TROPICAL BELT DISCUSSION...
P3...Central tropical Atlantic upper vortex...still extending into the eastern Caribbean...is now a SW-NE tilted upper trough now linked with SW-NE upper trough in paragraph P2. In relatively higher pressures west of the upper trough...a western Caribbean upper ridge persists whose upper outflow earlier triggered an impressive t-storm cluster over Nicaragua...Honduras...and adjacent Caribbean waters. Yet another upper ridge persists in relatively higher pressures east of this upper trough...located in the eastern tropical Atlantic. This eastern tropical Atlantic upper ridge is de-amplified by the aforementioned central tropical Atlantic upper trough...and by upper vortex W of the Cape Verde Islands that appears to have de-amplified into an upper trough. Even though I have no satellite-derived 200 mb (upper wind) barbs in this area from the GOES-E satellite outage...I am using the adjacent wind barbs and the curvature of the cloud band SE of the Cape Verde Islands to deduce the aforementioned upper trough W of the Cape Verde Islands. I surmise the cloud band SE of the Cape Verde Islands is supported by the eastern divergence of this upper trough.

P4...W Atlantic upper ridge has amplified due to warm air advection ahead of 977 mb and 994 mb gale centers mentioned in paragraph P1. Surface disturbance Invest 97-L (now a 1012 mb low) is pulling NE from the Bahamas while steered by SW flow ahead of the 977 mb gale's W Atlantic cold front. Satellite imagery suggests 97-L and the surface front are gradually melding together...the band of weather associated with both overspreading Bermuda this morning. With the W Atlantic upper ridge shown to persist in computer model runs...I am watching to see if this band of weather gains any tropical organization under the outflow of the upper ridge in the next days.

P5...Tropical wave Invest 98-L with 1008 mb low pressure spin is currently approaching the Lesser Antilles..and has not gotten any better organized in the last 72 hours. It continues to be enhanced by upper outflow of paragraph P3 eastern tropical Atlantic upper ridge. As described in that paragraph...the upper ridge has de-amplified such that zonal shearing upper westerlies have increased across the tropical wave. The CMC...Euro (ECMWF)...GFS...and NOGAPS models insist on tropical cyclone formation from this system as it enters the eastern Caribbean region in the 72 to 120 hr timeframe. A study of this evening's 00Z GFS shows that the SW-NE upper trough in paragraph P3 should be diminishing during that timeframe...allowing the upper ridge over the tropical wave to expand and support such development. First waiting to see how well the tropical wave survives the current and unfavorable westerly vertical shear. If the tropical wave turns out to be in good shape as we approach the 72 hr timeframe...then I will be upgrading it to a special feature on this blog.

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2012 Atlantic Hurricane Season Birdseye Discussion #128

By: NCHurricane2009, 8:25 AM GMT on October 09, 2012

...OCTOBER 9 2012...4:30 AM EDT...
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

In the western part of the Atlantic tropical basin...continuing to watch the surface trough of Invest 97-L (paragraph P4)...a surface tropical low near Costa Rica (paragraph P6)...and the melding together of a western Atlantic upper ridge (paragraph P4) and western Caribbean upper ridge (paragraph P3). The surface trough of Invest 97-L has entered hostile westerly vertical shear associated with the paragraph P1 weather system...and therefore should not develop. The Costa Rica surface low should soon make landfall across Central America and enter the eastern Pacific. With no more tropical development potential in the western Atlantic basin expected...this is my last statement on this area in the intro section of my blogs.

In the central part of the Atlantic tropical basin...the t-storms associated with the central Atlantic upper vortex (paragraph P3) have dwindled in the last 24 hours. Tropical development here was never anticipated due to the t-storms being associated with an upper feature rather than a surface feature.

Attention is turning to the eastern part of the tropical Atlantic basin...where a tropical wave has been upgraded to Invest 98-L. Computer models suggest tropical cyclone formation potential as the wave moves into the Caribbean area by 96 to 120 hours...but the tropical wave must first survive an onslaught of westerly vertical shear expected before that timeframe. See paragraph P8 for additional details on this feature.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...984 mb surface gale and its supporting upper trough moving across Greenland are exiting the above atmo chart from the top-center. Despite the departure of this upper trough...upper troughing over North America is being re-enforced by cool air advection from yesterday's 1002 mb Canadian frontal depression (now 1006 mb over E Hudson Bay) and another Canadian frontal depression that has entered the picture...currently 998 mb over NE North Dakota. Eastern divergence of this upper troughing has supported a new frontal depression offshore of the eastern US which has rapidly zipped NE across Newfoundland at 1009 mb. This 1009 mb depression's cool air advection has carved out its own shortwave upper trough...and yesterday's strong central US surface ridge (currently 1025 to 1026 mb) is shifting eastward while becoming associated with the western convergence of this new upper shortwave trough.

P2...Deep-layered cyclone in the eastern open Atlantic is slowly shifting toward Europe. Upper-levels of this system continues to be marked by large upper trough. Western convergence of this upper trough is supporting a 1028 mb W Atlantic surface ridge. What is left of NE Atlantic surface ridge from paragraph P3 of previous discussion #127 is becoming assimilated into the W Atlantic surface ridge. Surface center of the deep-layered cyclone...supported by eastern divergence of the upper trough...is moving slowly NNE in the waters well north of the Azores.

...TROPICAL BELT DISCUSSION...
P3...Central tropical Atlantic upper vortex persists...still extending to a smaller upper vortex near Haiti and the Dominican Republic. In relatively higher pressures west of both upper vortices...a western Caribbean upper ridge has built. Yet another upper ridge persists in relatively higher pressures east of these upper vortices...located across the eastern tropical Atlantic. The east end of this eastern tropical Atlantic upper ridge is de-amplified by an upper vortex that has been dropped off by paragraph P2 upper trough (Even though I have no satellite-derived 200 mb (upper wind) barbs in this area from the GOES-E satellite outage...the upper vortex continues to be confirmed by Meteosat-9 water vapor imagery at a location W of the Cape Verde Islands).

P4...W Atlantic upper ridge persists in advance of large-scale paragraph P1 upper troughing. Disturbance Invest 97-L over the Bahamas...supported by the upper outflow of this upper ridge...has seen more impressive curved t-storm bands in the last 24 hours. However...the surface low has been downgraded to a surface trough...and the disturbance has drifted westward while steered by a merger of the central US surface ridge (paragraph P1) and W Atlantic surface ridge (paragraph P2). On this track...the disturbance is moving into hostile westerly vertical shear delivered by paragraph P1 upper troughing...and therefore I continue to not have a special feature section on this blog for 97-L.

P5...Intermittent disturbed weather across the Bay of Campeche...southern Gulf of Mexico...and Florida remains supported by eastern divergence of paragraph P1 upper troughing. Surface forcing for this area of weather is also coming from cold front extending from 1009 mb depression in paragraph P1...and coming from surface troughs in the Bay of Campeche (one of which is a northern fracture from tropical wave in paragraph P6 below).

P6...Tropical wave moving into the western Caribbean in the previous discussion has fractured into two areas. Its northern end is contributing to weather discussed in paragraph P5 above. Its southern end is a 1010 mb tropical low pressure near Costa Rica and Panama that is producing t-storms with the aid of upper outflow from paragraph P3 W Caribbean upper ridge. Although this is a very favorable upper wind configuration for tropical cyclone development...the tropical low is about to continue westward into Central America and eventually into the eastern Pacific. Perhaps it will eventually become the next eastern Pacific tropical cyclone (eastern Pacific activity is not covered on this blog).

P7...I had been tracking a suspect tropical wave...which in the previous discussion I placed in the waters between the Lesser Antilles and Cape Verde Islands. Because the associated t-storm cluster has disappeared since 1200Z October 5...and because the NHC TAFB has not added this wave to their maps....I am cancelling this wave from my analyses.

P8...Tropical wave with 1008 mb low pressure spin in the eastern Atlantic...entering the waters midway between the Cape Verde Islands and Lesser Antilles...has not gotten any better organized in the last 48 hours...but has been upgraded to tropical disturbance Invest 98-L in the last 24 hours. It continues to be enhanced by upper outflow of paragraph P3 eastern tropical Atlantic upper ridge...and so far has managed to avoid oppressive effects of nearby upper vortex that have de-amplified the east end of this upper ridge. This is because the tropical wave is well southwest of this upper vortex. Based on animation of this evening's computer models...this tropical wave has about 24 hours to develop before encountering hostile westerly vertical shear by 48 hours delivered by the pair of cut-off upper vortices mentioned in paragraph P3. Unlike previous nights...the CMC...Euro (ECMWF)...GFS...and NOGAPS models are all suggesting tropical cyclone formation from this system as it enters the Caribbean region by 96 to 120 hrs. A study of this evening's 00Z GFS shows that the shearing cut-off upper vortices should be diminishing by that time...allowing the upper ridge over the tropical wave to expand and support such development. First waiting to see how well the tropical wave survives the expected onslaught of shear. If the tropical wave turns out to be in good shape as we approach the 96 hr timeframe...then I will be upgrading it to a special feature on this blog.

Updated: 8:28 AM GMT on October 09, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #127

By: NCHurricane2009, 3:56 AM GMT on October 08, 2012

...OCTOBER 7 2012...11:55 PM EDT...
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

In the western part of the Atlantic tropical basin...continuing to watch the surface low of Invest 97-L (paragraph P5)...a surface tropical wave (paragraph P7)...and the melding together of a western Atlantic upper ridge (paragraph P5) and southern Caribbean upper ridge (paragraph P4). So far the surface low of Invest 97-L has been the only focal point of attention...but it shows no signs of tropical cyclone formation as noted in paragraph P5.

In the central part of the Atlantic tropical basin...although t-storms remain curved and organized northeast of the Lesser Antilles...this activity is associated with a long-lasting central Atlantic upper vortex rather than a surface feature (paragraph P4).

In the eastern part of the tropical Atlantic basin...a tropical wave has not gotten any better organized. See paragraph P9 below for details on its window of opportunity.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper vortex over E Canada has de-amplified into an upper trough on the east coast of Canada...with the 994 and 993 mb gale centers it supports with its eastern divergence combining into one gale center that has intensified to 984 mb heading for Greenland. Despite the departure of the upper trough onto the east coast of Canada...upper troughing over North America is being re-enforced by cool air advection from 1002 mb Canadian frontal depression and other Canadian frontal depressions soon to follow. Western convergence of the upper troughing continues supporting strong central US surface ridge (now 1028 mb) that continues driving in unseasonably cold air.

P2...Deep-layered cyclone in the eastern open Atlantic is shifting toward Europe. Upper-levels of this system continues to be marked by impressive upper trough. Western convergence of this upper trough is supporting a 1022 to 1018 mb W Atlantic surface ridge. Strong surface center of the deep-layered cyclone...supported by eastern divergence of the upper trough...is shifting NNE from the Azores.

P3...Based on Meteosat-9 animation over the last day...shortwave upper trough has moved into Europe and left the scope of the above birdseye charts. NE Atlantic surface ridge was formerly supported by western convergence of the upper trough activity in this area. Due to the GOES-E satellite outage...in the above atmo chart I do not have satellite-derived 200 mb (upper-level) wind barbs in this region. However...I speculate their is an upper ridge ahead of the paragraph P2 upper trough whose eastern convergence is now supporting this NE Atlantic surface ridge.

...TROPICAL BELT DISCUSSION...
P4...Central tropical Atlantic upper vortex persists...still extending to a smaller upper vortex near Haiti. While t-storms remain curved and organized at a location NE of the Lesser Antilles...this organization is occurring about the central Atlantic upper vortex rather than a surface feature. Upper convergence on west side of both upper vortices supports pocket of Caribbean dry air. As both upper vortices gradually weaken (as all cut-off upper vortices do)...a southern and western Caribbean upper ridge continues building in their wake. Scattered t-storms across the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific is supported by outflow of this building upper ridge. Yet another upper ridge persists in relatively higher pressures east of these upper vortices...located across the eastern tropical Atlantic. The east end of this eastern tropical Atlantic upper ridge is de-amplified by a pair of upper vortices that have been dropped off by paragraph P2 upper trough (Even though I have no satellite-derived 200 mb (upper wind) barbs in this area from the GOES-E satellite outage...the upper vortex NW of the Cape Verde Islands is confirmed by Meteosat-9 water vapor imagery...and both upper vortices are confirmed by looking at initialization of 1200Z and 1800Z GFS model 200 mb fields).

P5...W Atlantic upper ridge is shifting southward in advance of large-scale paragraph P1 upper troughing pushing in. Disturbance Invest 97-L over the eastern Bahamas...supported by the upper outflow of this upper ridge...has gotten a little better organized with curved cloud bands while the surface low (now 1008 mb) is more embedded in the t-storm cluster (albeit the surface low is still on the south edge of the t-storm cluster). Expect this disturbance to continue drifting westward while steered by a merger of the 1028 mb central US surface ridge (paragraph P1) and W Atlantic surface ridge (paragraph P2). The t-storm activity has been intermittent rather than persistent...and the continued westward drift will bring the disturbance increasingly into hostile westerly vertical shear delivered by paragraph P1 upper troughing. These reasons are why I am not upgrading this disturbance to a special feature on this blog.

P6...Disturbed weather across the Bay of Campeche...southern Gulf of Mexico...at times overspreading Florida (mentioned in paragraph P8 of previous discussion #126) remains supported by eastern divergence of paragraph P1 upper troughing. Surface forcing for this area of weather is also coming from cold front extending from 984 mb center in paragraph P1...and coming from surface trough in the Bay of Campeche. The Bay of Campeche surface trough is formerly the tropical wave mentioned in paragraph P9 of previous discussion #126.

P7...Tropical wave moving across the eastern Caribbean in the previous discussion has crossed the central Caribbean and is about to enter the western Caribbean. It is currently suppressed by pocket of dry air mentioned in paragraph P4.

P8...I had been tracking a westward-moving t-storm cluster in Meteosat-9 infrared satellite animation...and marking it as a suspect tropical wave. Although the t-storm cluster has disappeared since 1200Z October 5...I am still marking the suspect tropical wave for continuity's sake...which I believe this evening is positioned in the open tropical Atlantic midway between the Cape Verde Islands and Lesser Antilles.

P9...Tropical wave with 1010 mb low pressure spin in the eastern Atlantic...SW of the Cape Verde Islands...has not gotten any better organized in the last 24 hours. It continues to be enhanced by upper outflow of paragraph P4 eastern tropical Atlantic upper ridge...and so far has managed to avoid oppressive effects of pair of upper vortices that have de-amplified the east end of this upper ridge. This is because the tropical wave is in between both upper vortices. Based on animation of this evening's 1800Z GFS model...this tropical wave should continue west...and has about 48 hours to develop before encountering hostile westerly vertical shear by 72 hours delivered by the pair of cut-off upper vortices mentioned in paragraph P4.

Updated: 4:02 AM GMT on October 08, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #126

By: NCHurricane2009, 4:11 AM GMT on October 07, 2012

...OCTOBER 7 2012...12:11 AM EDT...
An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

In the western part of the Atlantic tropical basin...disturbed weather south of Bermuda has been intensifying and is now upgraded to Invest 97-L. This disturbed weather has developed in part due to a western Atlantic upper ridge (paragraph P7 below and paragraph P8 of previous discussion #125). Meanwhile...upper outflow of a southern Caribbean upper ridge has supported intermittent t-storms in the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific (paragraph P6 below and paragraph P7 of previous discussion #125). The surface low of Invest 97-L...the surface tropical waves in paragraphs P9 and P10...and the melding together of the southern Caribbean and western Atlantic upper ridges shown in models...suggest the potential for some sort of broad tropical disturbance to emerge in this area...although there is no specific computer model support at this time. I believe such a broad tropical disturbance would drift westward while steered by a merger of the 1033 mb central US surface ridge (paragraph P1) and developing west Atlantic surface ridge (paragraph P3).

In the eastern part of the tropical Atlantic basin...a tropical wave that has recently emerged from Africa is becoming better organized. See paragraph P12 below for details on its window of opportunity.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1926Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper vortex over south-central Canada has absorbed all shortwave upper troughs to the south and east mentioned in paragraph P2 of previous discussion #125. This upper vortex...along with the 1004 mb surface depression below it and 1000 mb depression to the east...have all shifted NE into eastern Canada in the last 24 hrs. The 1004 mb and 1000 mb centers have intensified to 994 and 993 mb...respectively...while tapping into eastern divergence supplied by the upper vortex. Western convergence of this upper vortex continues supporting strong central US surface ridge (now 1033 mb) that continues driving in unseasonably cold air. This western upper convergence also supports a band of dry air in northern Mexico and the western Gulf of Mexico.

P2...Surface 1010 mb low north of Bermuda in the previous discussion has dissipated.

P3...Deep-layered cyclone is shifting from the central to eastern open Atlantic. Upper-levels of this system continues to be marked by impressive upper trough recently becoming re-enforced by Atlantic Canada shortwave mentioned in paragraph P2 of previous discussion #125. Western convergence of this upper trough is supporting a gradually developing W Atlantic surface ridge...as the eastern US surface ridge (paragraph P2 previous discussion #125) and 1020 mb surface ridge offshore of Newfoundland (paragraph P2 previous discussion #125) combine. Surface center of the deep-layered cyclone is maintaining strength below 988 mb as it taps into eastern upper divergence of the upper trough. This strong surface center is moving into the Azores this evening.

P4...Based on Meteosat-9 animation over the last day...shortwave upper trough heading toward western Europe in the previous discussion (marked in upper-right corner of above atmo chart) has made it to the British Isles. Western convergence of the upper trough activity in this area continues driving NE Atlantic surface ridge....which now extends hundreds of miles SW to a 1012 mb center. This extension is supported by upper convergence between eastern tropical Atlantic upper ridge in paragraph P6 and upper trough in paragraph P3.

P5...During the previous discussion...remnant non-tropical low of Nadine was turning eastward toward the British Isles while hitching a ride with paragraph P4 shortwave upper trough. Meteosat-9 infrared satellite animation over the last day suggests the remnant low lost its identity before reaching land.

...TROPICAL BELT DISCUSSION...
P6...Central tropical Atlantic upper vortex persists...still extending to a smaller upper vortex near Jamaica and Haiti. Upper convergence on west side of both upper vortices supports pocket of W Caribbean dry air. As both upper vortices gradually weaken (as all cut-off upper vortices do)...a southern and western Caribbean upper ridge continues building in their wake. Another round of t-storms across the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific is supported by outflow of this building upper ridge. Yet another upper ridge persists in relatively higher pressures east of these upper vortices...located across the eastern tropical Atlantic. This eastern tropical Atlantic upper ridge is split in half by cut-off upper vortex delivered by paragraph P3 upper trough.

P7...W Atlantic upper ridge is shifting southward in advance of large-scale paragraph P1 upper vortex pushing in. Disturbed weather south of Bermuda (supported by split flow upper divergence between this upper ridge and paragraph P6 central tropical Atlantic upper vortex) has likewise shifted southward toward the northern Caribbean Islands and eastern Bahamas. Outflow of the upper ridge is further enhancing the t-storm activity of this disturbed weather...which has caused its upgrade to disturbance Invest 97-L. However...the t-storm activity has been intermittent rather than persistent...and the surface low pressure area (now 1007 mb) is to the southeast of the t-storm cluster rather than under it. These reasons...along with lack of computer model support...are why I am not upgrading this disturbance to a special feature on this blog.

P8...A surface trough and t-storm activity in the southern Gulf of Mexico and Bay of Campeche was mentioned in paragraph P9 of previous discussion #125...supported by eastern divergence of southernmost shortwave upper trough in paragraph P2 of previous discussion #125. With all such shortwave upper troughs now absorbed by paragraph P1 upper vortex...this area of weather is now supported by eastern divergence supplied by the large-scale upper vortex. Although the surface trough in the southern Gulf and Bay of Campeche has diminished due to building 1033 mb central US surface ridge (paragraph P1)...there is another surface trough being marked over eastern Florida today.

P9...Tropical wave moving into the central Caribbean in the previous discussion is now entering the western Caribbean. The northern half of the wave is suppressed by pocket of dry air mentioned in paragraph P6...while the southern half maybe aiding in the t-storm activity over the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific described in paragraph P6.

P10...Tropical wave moving across the Lesser Antilles in the previous discussion is now in the eastern Caribbean Sea. It is suppressed by non-divergent and shearing upper westerlies on the south sides of the two upper vortices mentioned in paragraph P6. All of the t-storms it produced yesterday remains left behind...supported by the eastern divergence of the easternmost upper vortex. While these t-storms remain curved and organized at a location just NE of the Lesser Antilles...this organization is occurring about the easternmost upper vortex rather than the surface tropical wave. However...there is a surface trough below the easternmost upper vortex...perhaps a northern fracture left behind by this tropical wave.

P11...I had been tracking a westward-moving t-storm cluster in Meteosat-9 infrared satellite animation...and marking it as a suspect tropical wave. Although the t-storm cluster has disappeared since 1200Z October 5...I am still marking the suspect tropical wave for continuity's sake...which I believe this evening is positioned in the open tropical Atlantic midway between the Cape Verde Islands and Lesser Antilles.

P12...The tropical wave that moved offshore from Africa in the previous discussion is becoming better organized and has developed a 1010 mb low pressure spin while passing south and SW of the Cape Verde Islands. It is becoming enhanced by upper outflow of paragraph P6 eastern tropical Atlantic upper ridge. Based on animation of this evening's 1800Z GFS model...this tropical wave should continue west...and has about 72 hours to develop before encountering hostile westerly vertical shear by 96 hours delivered by the pair of cut-off upper vortices mentioned in paragraph P6.

Updated: 4:04 AM GMT on October 08, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #125

By: NCHurricane2009, 7:24 AM GMT on October 06, 2012

...OCTOBER 6 2012...3:30 AM EDT...
The text in this discussion is about 48 hours after previous discussion #124. The birdseye view charts below are about 36 hours after those in previous discussion #124.

An outage persists with GOES-E satellite imagery in the last several days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

Nadine and Oscar have become remnant systems as previously anticipated. See paragraphs P6 and P13 for update statements on the remnants of these two tropical cyclones.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1912Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough from W Canada has amplified significantly into an upper vortex currently over south-central Canada...thanks to impressive cold air advection from strong surface ridge over the central US and W Canada it supports with its western convergence...and thanks to cold air advection from frontal depression its supports with its eastern divergence. This frontal depression was 1004 mb over the central US in the previous discussion...and now is still 1004 mb while whirling into south-central Canada beneath the upper vortex. A 1000 mb frontal depression is just to the east...formerly the Great Lakes surface cyclone in paragraph P2 of previous discussion #124...and now supported by eastern divergence of the upper vortex.

P2...Major upper trough from central North America remains split into a few features ahead of the paragraph P1 upper vortex. Western convergence of the southernmost split is driving dry air over the SW US and W Gulf of Mexico...and a 1018 mb surface ridge over Arizona. The eastern divergence of a shortwave upper trough over Atlantic Canada is driving a batch of clouds over Newfoundland. The eastern divergence of northernmost shortwave upper trough (not seen in above atmo chart) continues driving a surface cold front eastward across southern Greenland (cold front marked in top-center of above atmo chart)...and western convergence of this same upper shortwave drives 1020 mb surface ridge just offshore of Newfoundland. Southerly flow from the paragraph P8 W Atlantic upper ridge converges with the westerly flow ahead of the upper troughs mentioned in this paragraph...this upper convergence driving a surface 1020 mb ridge over the eastern US.

P3...A surface 1010 mb low is marked just north of Bermuda this early morning...which is a decay of the old cold front associated with surface cyclone from the Great Lakes mentioned in paragraph P1 above (and mentioned in paragraph P2 of previous discussion #124).

P4...Deep-layered cyclone has moved east-southeast from offshore of Atlantic Canada and into the central Atlantic while its upper trough dug SE to the east of the paragraph P8 W Atlantic upper ridge. Surface center of the cyclone strengthened from 992 to 984 mb since previous discussion #124...as the surface center continues to tap into eastern upper divergence of the upper trough. This strong surface cyclone is centered west of the Azores this early morning.

P5...Based on Meteosat-9 animation over the last 48 hours...upper trough has moved into western Europe and out of the scope of the above atmo chart. However...the same satellite animation suggests a second shortwave upper trough is pivoting southeastward on the back side of the previous upper trough...also headed toward western Europe and marked in upper-right corner of above atmo chart. Western convergence of the upper trough activity in this area continues driving NE Atlantic surface ridge.

P6...Since previous discussion #124...Nadine became extratropical (non-tropical) while moving NE across the Azores and into the open NE Atlantic. Satellite animation of Meteosat-9 over the last 48 hours suggests the remnant of Nadine became very well-defined while receiving supportive upper divergence from the east side of the paragraph P4 upper trough. The remnant is recently becoming less-defined in Meteosat-9...but Meteosat-9 suggests the remnant is turning eastward toward the British Isles while hitching a ride with paragraph P5 upper shortwave currently heading toward W Europe.

...TROPICAL BELT DISCUSSION...
P7...Central tropical Atlantic upper vortex persists...while its old SW fragment retrograded about paragraph P7 W Atlantic upper ridge and is now a central Caribbean upper vortex near Jamaica. As both upper vortices gradually weaken (as all cut-off upper vortices do)...a southern Caribbean upper ridge is building in their wake...and a W Caribbean upper ridge has also built in relatively higher pressures between the Jamaica upper vortex and southernmost upper trough in paragraph P2. Yet another upper ridge persists in relatively higher pressures east of these upper vortices...located across the eastern tropical Atlantic. Upper outflow of the aforementioned southern Caribbean upper ridge supported t-storms across the south-central Caribbean...Panama..Costa Rica...and a portion of the eastern Pacific...but these t-storms have recently dwindled.

P8...W Atlantic upper ridge persists while supported by low-level warm air advection ahead of the paragraph P1 1000 mb frontal cyclone that moved from the Great Lakes into south-central Canada. Split flow upper divergence between south edge of this upper ridge and north edge of paragraph P7 central tropical Atlantic upper vortex supports a batch of t-storms and a developing surface trough south of Bermuda.

P9...A surface trough is currently in the southern Gulf of Mexico and Bay of Campeche...which is a decay of the old cold front associated with surface cyclone from the Great Lakes mentioned in paragraph P1 above (and mentioned in paragraph P2 of previous discussion #124). T-storm activity of the surface trough is supported by eastern divergence of southernmost upper trough mentioned in paragraph P2 above...but SW vertical shear from the same upper trough is preventing tropical development from this feature.

P10...Tropical wave moving into the eastern Caribbean in the previous discussion is now entering the central Caribbean.

P11...NHC TAFB recently added a tropical wave moving across the Lesser Antilles since the previous discussion. I suspect this tropical wave originated from Africa and was too poorly-defined for TAFB to mark it until recently. Eastern divergence from paragraph P7 central tropical Atlantic upper vortex is assisting in creating t-storms. While the t-storms have recently become curved and better organized at a location just NE of the Lesser Antilles...this organization is occurring about the upper vortex rather than the surface tropical wave.

P12...By continuing to track a westward-moving cluster of t-storms using Meteosat-9 infrared satellite...I have continued marking a suspect tropical wave which I believe this early morning is positioned in the open tropical Atlantic to the south of Oscar's remnant.

P13...As expected...Tropical Storm Oscar in the eastern tropical Atlantic turned eastward in westerly flow on south side of the paragraph P4 deep-layered cyclone...and is no longer a tropical cyclone while its low pressure field loses its identity in the vast low pressure field of the cyclone. It is worth noting that the NHC track and intensity forecast in previous discussion #124 did very well...while my track and intensity forecast during that time has larger error.

P14...NHC TAFB has added a tropical wave that has recently moved offshore from Africa..marked just SE of the Cape Verde Islands. Meteosat-9 shows associated t-storm cluster just south of the Cape Verde Islands.

Updated: 4:07 AM GMT on October 08, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #124

By: NCHurricane2009, 10:54 AM GMT on October 04, 2012

...OCTOBER 4 2012...6:55 AM EDT...
An outage persists with GOES-E satellite imagery in the last ten days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the temporary GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

Tropical Storm Nadine moving northeastward across the Azores this morning while becoming increasingly indistinct on satellite imagery within the cold front cloud band of a non-tropical system (paragraph P3) coming in from the west. Therefore...Nadine should become non-tropical later this afternoon after pulling away from the Azores. A tropical storm warning remains in effect for the Azores...but will be dropped later today after weather conditions improve. Up to the minute latest info on Nadine...including status of warnings...can be found under the public advisory of Nadine under www.nhc.noaa.gov. Also see Nadine special feature section below for details.

Tropical wave Invest 96-L in the eastern Atlantic has become tropical depression fifteen...then Tropical Storm Oscar...in the last 24 hours. Oscar should continue turning northward into the open Atlantic. See Oscar special feature section below for additional details on this system.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0128Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM NADINE...
Fairly excited about my previous track forecast...which correctly had a righward bias with respect to NHC's such that the center passes over the central Azores. Therefore...my track forecast in Figure 1 is a continuation of my previous...which still has an ever-so-slight rightward bias with the updated NHC track forecast at 5 AM EDT. This is further supported by the slight rightward angle that the most recent segment of NHC recorded storm track has with respect to the 5 AM EDT NHC track forecast. Nadine is currently hooking northward within the east side of the paragraph P3 weather system...and will sooner or later merge with the cold front of the system. In fact...she no longer has her own distinct cloud field and is mixed in with the cold front's cloud band. Therefore...I do agree with the NHC on Nadine becoming non-tropical by 12 hours...and also agree with Nadine maintaining her current strength thru her transition to non-tropical as she gets supportive upper divergence on the east side of the paragraph P3 upper trough.


Figure 1: My forecast for Tropical Storm Nadine generated at 5 AM EDT this morning.

Impact swath in Figure 1 is based on extrapolating the 5 AM EDT tropical storm wind radius along my forecast track. No longer mentioning enhanced rainfall within the impact swath as her cloud/precip field is no longer separable from that of the cold front's. Therefore...their will be rainfall both inside and outside of the impact swath...all associated with the cold front and not directly associated with Nadine.

...SPECIAL FEATURE...TROPICAL STORM OSCAR...
The strong tropical wave in the eastern Atlantic...Invest 96-L...has continued to be enhanced by upper outflow of paragraph P5 East Atlantic upper ridge such that it has strengthened progressively into Tropical Storm Oscar. The tropical storm is moving northward into a break in the subtropical ridge induced by the paragraph P3 weather system...between the paragraph P4 low-level ridge to the NE and paragraph P5 1024 mb low-level ridge to the NW. As such...the tropical storm has already left the favorable upper ridge that allowed for its genesis...and is suffering from westerly vertical shear on the north side of this upper ridge. The sheared structure is well-defined in satellite imagery this morning...with a circular storm mass displaced eastward from the surface swirl center.

The NHC solution in Figure 2 is to soon hook Oscar eastward in westerly flow on the south side of the paragraph P3 weather system. The NHC intensity forecast shows Oscar maintaining strength or getting a little stronger despite the shear...as the NHC track allows Oscar to move ahead of the paragraph P3 upper trough and take advantage of eastern divergence supplied by the upper trough. Based on the 00Z GFS model's representation of the SW lobe of the paragraph P4 low-level ridge (which would seem to me to block eastward motion of Oscar for about 24 more hours)...and the fact that the NHC recorded storm track has a leftward angle with respect to the NHC track forecast...my track forecast in Figure 2 has quiet a leftward bias with respect to the NHC's. As such...I prefer to weaken Oscar in the westerly shear as my track forecast keeps him just west of the favorable eastern divergence of the paragraph P3 upper trough that would otherwise help him. The models...the NHC..and I agree that Oscar should dissipate into a surface trough in the next 36 to 48 hours as Oscar loses his identity within the vast low pressure field of the paragraph P3 weather system.


Figure 2: My forecast for Tropical Storm Oscar generated at 6 AM EDT this morning.

Impact swath in Figure 2 is based on the tropical storm wind field shown in the NHC 5 AM EDT Oscar advisory package...because I think this wind field well-represents the sheared nature of the storm. The wind field is extrapolated along my forecast track to generate the swath. The swath is more symmetric about the storm track toward the end of the forecast because a NE-tracking tropical storm in a westerly shear environment has its impacts occur symmetrically about the storm track.

...MID-LATITUDES DISCUSSION...
P1...A shortwave upper trough continues entering the top-left corner of the above atmo chart from W Canada. Its western convergence supports a strong surface ridge over the NW US and W Canada delivering unseasonably cold air. Its eastern divergence supports surface frontal activity. The Canadian 993 mb frontal cyclone has weakened due to the strength of the aforementioned surface ridge...and now the dominant feature on the front is a 1004 mb depression over the central US. This frontal depression is delivering bouts of winter weather across the northern edge of the US and southern edge of Canada.

P2...Major upper trough over central North America remains split. Western convergence of the southern split is driving dry air over the SW US and W Gulf of Mexico. The eastern divergence of the northern split continues driving a frontal cyclone eastward across north Canada that is moving offshore and toward Greenland (cyclone's surface cold front is seen in top-center of above atmo chart). Eastern divergence of the southern split is driving a 1014 to 1016 mb frontal cyclone that has moved NNE into the Great Lakes from the eastern US. Easterly flow from the paragraph P6 W Atlantic upper ridge converges with the southerly flow ahead of the southern split upper trough...this upper convergence driving a surface 1021 mb ridge over the eastern US.

P3...Deep-layered cyclone moving eastward across the north Atlantic and toward Tropical Storm Nadine. The upper-layer of the cyclone remains an upper trough axis while the surface center has strengthened from 996 to 992 mb in the last 24 hrs...perhaps as the surface center continues to tap into eastern upper divergence of the upper trough. However...the surface center remains tucked below the less-divergent upper trough axis itself...so expect the surface center to not undergo significant strengthening or weaken.

P4...Upper trough continues moving east from the Atlantic high seas and into western Europe. Western convergence of the upper trough continues driving NE Atlantic surface ridge.

...TROPICAL BELT DISCUSSION...
P5...Central tropical Atlantic upper vortex persists...while its SW portion has broke off into a retrograding upper vortex moving across Caribbean Sea in the last 48 hours while steered by W Atlantic upper ridge in paragraph P6. NW convergence of the upper vortex supports 1024 mb W Atlantic surface ridge and a slot of dry air. In relatively higher pressures east of this upper vortex...upper ridge remains built across the eastern tropical Atlantic...further supported by t-storm latent heat release Tropical Storm Oscar

P6...W Atlantic upper ridge persists while supported by low-level warm air advection ahead of the paragraph P2 Great Lakes surface frontal cyclone.

P7...Tropical wave nearing the Lesser Antilles in the previous discussion is now crossing the islands into the eastern Caribbean Sea this morning. Its t-storm activity has reduced...and is suppressed from tropical development by SW vertical shear from the paragraph P5 central Atlantic upper vortex.

P8...By tracking a westward-moving cluster of t-storms in Meteosat-9 infrared satellite...I have continued marking a suspect tropical wave which I believe this morning is positioned SW of the Cape Verde Islands and well SE of Tropical Storm Oscar.

Updated: 6:35 AM GMT on October 06, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #123

By: NCHurricane2009, 7:34 AM GMT on October 03, 2012

...OCTOBER 3 2012...3:40 AM EDT...
An outage persists with GOES-E satellite imagery in the last nine days. GOES-W has been extended to cover much of the view in the two birdseye charts below. The east edge of the temporary GOES-W scan has been adjusted such that its previous bias for showing false cloud tops has been mitigated...and therefore the east edge of the two birdseye charts below are left unrepaired by me. However...I added a Meteosat-9 graft in the lower-right corner of the atmospheric features chart...which better shows a suspect tropical wave that has emerged from Africa (paragraph P8).

Tropical Storm Nadine continuing eastward...and should soon turn northeastward toward the Azores and hit with tropical storm conditions later today. A tropical storm warning remains in effect for the Azores...so preparations in this area should be complete or be completed by this morning. Up to the minute latest info on Nadine...including status of warnings...can be found under the public advisory of Nadine under www.nhc.noaa.gov. Also see Nadine special feature section below for details.

Tropical wave Invest 96-L in the eastern Atlantic has become very well organized...and could become a tropical depression or tropical storm at anytime later today. See Invest 96-L special feature section below for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1918Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM NADINE...
Nadine has weakened a bit more in the last 24 hours. Her satellite appearance showed weaker t-storm activity (perhaps due to the cool waters she is over). The t-storm activity also appeared sheared slightly eastward from the center...perhaps as upper northwest winds from the upper ridge ahead of the paragraph P3 weather system moved in. Very recently...the t-storm activity appears to be stronger...perhaps as Nadine is beginning to take advantage of the incoming upper ridge. I speculate that the upper ridge is reducing the shear/supporting her upper outflow...and or Nadine is taking some advantage of split flow upper divergence between the flow around the upper ridge and departing zonal upper westerlies. Little to no weakening is also supported by the end of the forecast...as she transitions into a non-tropical low supported by the eastern divergence of the incoming paragraph P2 upper vortex. After examining Nadine's relationship with the upper vortex in the 00Z GFS model...I firmly believe Nadine will be non-tropical by 42 hours (5 PM Thursday) as she will be well-embedded in the eastern divergence of the paragraph P3 upper trough while racing NE into much cooler waters that should cause her to lose her vertical warm core. With the aforementioned atmospheric mechanisms suggesting little to no weakening thru transition to non-tropical...I do not show any weakening of Nadine as shown in Figure 1. This is also the solution supported by NHC at 11 PM EDT (albiet they slightly weaken Nadine to 45 mph max winds as she becomes non-tropical).


Figure 1: My forecast for Tropical Storm Nadine generated at 2 AM EDT this morning.

Nadine is currently located southwest of the Azores...currently moving east as she responds to westerly flow on the SE quad of the surface cyclone mentioned in paragraph P3. Nadine will eventually hook more northward as the east side of the cyclone pulls her in. Previously I had agreed with the NHC track forecast...and the NHC track forecast has not changed in the last 24 hours. However this time around...as seen in Figure 1...I have a slight rightward bias relative to the NHC's 11 PM EDT track forecast. This is because the most recent segment of the NHC recorded storm track in Figure 1 shows a straight eastward motion rather than the beginnings of a NE track as the 11 PM EDT NHC track forecasts suggests. This means I am forecasting the center of Nadine to be very near or over the central Azores by early Thursday...while the NHC forecasts the center to weave between the western and central Azores.

Impact swath in Figure 1 is based on extrapolating the 11 PM EDT tropical storm wind radius along my forecast track. Although my impact swath for later today and Thursday only covers the central Azores...a slight shift in track one way or the other could easily change this. Therefore...it is important to emphasize that all of the Azores should have acted on the tropical storm warning....which is in effect for all of the Azores. See www.nhc.noaa.gov Nadine public advisories for latest statements on Azores tropical storm warnings.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 96-L...
Satellite imagery continues showing an eastern Atlantic tropical wave with cyclonic turning in its t-storm clouds such that TAFB continues assigning it a surface low pressure spin. NHC TAFB positioned this tropical wave well west-southwest of the Cape Verde Islands as of 1800Z TAFB last afternoon. This tropical wave is continuing to be enhanced by upper outflow of paragraph P5 East Atlantic upper ridge. Moreover...this upper ridge remains in place while re-enforced by this tropical wave's t-storm latent heat release...so tropical cyclone formation from this system appears imminent...especially as the tropical wave has become very well-organized. Therefore I continue to assert that tropical cyclone formation is very likely sometime today.

It appears that this tropical wave is already turning northwestward toward the widening low-level ridge weakness associated with the paragraph P3 weather system. Therefore...expect this system to recurve northward into the open Atlantic waters.

...MID-LATITUDES DISCUSSION...
P1...A shortwave upper trough is entering the top-left corner of the above atmo chart from W Canada. Its eastern divergence supports a vigorous 993 mb surface frontal cyclone.

P2...Major upper trough over central North America has split. Western convergence of the splitting upper trough is driving dry air over the SW US and W Gulf of Mexico...a 1017 mb ridge over Texas...and a 1018 mb ridge just south of Canada's Hudson Bay. The upper trough's northern split is driving a frontal cyclone eastward across Canada (cyclone's surface cold front with 1002 mb depression is seen in top-center of above atmo chart). Southern split of the upper trough is now a cut-off upper vortex over the TX/LA/AK/OK area...whose eastern divergence is driving an impressive surface frontal cyclone moving NE across the eastern US (evaluated at 1005 mb as of 1800Z).

P3...Deep-layered cyclone over the NE US and eastern Canada is shifting eastward into the north Atlantic and toward Tropical Storm Nadine. The upper-layer of the cyclone is now an amplified upper trough axis while the surface center has strengthened from 1000 to 996 mb in the last 24 hrs. With the surface center now beneath the less-divergent upper trough axis itself...expect the surface center to begin weakening. Western upper convergence of the upper trough supports a 1018 mb surface ridge over the NE US.

P4...Upper trough continues moving east across the Atlantic high seas and is nearing western Europe. Western convergence of the upper trough now drives the 1026 mb NE Atlantic surface ridge mentioned in paragraph P4 of previous discussion #122.

...TROPICAL BELT DISCUSSION...
P5...Central tropical Atlantic upper trough/vortex persists SW of Tropical Storm Nadine...and its SW portion has broke off into a retrograding upper vortex moving across the E Caribbean while steered by W Atlantic upper ridge in paragraph P6. Western convergence of the upper trough/vortex supports 1024 mb W Atlantic surface ridge. In relatively higher pressures southeast of this upper trough/vortex...upper ridge remains built across the eastern tropical Atlantic...further supported by t-storm latent heat release from special feature Invest 96-L.

P6...W Caribbean cut-off upper vortex has lost its identity as the TX/LA/OK/AK upper vortex in paragraph P2 moves in from the NW. W Atlantic upper ridge persists to the east of this...and is propped up by mass low-level warm air advection ahead of the paragraph P2 eastern US surface frontal cyclone. All stormy weather in the W Caribbean area (once supported by split flow upper divergence between the dissipated W Caribbean upper vortex & the upper ridge) has become focused along the cold front of the eastern US cyclone.

P7...Tropical wave midway between the Cape Verdes and Lesser Antilles in the previous discussion is nearing the Lesser Antilles. It continues to produce t-storm activity...supported by upper divergence on the east side of paragraph P5 central Atlantic upper trough. Expect no development from this tropical wave as it gets a dose of southerly and or westerly vertical shear from the upper trough.

P8...Satellite imagery suggests the next tropical has emerged from the west coast of Africa (see lower-right of above atmo chart). The associated t-storm cluster shows some signs of organization...but appears to be biased to the west of the wave axis due to some easterly vertical shear on the south half of the paragraph P5 east Atlantic upper ridge.

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2012 Atlantic Hurricane Season Birdseye Discussion #122

By: NCHurricane2009, 8:12 AM GMT on October 02, 2012

...OCTOBER 2 2012...4:10 AM EDT...
An outage persists with GOES-E satellite imagery in the last eight days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the temporary GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

Nadine weakens to a tropical storm...and is soon to accelerate northeastward for the Azores where tropical storm warnings have been raised. Up to the minute latest info on Nadine...including status of warnings...can be found under the public advisory of Nadine under www.nhc.noaa.gov. Also see Nadine special feature section below for details.

Tropical wave in the eastern Atlantic has become better organized and has been upgraded to Invest 96-L within the last 24 hours...and favorable upper winds are forecast by models to persist with the wave over the next days. Therefore...this tropical wave has been given a special feature section on this blog. See Invest 96-L special feature section below for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1918Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM NADINE...
While getting an expected dose of zonal shearing upper westerlies on SW part of paragraph P3 upper trough...Nadine has been better following the more bullish weakening rate shown by my intensity forecast in previous discussion #120. However...Nadine tonight and this early morning has stopped weakening in an impressive way while re-wrapping its t-storm activity around an eye-like feature. Therefore...I prefer to still follow the less-bullish weakening rate of my previous intensity forecast in discussion #121...and so my intensity points in Figure 1 below are a copy-paste from discussion #121...which means my intensity forecast is more intense than the 11 PM EDT NHC's. My intensity forecast assumes hardly any weakening as the 00Z GFS still shows a shortwave upper ridge ahead of the paragraph P2 weather system coming in from the NW...so I speculate that the upper ridge would reduce shear...and or Nadine taking some advantage of split flow upper divergence between the flow around the upper ridge and departing zonal upper westerlies. Little to no weakening is also supported by the end of the forecast...as she transitions into a non-tropical low supported by the eastern divergence of the incoming paragraph P2 upper vortex. After examining Nadine's relationship with the upper vortex in the 00Z GFS model...I firmly believe Nadine will be non-tropical by 66 hours (5 PM Thursday) as she will be well-embedded in the eastern divergence of the upper vortex and racing NE into much cooler waters that should cause her to lose her vertical warm core.


Figure 1: My forecast for Tropical Storm Nadine generated at 3 AM EDT this morning.

Nadine is currently located southwest of the Azores...finishing a counter-clockwise loop while drifting SE while trapped between the paragraph P4 ridge to the NE and paragraph P5 ridge to the west. Soon...the paragraph P2 vortex will break through...and how sharp Nadine hooks to the north depends on her relative position to the vortex when it breaks through. Any south or west tendencies would mean being embedded in the south side of the vortex (tracking more east than north). Any north or east tendencies would mean being embedded more in the east side of the vortex (tracking more north than east). Because Nadine is further south than I thought she would be at this point...then it would seem I should favor the more east than north solution (i.e. adjust my track to the right of my previous). On the other hand...I thought Nadine would be stalling out between the two ridges by this point...but instead she is showing some east drift (i.e. I should adjust my track to the left of my previous). With one tendency favoring a rightward adjustment and the other a leftward adjustment...I am simply not adjusting anything tonight and maintaining my previous track forecast. However...I do need to favor a faster approach to the Azores than my previous because my previous track did not show the current east drift. Therefore...I like and 100% agree with the current NHC track forecast which is aligned with my previous...but shows a faster approach to the Azores than my previous.

Impact swath in Figure 1 is based on extrapolating the 11 PM EDT tropical storm wind radius along the NHC's forecast track. Although my impact swath for Wednesday and Thursday covers the western and central Azores...a slight shift in track one way or the other could easily change this. Therefore...it is important to emphasize that all of the Azores should be acting on the tropical storm warning....which is in effect for all of the Azores. See www.nhc.noaa.gov Nadine public advisories for latest statements on Azores tropical storm warnings.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 96-L...
Satellite imagery continues showing an eastern Atlantic tropical wave with cyclonic turning in its t-storm clouds such that TAFB continues assigning it a surface low pressure spin. NHC TAFB positioned this tropical wave well west-southwest of the Cape Verde Islands as of 1800Z TAFB last afternoon. This tropical wave is continuing to be enhanced by upper outflow of paragraph P5 East Atlantic upper ridge. Models show this upper ridge remaining in place while re-enforced by this tropical wave's t-storm latent heat release...so tropical cyclone formation from this system is likely...especially as the tropical wave has continued to become better organized. Based on its historic slow rate or organization and its current satellite appearance...my current best guess for tropical cyclone formation is for sometime on Wednesday October 3.

It appears that a tropical cyclone that develops out of this system would first track west while steered by paragraph P4 and P5 Atlantic surface ridges...and then get pulled northward into the open Atlantic by widening weakness between the two ridges generated by paragraph P2 frontal cyclone.

...MID-LATITUDES DISCUSSION...
P1...Major upper trough over western North America has slid east into central North America. Western convergence of the upper trough is driving dry air over the SW US and W Gulf of Mexico...as well as an impressive western US surface ridge. Upper trough's northern half driving a frontal cyclone from W Canada eastward (surface cold front of the cyclone seen in top-left of above atmo chart...located as far south as the north-central US). Southern half of upper trough is driving an impressive frontal cyclone moving ENE across the southeastern US (evaluated at 998 mb as of 1918Z). Because some scattered severe weather continues to be a problem with this cyclone...residents across the SE US and eastern US should visit www.nws.noaa.gov and or listen to local media for latest info on hazardous weather from this system.

P2...Upper vortex over E Canada and the NE US has shifted east and has become vertically stacked with NE US frontal cyclone it supports (evaluated at 1000 mb as of 1918Z)...resulting in a deep-layered cyclone tonight and early this morning. Western upper convergence of deep-layered vortex supports 1014 mb surface ridge over the Great Lakes.

P3...Upper trough continues moving east across the Atlantic high seas. The upper trough's eastern divergence continues supporting a frontal cyclone that has passed well northeast of Tropical Storm Nadine...and has exited the picture while headed for NW Europe. However...this frontal-cyclone's stalled front is marked in the top-center of the above atmo chart.

P4...Impressive ridge in the NE Atlantic persists at 1026 mb in the last 24 hours...and is about to become supported by the western convergence of paragraph P3 upper trough passing by to the north.

...TROPICAL BELT DISCUSSION...
P5...Central tropical Atlantic upper trough/vortex persists SW of Tropical Storm Nadine. Its western convergence supports 1022 mb W Atlantic surface ridge. In relatively higher pressures southeast of this upper trough...upper ridge remains built across the eastern tropical Atlantic...further supported by t-storm latent heat release from special feature Invest 96-L and tropical wave in paragraph P7.

P6...W Caribbean cut-off upper vortex persists. The upper ridges flanking the system to the SW and NE have consolidated into one upper ridge located east of the upper vortex...the upper ridge spanning from the eastern Caribbean northeastward into the W Atlantic and propped up by mass low-level warm air advection ahead of the paragraph P1 and P2 weather systems. Split flow upper divergence between the cut-off upper vortex and upper ridge continues supporting stormy weather in the area...currently located across the W Caribbean...Jamaica...Cayman Islands...and Cuba. Despite the persistence of split flow upper divergence and stormy weather in this area...curiously all surface low pressure features (tropical waves and surface troughs) have dissipated in the last 24 hrs. Therefore...this area continues to be considered a non-threat for tropical development.

P7...Tropical wave midway between the Cape Verdes and Lesser Antilles in the previous discussion is located west of tropical wave Invest 96-L. The eastern half of this wave supports increased t-storms while supported by enhanced upper outflow of paragraph P5 East Atlantic upper ridge. Meanwhile...the west half of the tropical wave is suppressed by hostile southerly vertical shear produced by east side of paragraph P5 Central Atlantic upper trough. Expect no development from this tropical wave as it continues westward in the oppressive environment of the upper trough.

Updated: 9:05 AM GMT on October 02, 2012

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2012 Atlantic Hurricane Season Birdseye Discussion #121

By: NCHurricane2009, 12:44 AM GMT on October 01, 2012

...SEPTEMBER 30 2012...8:50 PM EDT...
An outage persists with GOES-E satellite imagery in the last seven days. GOES-W has been extended to cover much of the view in the two birdseye charts below. However...the east edge of the temporary GOES-W scan has a bias for showing cold cloud tops that are not actually present. Therefore...I have patched the east side of the atmospheric birdseye chart with Meteosat-9 grafts. The east side of the thermodynamics birdseye chart is left unrepaired...so be mindful that the moisture content on the east side of this chart has a positive bias due to the false illusion of cold cloud tops.

Hurricane Nadine maintaining high-end category 1 strength while looping counter-clockwise in the Atlantic subtropics. It is now apparent the Azores are likely to get a strike from Nadine later this week...and therefore interests here should carefully monitor the progress of the storm this week. Since the Azores previously received direct weather from Nadine on September 19 to 21...this will be their second event with this cyclone. See the Nadine special feature section below for details.

As paragraph P1 in the mid-latitudes discussion highlights...a significant upper trough in the mid-latitude westerlies is driving an impressive surface frontal cyclone moving east across the southern US. Its frontal boundary is producing weather in the Gulf of Mexico...but no tropical development is expected. However...some hazardous weather remains possible with this system. See paragraph P1 in the mid-latitudes discussion for details.

A tropical wave in the eastern Atlantic is becoming better organized under favorable upper winds...and the favorable upper winds are forecast by models to persist with the wave over the next days. However...the low pressure spin of the tropical wave so far is not organized enough for imminent tropical cyclone formation. If the low pressure spin indeed becomes better orgainzed...I will be upgrading this to a special feature on this blog. For now...see paragraph P8 in the tropical belt discussion for statement on this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-released HPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...HURRICANE NADINE...
Fairly excited about my previous intensity forecast...which enjoyed 100% accuracy in the last 24 hours while precisely predicting the rate at which Nadine would hit 90 mph max winds today. Nadine continues thriving in a peninsula of favorable upper outflow/upper divergence between the paragraph P3 upper trough passing to the NE and paragraph P5 C Altc upper vortex to the SW. My updated intensity forecast in Figure 1 is similar to my previous...but showing slightly less weakening than my previous due to the fact that Nadine has been holding her strength today a little better than I previously thought. Weakening appears imminent...as the 18Z GFS model insists Nadine's favorable upper outflow becoming squashed out by rather hostile...zonal shearing upper westerlies on the SW side of the paragraph P3 upper trough in the next 24 hours (Monday)...so I forecast a brisk initial weakening rate that makes me fall below the 5 PM EDT NHC intensity forecast. I slow the weakening rate by Tuesday as the 18Z GFS still shows a shortwave upper ridge ahead of the paragraph P2 weather system coming in from the NW...so I speculate that the upper ridge would reduce shear...and or Nadine taking some advantage of split flow upper divergence between the flow around the upper ridge and departing zonal upper westerlies. By the end of the forecast...I stop weakening Nadine as she transitions into a non-tropical low supported by the eastern divergence of the incoming paragraph P2 upper vortex. After examining Nadine's relationship with the upper vortex in the GFS model...I firmly believe Nadine will be non-tropical by 96 hours (Thursday) as she will be well-embedded in the eastern divergence of the upper vortex and racing NE into much cooler waters that should cause her to lose her vertical warm core. On the other hand...the NHC prefers delaying the transition to non-tropical to 120 hours (Friday).


Figure 1: My forecast for Hurricane Nadine generated at 7 PM EDT this evening.

Nadine is currently located southwest of the Azores...performing a counter-clockwise loop while drifting SW and southward in between the paragraph P4 ridge to the NE...paragraph P3 ridge to the NW...and paragraph P5 ridge to the west. I previously did not believe the current SW and south drift was going to happen due to the presence of the paragraph P5 ridge. In hindsight...the paragraph P4 and P3 ridges are stronger than the paragraph P5 ridge...with those two ridges turning Nadine west such that it slammed into the eastern wall of the paragraph P5 ridge. After it slammed into the ridge this afternoon...it is now turning straight southward as seen on satellite animation this evening...thanks to that ridge's eastern northerly flow. With the straight south motion currently observed...I agree with the NHC track forecast on a slow south motion for the next 24 hours. The NHC and models drift Nadine east between 24 and 48 hrs...but given that the 18Z GFS shows all ridges having equal strength and opposing influence by that time...I prefer to keep Nadine instead stationary...creating a westward bias in my position by 48 hours.

For the longer-range...the NHC and models show Nadine reacting to a strong frontal cyclone supported by the incoming paragraph P2 vortex. My previous track forecast had a NE bias relative to NHC for the timeframe that Nadine intersects the frontal cyclone...which meant that my previous solution had Nadine getting caught in the east side of the cyclone such that it tracks more north than east (and this solution caused me to be far north...or left...of the NHC solution). Now...I have a slight W bias relative to NHC for the timeframe that Nadine intersects the frontal cyclone...which now means that my updated track forecast in Figure 1 has Nadine getting caught on the south side of the cyclone such that it tracks more east than north (and now my solution is a little right of the NHC solution). My updated track forecast in Figure 1 now has Nadine's center passing closer to the central Azores...while the NHC's track forecast has Nadine's center passing closer to the western Azores.

Impact swath in Figure 1 is based on extrapolating the 5 PM EDT tropical storm wind radius along my forecast track. Although my impact swath for Wednesday and Thursday barely covers the western Azores and heavily-envelopes the central Azores...a slight shift in track one way or the other could easily change this. Therefore...it is important to emphasize that all of the Azores should be monitoring this situation carefully.

...MID-LATITUDES DISCUSSION...
P1...Major upper trough over western North America continues sliding eastward. Western convergence of the upper trough is driving clearing skies and dry air over Texas...as well as a western US surface ridge. Upper trough's northern half driving a frontal cyclone from W Canada eastward (surface features of the cyclone seen in top-left of above atmo chart). Warm air advection ahead of this frontal cyclone is driving an upper ridge that has shifted from Manitoba to southern Hudson Bay in the last 24 hrs. Southern half of upper trough is driving an impressive frontal cyclone moving east across the southern US from Texas (evaluated at 1001 mb as of 1929Z). Flood watches are posted across parts of Louisiana and Mississippi as of this writing. For the next couple of days...potential exists for flood watches to continue spreading across the US Gulf coast region and SE US. Warm air advection ahead of the frontal cyclone is driving an upper ridge that has shifted from Texas to the Gulf of Mexico in the last 24 hrs. Southerly flow ahead of the frontal cyclone will be in directional vertical shear with respect to westerly flow across the upper ridge...so if enough instability develops from daytime heating...severe t-storm and or tornado watches may also be required in the next couple of days. A tornado watch is currently in effect for parts of Louisiana...Mississippi...Alabama...and the Florida panhandle...and tornado warnings within the watch have been issued. Residents across the SE US and US Gulf coast should visit www.nws.noaa.gov and or listen to local media for latest info on hazardous weather from this system.

P2...Upper trough over E Canada and NE US has amplified further into an upper vortex thanks to amplified upper ridges ahead of the paragraph P1 weather system to the west. Surface 1012 mb frontal depression over the NE US has intensified into a 1003 mb frontal cyclone while taking advantage of eastern peripheral divergence of the upper vortex. Western convergence of this upper vortex supports 1019 to 1024 mb surface ridge centers that have shifted from the central US and into eastern Canada in the last 24 hrs...as well as a slot of drying air wrapping in behind the 1003 mb frontal cyclone.

P3...Upper trough continues moving east across the Atlantic high seas. The upper trough's eastern divergence continues supporting a frontal cyclone that has passed north of Hurricane Nadine...and is exiting the picture while headed for NW Europe. The upper trough's western convergence supports a greater-than-1028 mb ridge center just offshore of Newfoundland. W Caribbean cut-off left behind by this upper trough days ago has been moved to paragraph P6 of the tropical belt discussion below.

P4...Impressive ridge in the NE Atlantic has weakened from 1028 to 1026 mb in the last 24 hours.

...TROPICAL BELT DISCUSSION...
P5...Central tropical Atlantic upper trough/vortex persists SW of Hurricane Nadine. Central Atlantic surface trough & t-storm cluster it generated with its eastern divergence 24 hrs ago has dissipated. However...it has generated a new 1022 to 1023 mb W Atlantic surface ridge with its western convergence. In relatively higher pressures southeast of this upper trough...upper ridge has built across the eastern tropical Atlantic.

P6...W Caribbean tropical wave (discussion #120 paragraph P8)...W Caribbean cut-off upper trough (discussion #120 paragraph P3)...and surface trough passing north of Puerto Rico (discussion #120 paragraph P9) have all combined to make complex weather in this area. The W Caribbean cut-off upper trough is flanked by two upper ridges. The northwestern upper ridge extends into the W Atlantic and is driven by warm air advection ahead of the paragraph P2 frontal cyclone. The southeastern upper ridge has developed in relatively higher pressures SE of the cut-off upper trough and spans the east Caribbean. Upper convergence between the NW upper ridge and cut-off upper trough supports a slot of dry air where the tropical wave is located. Split flow upper divergence between the cut-off upper trough and SE upper ridge supports stormy weather across Jamaica...Cayman Islands...eastern Cuba...Haiti...the eastern Bahamas...as well as the surface trough that has moved from N of Puerto Rico to N of Haiti in the last 24 hrs. Most impressive feature of cut-off upper trough is a well-defined upper vortex spinning in the W Caribbean tonight.

P7...Tropical wave midway between the Cape Verdes and Lesser Antilles in the previous discussion has seen an increase in t-storms while supported by enhanced upper outflow of paragraph P5 East Atlantic upper ridge. However...it is about to enter hostile southerly vertical shear produced by east side of paragraph P5 Central Atlantic upper trough.

P8...Satellite imagery continues showing an eastern Atlantic tropical wave with cyclonic turning in its t-storm clouds such that TAFB assigned it a surface low pressure spin today. NHC TAFB positioned this tropical wave just southwest of the Cape Verde Islands as of 1800Z TAFB this afternoon. Similar to the tropical wave in paragraph P7...this tropical wave is enhanced by upper outflow of paragraph P5 East Atlantic upper ridge. Models show this upper ridge remaining in place while re-enforced by this tropical wave's t-storm latent heat release...so tropical cyclone formation from this system is possible in the next days. It initially appears such a tropical cyclone would first track west while steered by paragraph P4 and P5 Atlantic surface ridges...and then get pulled northward into the open Atlantic by widening weakness between the two ridges generated by paragraph P2 frontal cyclone.

Updated: 7:31 AM GMT on October 02, 2012

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