2012 Atlantic Hurricane Season Birdseye Discussion #145

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

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...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.

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2. WunderAlertBot (Admin)
2:46 AM GMT on October 30, 2012
NCHurricane2009 has created a new entry.
1. KoritheMan
6:53 AM GMT on October 29, 2012
I've never seen an impact swath quite so large. Truly terrifying, this Sandy...
Member Since: March 7, 2007 Posts: 601 Comments: 21199

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