NCHurricane2009's Blog

2012 Atlantic Hurricane Season Birdseye Discussion #38A (Special Update)

By: NCHurricane2009, 11:33 PM GMT on June 28, 2012

...JUNE 28 2012...7:25 PM EDT...
This is a special update from full discussion #38 concerning the remnants of Debby.

The remnants of Debby have turned eastward toward Bermuda while steered by strong surface low located over Nova Scotia mentioned in paragraph P2 of full discussion #38. Even though her satellite appearance is still suggestive of a system entagled along a frontal boundary...she appears to be re-gaining tropical characteristics with more symmetry in her storm clouds. Her satellite apperance and low surface pressures (as analyzed on the NHC TAFB maps) suggest she may have re-gained tropical storm strength since she left Florida...which in part is due to divergence ahead of the east US upper trough (paragraph P2 of full discussion #38). Because she is moving even faster...her shear relative to strong upper southwesterly winds from the east US upper trough has dropped...which explains how her storm clouds have gained symmetrical distribution. Her fast pace continues to defy the speed suggested by my final (and the NHC's final) forecast track back during discussion #37...when Debby was last tropical. The more recent eastward turn began to veer from the NHC's last forecast track and better match mine (which had a southward bias)...but now neither my nor the NHC's last forecast is accurate at this time with the continued eastward movement.

In summary...we can now expect Debby to bring tropical storm-like conditions to Bermuda tomorrow as the center passes over or just north of the island (as estimated in Figure 1 below). I would not be surprised if the National Hurricane Center re-upgrades Debby to a tropical storm later tonight...which would require a sudden tropcial storm warning for Bermuda. The Nova Scotia low's eastward progress is being blocked by strong upper ridging (paragraph P3...discussion #38) and strong surface ridging (paragraph P5...discussion #38). Using the quasi-stationary Nova Scotia low as the steering feature...and using the curvature of clouds about the Nova Scotia low...I estimate the trajectory of Debby will be as shown in Figure 1.

Refer back to discussion #38 for current situation on the rest of the Atlantic tropics.


Figure 1: Current analysis of Debby's situation. Trajectory suggests the center will pass directly or just north of the island of Bermuda.

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #38

By: NCHurricane2009, 11:50 AM GMT on June 28, 2012

...JUNE 28 2012...12:18 PM EDT...
Debby becomes extratropical (non-tropical) much sooner than predicted. See first special feature seciton for further details.

Caribbean tropical wave in paragraph P10 (in the tropical belt discussion) is at less risk for developing.

Tropical wave southwest of the Cape Verde Islands has been upgraded to a special feature on this blog. See second special feature section for further details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1931Z-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...REMNANTS OF DEBBY...
The National Hurricane Center has downgraded Debby to a remnant frontal boundary (non-tropical) low in the last 24 hours. The front attached to the 997 mb cyclone in paragraph P2 has been sagging southward...and Debby as a result has merged with it. As a non-tropical entity...the remnant of Debby is supported by divergence ahead of the upper trough/low mentioned in paragraph P2.

Expect the remnants of Debby to continue northeastward while steered by the southwesterly flow ahead of the system in paragraph P2...and southwesterly flow will be re-enforced by the frontal system in paragraph P1 in the coming days. Her northeastward track is a tad faster than previously forecast by me and the NHC...and is following the NHC's forecast track much closer than my forecast track (which had a southward bias). Debby's remnants will deliver weather to Bermuda (rain with gusty winds possible)...but because she is entagled with the frontal system in paragraph P2...it will be hard to say which is directly Debby's impact and which is the front's. The strongest weather on Debby's northeast half however looks to pass just northwest of Bermuda if current satellite trends continue. Should air mass contrasts diminish across the frontal segment Debby is within...she may be re-upgraded to tropical status at any time now.

...SPECIAL FEATURE...TROPICAL WAVE SOUTHWEST OF CAPE VERDE ISLANDS...
Tropical wave SW of Cape Verde Islands continues to fight off dry air mentioned in paragraph P9...because it has received enhanced poleward upper outflow thanks to upper vorticity embedded in the east Atlantic upper ridge (this upper vorticity also mentioned in paragraph P9). Paragraph P9 also explains how there is plenty of deep-layered easterly flow ahead of this tropical wave...promoting a low shear environment also supportive for development in the coming days. The tropical wave still shows cyclonic banding features...has been upgraded with a 1013 mb low...and the National Hurricane Center continues to gives this a 10% chance of developing in the next 48 hours.

...MID-LATITUDES DISCUSSION...
P1...Warm air advection ahead of surface frontal system in western North America continues to support an upper ridge...which is now moving into the central US. This upper ridge is associated with intense heat that has started over the central US and moving toward the eastern US. The western North America surface frontal system has its strong low pressure in SW Canada. Meanwhile...upper convergence on the east side of the west US upper ridge conitnues supporting dry air.

P2...Frontal system and longwave upper trough over the eastern US has consolidated into an upper low/trough associated with cool air advection of a 998 mb surface cyclone that has made landfall in the Maine/Nova Scotia area..and is currently 997 mb. This 997 mb cyclone should now begin weakening thanks to a much less divergent environment directly below the upper trough/low axis. The cut-off Gulf of Mexico upper vortex that stemmed from this weather system has weakened into a south Texas upper trough while swinging westward about the anticyclonic center of the upper ridge mentioned in paragraph P1. Of final note...upper convergence on the back side of this upper trough supports a 1018 mb ridge over the eastern US that moved southward from the Great Lakes...but this surface ridge will be diminishing once low surface pressures from the frontal system in paragraph P1 arrives.

P3...Upper ridge over the western Atlantic and south Greenland remains supported by warm air advection ahead of the complex frontal system outlined in paragraph P2 above. The eastern convergence of this upper ridge supports surface 1026 mb ridging in the vicinity of Greenland that is connected to the 1030 mb center mentioned in paragraph P5.

P4...Large upper trough in the north-central Atlantic is moving NE toward Europe...and the surface frontal cyclone it once supported is decaying with a lack of divergence beneath the upper trough axis. Position of the surface cyclone in the above birdseye charts is based on satellite imagery since it is outside the scope of the TAFB and HPC analyses. Cut-off upper trough east of Bermuda in the previous discussion continues to be pushed eastward by growing upper ridge mentioned in paragraph P7. It has now arrived into the open central Atlantic.

P5...Open Atlantic surface ridge has 1024 mb center SW of the Azores which has recently grown to 1030 mb and is now NW of the Azores. The 1030 mb center is supported by upper convergence on the back side of the north-central Atlantic upper trough (paragraph P4). South end of north-central Atlantic frontal cyclone's cold front (paragraph P4) has split off into a surface trough retrograding westward around the south side of the 1030 mb center.

P6...1013 mb NE Atlantic surface low (whose formation was described in paragraph P6 of previous discussion) has moved into Spain ahead of the north-central Atlantic weather system in paragraph P4. It has been downgraded to a surface trough.

...TROPICAL BELT DISCUSSION...
P7...Upper ridge over the southern Gulf of Mexico continues to be expansive....and its inflated state is attributed to previous latent heat release from Debby's t-storm clouds. This upper ridge has gone further eastward expansion thanks to warm air advection ahead of complex frontal system outlined in paragraph P2.

P8...Cut-off upper vorticity in the eastern Caribbean has dissipted.

P9...Expansive east Atlantic upper ridge continues. In conjunction with the surface ridge in paragraph P5 and upper ridge in paragraph P7...deep-layered easterly flow exists across much of the Atlantic tropics that is advecting African desert dry air (brown shading in the above thermo birdseye chart) westward. Remaining embedded in the upper ridge is a westward-tracking upper low that has recently weakened to an east-west upper trough.

P10...Tropical wave in the eastern Caribbean Sea in the previous discussion is now in the central Caribbean. It remains suppressed by dry air mentioned in paragraph P9 above. Because the upper vorticity in paragraph P8 has dissipated...the upper divergence between it and the upper ridge in paragraph P7 is gone...and so are the associated t-storms over Panama. With the Panama activity dissipated...this tropical wave's only potential for development is if it gets closer to the favorable low shear/enhanced outflow center of the paragraph P7 upper ridge.

P11...Tropical wave SW of the Cape Verde Islands has been moved to above 2nd special feature section.

Updated: 9:57 PM GMT on June 28, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #37

By: NCHurricane2009, 6:35 AM GMT on June 27, 2012

...JUNE 27 2012...2:40 AM EDT...
Debby weakens to a tropical depression while centered over northern Florida after landfall. See special feature section for updates and forecasts on this situation.

Watching two tropical waves in the Atlantic Ocean for possible development. See paragraphs P10 and P11 (in the tropical belt discussion) for further details.

...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).

...SPECIAL FEATURE...TROPICAL DEPRESSION DEBBY...
This continues to be a complicated situation...and therefore this current discussion of Tropical Depression Debby will be referring to quiet a few paragraph (P) numbers in the mid-latitude and tropical belt discussions below.

My updated track forecast versus the National Hurricane Center's (NHC) is shown in Figure 1 below. Since the previous discussion...Debby has continued eastward in response to the intensification of 998 mb surface low located on an eastern US front mentioned in paragraph P2. In fact...the track has recently been more ESE judging by latest nighttime shortwave infrared satellite...the more southward component perhaps caused by northwesterly flow behind the 998 mb cyclone...and ahead of the western US upper ridge (paragraph P1) and Great Lakes surface ridge (end of paragraph P2). The recent ESE motion makes me predict a forecast track to the right of (or further south) than the NHC's for most of the next 5-days. I maintain the current forward speed for the first 24 hrs (thru 11 PM Wed)...then begin to accelerate Debby faster as the west US upper ridge and Great Lakes surface ridge both get knocked out by incoming west coast frontal system mentioned in paragraph P1. The more northward deflection towards the latter half of the forecast is caused by west end of Atlantic surface ridge (paragraph P5) progged by the models to stay in place thru the forecast period. The very rapid acceleration to the NE by 11 PM Sunday is due to Debby getting caught in what models suggest to be vigorous southwesterly flow ahead of what is now the incoming west coast frontal system and its supporting upper trough.


Figure 1: My current 5-day Tropical Storm Debby forecast this early morning.

Intensity-wise...Debby continues coughing on dry air (source mentioned in paragraph P1)...and continues to be sheared by westerlies on the north side of its former warm core upper ridge (paragraph P7 feature). Combined with the recent north Florida landfall...Debby has weakened to a tropical depression. The only thing keeping Debby alive (as a trpoical cyclone) in this otherwise hostile environment is upper divergence between the northeast corner of the west Gulf of Mexico upper-level low (paragraph P2) and northwest half of the adjacent warm core upper ridge (paragraph P7). As Debby moves further away from the Gulf of Mexico upper low...source of upper divergence shortly will switch to split westerly flow located at the boundary of the warm core upper ridge (paragraph P7) and east US upper troughing (paragraph P2).

If Debby follows the forward pace shown in Figure 1...then the models suggest she will become just ahead of the upper troughing in paragraph P2...which will allow her low-level circulation to advect cooler air behind her and warmer air ahead of her. This would allow Debby to carve out her own amplifying upper trough (extension of the paragraph P2 upper trough) to her west...and amplify a cell of upper ridging (extension of paragraph P7 upper ridge) to her east. The upper wind field shown by the models is divergent at the boundary between the mini upper trough and mini upper ridge...and moreover Debby could easily ventilate herself into the eastern mini upper ridge...all of this suggesting further strengthening by Thursday thru Saturday timeframe. My intensity forecat in Figure 1 is more aggressive than the NHC's current version...as I am gambling she will take good advantage of all these dynamics at waters above or at 26 deg C. After she goes into cooler waters below 26 deg C (judging by above birdseye thermo chart) and gets strong southwesterly shear by Sunday...I weaken Debby at the end of the forecast. If Debby is maintaining strength more than shown by Sunday...this means she is doing so non-tropically while taking advantage of upper divergence ahead of the upper trough she is accelerating with.

5-day forecast impacts in Figure 1 are what I think if Debby follows my forecast. Impact swath is initialized using current Florida radar presentation...then I gradually mold it into the shape I think the storm will have by the 11 AM Saturday position. By 11 AM Saturday...I imagine Debby having clouds biased to her east side as the mini upper trough mentioned in the previous paragraph prevents her from building much t-storms on her west side. By 11 PM Sunday...the thickest clouds should shift to the northeast half of Debby under immense southwesterly shear...so the impact swath becomes symmetrical about the storm track at the very end because the track is also northeastward by that time. The forecast impact swath diameter also shrivels in size at the end as Debby fades over cooler waters/southwesterly shear.

The forecast track and impact swath in Figure 1 suggests that at this time...Debby should pass well west of Bermuda without direct impacts to the island. If the trajectory doesn't lift northward as quickly by late Thursday/early Friday...then maybe the far eastern fringes of her direct impacts could reach the island.

...MID-LATITUDES DISCUSSION...
P1...Warm air advection ahead of surface frontal system hanging off west coast of North America continues supporting the upper ridge over the western US. After the Great Lakes surface ridge (in paragraph P2) has moved out of the way...the west coast frontal system has finally made its way into the western US with a 994 mb low pressure center in eastern Montana. Meanwhile...upper convergence on the east side of the west US upper ridge conitnues supporting dry air.

P2...Frontal system and longwave upper trough over the eastern US is currently complicated. Surface front that was pushing into the NW Atlantic yesterday has dissipated thanks to intensifying 1024 mb center of open Atlantic ridge mentioned in paragraph P5. 24 hrs ago...an east Canada 1000 mb frontal cyclone delivered a surface front reaching into the eastern US. The 1000 mb low is no longer the dominant feature on this front...becoming replaced by a rapidly intensifying 998 mb cyclone moving NE into coastal Maine and Nova Scotia. Locally strong cold air advection behind this 998 mb surface cyclone has carved out an upper vortex that is beginning to align with the surface cyclone. Once this happens...a much less divergent environment beneath the upper vortex will begin weakening the surface cyclone. Cut-off upper vortex (interacting with Tropical Storm Debby) in the western Gulf of Mexico was left behind by this longwave upper trough regime three days ago...but now the cut-off is exiting the Gulf of Mexico while retrograding around the anticyclonic center of the upper ridge in paragraph P1. Of final note...upper convergence on the back side of this longwave upper trough regime supports a SE-moving surface ridge over the Great Lakes who is currently at 1018 mb.

P3...Upper ridge over the western Atlantic and south Greenland remains supported by warm air advection ahead of the complex frontal system outlined in paragraph P2 above. The eastern convergence of this upper ridge supports surface ridging in the vicinity of Greenland that has recently merged with the 1024 mb center mentioned in paragraph P5.

P4...Large upper trough in the north-central Atlantic is moving NE toward Europe...and the surface frontal cyclone it once supported is decaying with a lack of divergence beneath the upper trough axis. From the isobars drawn on the 1800Z TAFB analysis...the surface cyclone is currently below 1016 mb. Cut-off upper trough east of Bermuda in the previous discussion continues to be pushed eastward by growing upper ridge mentioned in paragraph P7.

P5...Open Atlantic surface ridge has a 1021 mb center SE of the Azores and newly-intensifying 1024 mb center SW of the Azores...with the cold front extending from the north-central Atlantic surface cyclone (paragraph P4) spliting the two centers. The 1024 mb center has supportive upper convergence...as upper southwesterlies ahead of the cut-off upper trough E of Bermuda (paragraph P4) converge with upper northwesterlies behind the north-central Atlantic upper trough (also mentioned in paragraph P4).

P6...Highly-amplified cut-off upper vorticity in the NE Atlantic (over the Canayr Islands) has undergone changes in the last 24 hours. The north half has merged with north-central Atlantic upper trough mentioned in paragraph P4...but not before upper divergence ahead of it touched off a 1013 mb surface low and cloud swirl near Spain and Morocco. The southern half has retrograded southwestward around an anticyclonic center of the upper ridge mentioend in paragraph P9.

...TROPICAL BELT DISCUSSION...
P7...Upper ridge over the southern Gulf of Mexico continues to be expansive....and its inflated state is attributed to previous latent heat release from Debby's t-storm clouds. This upper ridge has gone further eastward expansion thanks to warm air adveciton ahead of complex frontal system outlined in paragraph P2.

P8...Cut-off upper vorticity persists in a SW-NE elongation...from the eastern Caribbean to the tropical waters east of the Lesser Antilles. Westerly flow going into the west flank of this vorticity heavily diverges with mainstream easterly flow on the south side of the upper ridge in paragraph P7...resulitng in an increase in t-storms near and over Panama as well as a new surface trough.

P9...Expansive east Atlantic upper ridge continues. In conjunction with the surface ridge in paragraph P5 and upper ridge in paragraph P7...deep-layered easterly flow exists across much of the Atlantic tropics that is advecting African desert dry air (brown shading in the above thermo birdseye chart) westward. A northeastern lobe of this upper ridge had been greatly amplified in the last 48 hours thanks to warm air advection ahead of north-central Atlantic surface cyclone mentioned in paragraph P4. This northeastern lobe has now consolidated into an anticyclonic center southeast of the Azores...and some of the NE Atlantic upper vorticity (paragraph P6) has dived southwestward while moving around this anticyclonic center. The result is that a westward-tracking upper low is now embedded in this east Atlantic upper ridge.

P10...Tropical wave crossing the Lesser Antilles in the previous discussion is now crossing the eastern Caribbean Sea. It remains suppressed by dry air mentioned in paragraph P9 above...but is about to enter the moistening environment and surface trough near Panama (paragraph P8). This tropical wave in the short-term will continue to battle northeasterly shear from the strong upper ridge mentioned in paragraph P7. However...if this tropical wave interacts with the Panama activty and then later gets closer to the favorable low shear/enhanced outflow center of this upper ridge...then we may have something to watch for tropical development later on.

P11...Tropical wave SW of the Cape Verde Islands has been successful in fighting off dry air mentioned in paragraph P9...because it has received enhanced poleward upper outflow thanks to upper vorticity mentioned in paragraph P6. See paragraphs P6 and P9 for how some of this favorable upper vorticity is following the tropical wave as a westward-tracking upper low. The tropical wave has gained some cyclonic banding features (albeit small in size) in its t-storm cloud pattern...and the National Hurricane Center gives this a 10% chance of developing in the next 48 hours while introducing it into their tropical weather outlook in the last 24 hours. If these trends continue...I will be writing a special brief update or be upgrading this to a special feature in my next full discussion.

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #36

By: NCHurricane2009, 6:10 AM GMT on June 26, 2012

...JUNE 26 2012...2:10 AM EDT...
Tropical Storm Debby a flood threat to north Florida and south Georgia. See special feature section for further details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1931Z-released HPC analysis.

In light blue is upper air anlaysis, 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 DEBBY...
This continues to be a complicated situation...and therefore this current discussion of Tropical Storm Debby will be referring to quiet a few paragraph (P) numbers in the mid-latitude and tropical belt discussions below.

My updated track forecast versus the National Hurricane Center's (NHC) is shown in Figure 1 below. Debby has continued going northeastward toward a ridge weakness created by the upper troughing and surface frontal systems mentioned in paragraph P2. Recently...nighttime shortwave infrared satellite imagery suggests an acceleration straight east instead of ENE as the NHC forecast shows...which is why my current forecast track is to the right (or south of) the NHC's. I surmise the recent eastward acceleration is Debby responding to the intensification of surface low pressures located on an eastern US front mentioned in pargraph P2. The earlier NE track and current eastward acceleration suggest the surface ridge diving SE from western Canada into the Great Lakes (end of paragraph P2) is not enough to numb Debby's eastward track toward north Florida and the Atlantic...so now I am depending on upper ridging in paragraph P1 to help later do this. After being initially faster than the NHC forecast track (to account for the recent east acceleration)...I become quiet slower than the NHC forecast track thru Thursday based on when the models think the upper ridge in paragraph P1 will be much closer to Debby (hence when I think this upper ridge will help numb her eastward progress in conjunction with the Great Lakes surface ridge). After the Great Lakes surface ridge and paragraph P1 upper ridge get knocked out by west coast frontal system mentioned in paragraph P1...there is deep-layered westerly flow left behind for Debby to accelerate faster to the east by Friday (which is what I show). By Saturday...I once again slow the forward speed of Debby based on what I think is weak surface ridging re-developing over the Great Lakes (caused by upper convergence on the back side of the shortwave upper trough that supports the incoming west coast frontal system).


Figure 1: My current 5-day Tropical Storm Debby forecast this early morning.

Intensity-wise...yesterday it was wrong to not worry about dry air mentioned in paragraph P1. I was expecting the tremendous upper outflow of Debby to keep low-level lift and moistening such that the dry air wouldn't penetrate...especially as the upper outflow would become more symmetrical as the west Gulf upper-level low (ULL) in paragraph P2 retrogrades westward and away (as the ULL moves about the anticyclonic center of the upper ridge in paragraph P1). But indeed...dry air has weakened Debby. Moreover...the warm core upper ridge/outflow of Debby (paragraph P7) has been pushed southward...as the eastern US frontal system and its upper trough (paragraph P2) appear to be amplifying to Debby's north at this hour. This has exposed Debby to westerly shear on the north side of the warm core upper ridge. I believe what is keeping Debby from collapsing under the dry air and westerly shear is supportive upper divergence located between the NE corner of the west Gulf ULL and NW edge of the warm core upper ridge.

I expect Debby to continue maintaining strength from said upper divergence thru landfall time...then weaken to a 35 mph max wind tropical depression over north Florida. The long time over land shown by my Figure 1 forecast would seem to suggest dissipation...but Debby has been a rather large tropical cyclone where I believe its offshore cloud bands over water will continue feeding latent heat release to Debby such that she is still a tropical cyclone all this time. Re-strengthening back to a tropical storm by Friday and Saturday (once she goes slowly into the Atlantic) is possible...with models suggesting the paragraph P7 warm core upper ridge re-building northward (near or over Debby)...after this upper ridge re-gains real estate behind the exiting paragraph P2 upper trough.

5-day forecast impacts in Figure 1 are what I think if Debby follows my forecast. Mention of isolated tornadoes is due to the many tornado warnings we have seen in south and central Florida in the last two days...but this is also a reminder that Debby could produce isolated tornadoes throughout the entire forecast period (as tropical cyclones are typically capable of). Impact swath is drawn based on the initial lopsided structure caused by westerly vertical shear...and then taking that sheared structure eastward along the forecast track. Width/shape of impact swath is a combo of looking at current radar and the NHC's 10 PM CDT tropical storm wind field. Current radar suggests potential for major flooding problems in northern Florida and southern Georgia...especially if Debby maintains her current radar presentation while following the rather slow eastward track I presented in Figure 1 above.

...MID-LATITUDES DISCUSSION...
P1...Warm air advection ahead of surface frontal system hanging off west coast of North America continues supporting the upper ridge over the western US. Eastward progression of west coast surface system is currently blocked by strong surface ridge entering the Great Lakes region and mentioned in paragraph P2. Meanwhile...upper convergence on the east side of the west US upper ridge supports dry air.

P2...Frontal system and longwave upper trough over the eastern US is currently complicated. Surface front near the east coasts of the US and Canada is pushing into the NW Atlantic...with a 1010 mb center over SE Canada. 1004 mb frontal cyclone on the east coast of Hudson Bay is now 1000 mb over eastern Canada while delivering another front reaching into the eastern US. 48 hrs ago this longwave upper trough regime had left behind a cut-off upper vortex (interacting with Tropical Storm Debby) in the western Gulf of Mexico...and this cut-off feature still persists. Of final note...upper convergence on the back side of this longwave upper trough regime supports a strong west Canada surface ridge that is diving southeast into the Great Lakes region with a 1023 mb center.

P3...Upper ridge over the western Atlantic and south Greenland remains supported by warm air advection ahead of the complex frontal system outlined in paragraph P2 above. The eastern convergence of this upper ridge supports a 1023 mb surface ridge in the vicinity of south Greenland.

P4...Large upper vortex in the north-central Atlantic has weakened into an upper trough...and the surface frontal cyclone it once supported is decaying with a lack of divergence beneath the upper trough axis. From the isobars drawn on the 1200Z TAFB analysis...the surface cyclone is currently below 1012 mb. Cut-off upper vortex south of Bermuda in the previous discussion continues to be pushed eastward by Debby's sprawling warm core upper ridge...and is now east of Bermuda while it too has weakened to an upper trough.

P5...Open Atlantic surface ridge has a 1022 mb center NE of the Azores that is supported with upper convergence NE of the E Atlantic upper ridge (paragraph P9) and W of the NE Atlantic upper vorticity (paragraph P6). This surface ridge also has a 1019 mb center south of the north-central Atlantic surface cyclone (paragraph P4)...and a 1021 mb center east of Bermuda.

P6...Highly-amplified cut-off upper trough in the NE Atlantic (over the Canayr Islands) has amplified even further into upper low vortices. The amplification of this cut-off fragment is due to equal amplification of the east Atlantic upper ridge (paragraph P9) to its southwest. Divergence on the east side of this cut-off upper voriticity continues to support cloudiness that has expanded from the Moroccan coast in the last 24 hours...and now this cloudiness has the signature of a surface low pressure swirl and also reaches into southern Spain. This swirl of clouds has been upgraded to a surface trough per 1800Z TAFB analysis.

...TROPICAL BELT DISCUSSION...
P7...Upper ridge over the southern Gulf of Mexico continues to sprawl with the support of Tropical Storm Debby's thunderstorm latent heat release. This upper ridge used to support the outflow of Debby...but now Debby's surface center is on the north side of this upper ridge as Debby has been moving northeastward per special feature section above. The result is Debby is now under westerly vertical shear on the north side of this upper ridge.

P8...Cut-off upper vorticity persists in a SW-NE elongation...from the eastern Caribbean to the tropical waters east of the Lesser Antilles.

P9...Expansive east Atlantic upper ridge continues. In conjunction with the surface ridge in paragraph P5...deep-layered easterly flow exists south of this upper ridge such that dry air from the African desert is being advected westward across the Atlantic tropics (brown shading in the above thermo birdseye chart). A northeastern lobe of this upper ridge has greatly amplified in the last 24 hours thanks to warm air advection ahead of north-central Atlantic cyclone in paragraph P4. As explained in paragraph P6...this amplified northeastern lobe has caused equal amplification of NE Atlantic upper vorticity...and in turn the amplifying upper vorticity has dug southward and pushed the main body of this upper ridge westward.

P10...Tropical wave midway between the Cape Verde Islands and Lesser Antilles in the previous discussion is now crossing the Lesser Antilles in this discussion. It remains suppressed by dry air mentioned in paragraph P9 above...but is about to enter the southern reaches of the upper ridge mentioned in paragraph P7. This upper ridge was a manifestation of Debby's warm core upper outflow...and as a result some of the moist air from Debby's cloud tops have been advected southward and into the environment this tropical wave is about to cross. Although moistening air is "good news" for this tropical wave...it will in the short-term have to battle northeasterly shear from this same upper ridge. However...if this tropical wave gets closer to the favorable low shear/enhanced outflow center of this upper ridge...then we may have something to watch for tropical development later on.

P11...Tropical wave south of the Cape Verde Islands in the previous discussion is now SW of the islands. If the tropical wave in paragraph P10 is any indication...this tropical wave should also succumb to the dry air mentioned in paragraph P9. However...this tropical wave has been better fighting the dry air than its predecessor in paragraph P10...because it has received enhanced poleward upper outflow thanks to upper vorticity mentioned in paragraph P6. As the tropical wave moved away from this upper vorticity...I expect it to begin suffering from the dry air.

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #35

By: NCHurricane2009, 9:20 PM GMT on June 24, 2012

...JUNE 24 2012...5:20 PM EDT...
Tropical Storm Debby uncertain at this hour...but is lashing Florida with tornado warnings...heavy flooding rains...and gusty (and potentially damaging) winds as one gets closer to the storm center. Interests along the United States north Gulf coast should keep monitoring Debby. In case the storm tracks northeastward into the Atlantic...interests along the Georgia and Carolina coasts should also monitor Debby. See special feature section for additional details.

Next full update on this blog may not come until very late tomorrow evening...because of my work schedule. If Debby's behavior changes signficantly from the forecasts indicated in Figure 1 in the special features section...I will write special brief updates before then.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1325Z-released HPC analysis.

In light blue is upper air anlaysis, 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 DEBBY...
This is a complicated situation...and therefore this current discussion of Tropical Storm Debby will be referring to quiet a few paragraph (P) numbers in the mid-latitude and tropical belt discussions below.

Debby has continued to defy westward-turning forecasts such as those from the National Hurricane Center and what I presented previously...tracking more northeastward than expected. This seems to suggest that the computer model runs that have wanted to take this northeast across north Florida and into the Atlantic (mainly the GFS model) were perhaps on to something.

Cut-off upper-level low (ULL) in the western Gulf of Mexico (paragraph P2) persists. Part of the reason I think this system tracked more northward than expected is attraction toward surface pressure falls caused by upper divergence between the NE edge of the ULL and warm core upper ridging (paragraph P7) covering the east half of this system. Also...the 1018 mb ridge mentioned in this special feature section yesterday is now hugging Debby from the northwest and preventing her from turning westward as remarked at the end of paragraph P1. Moreover...the open Atlantic ridge mentioned in paragraph P5 prevents Debby from going eastward. Therefore...Debby has had no choice but to continue northeastward toward the ridge weakness between the surface ridge mentioned in paragraph P1 and open Atlantic surface ridge in paragraph P5...the ridge weakness caused by various upper-level troughing and surface frontal systems mentioned in paragraph P2. The GFS model that has been insisting Debby will continue northeastward into the Atlantic suggests Debby will be deep-layered enough to "feel" the upper-level troughing in paragraph P2 indefinetly.

However...I am still skeptical of this. I don't think Debby will be deep-layered enough to "feel" the upper trough such that it goes into the Atlantic...instead getting influenced by the eastern nose of the surface to low-level ridge still progged to dive southeastward from western Canada as mentioned towards the end of paragraph P2. As Figure 1 below shows...I have Debby anticyclonically looping while beginning to become steered by this ridge...and then I have Debby continuing WNW thru day 5 while continuing to be steered by that ridge. If the west coast frontal system mentioned in paragraph P1 is deflected far north enough by the upper ridge mentioned in the same paragraph (as shown by models)...then the WNW track could be prolonged beyond day 5. My new track forecast is quiet to the right of the 1 PM CDT National Hurricane Center (NHC) forecast as shown in Figure 1.

The brand new 4 PM CDT NHC forecast (released after Figure 1 was created) shows a very slow northward track into the Florida panhandle thru 5 days...but I am still maintaining my track in Figure 1 which shows the anticyclonic loop offshore of the panhandle...followed by steady WNW track thru day 5.


Figure 1: My current 5-day Tropical Storm Debby forecast this afternoon.

Intensity-wise...not worrying about the dry air mentioned in paragraph P1...with the warm core upper ridge (paragraph P7) helping Debby's outflow. This extensive outflow is causing lift down below and over the ocean surface...allowing for moistening such that dry air is fought off. Debby has strengthened sooner than I thought despite westerly shear from cut-off west Gulf upper-level low (ULL) mentioned in paragraph P2. I take it then she has strengthened thanks to being centered below split flow upper divergence between the NE corner of the ULL and adjacent upper ridge in paragraph P7. I predict additional slow strengthening as we have seen...since the ULL is forecast by the models in the next 48 hours to retrograde westward and away while moving around the anticyclonic center of the upper ridge of paragraph P1. As the ULL departs...the westerly shear will lessen...allowing Debby's t-storms and warm core upper ridge/outflow (paragraph P7) to become more symmetrical and promote strengtening. Shear will remain low as the upper ridge in paragraph P1 passes north of Debby...but I expect weakening later on as the meandering forecast track shown in Figure 1 could allow Debby's prolonged winds to upwell cooler water beneath the northeastern Gulf of Mexico surface.

5-day forecast impacts in Figure 1 are what I think if Debby follows my forecast. Mention of isolated tornadoes is due to tornado warnings we have seen in south Florida since yesterday...but this is also a reminder that Debby could produce isolated tornadoes throughout the entire forecast period (as tropical cyclones are typically capable of). Impact swath is drawn based on the initial lopsided structure caused by westerly vertical shear from the west Gulf ULL...but then I make the impact swath more symmetric about the forecast storm track with the ULL expected to exit the picture. The impact swath barely includes the Florida Keys and south Florida...as the most recent radar images suggest that the bulk of south Florida rains may have ended indefinitely thanks to Debby's continued northeast track. With my meandering track shown in Figure 1...rainfall totals are likely to continue stacking up in Florida...and could later stack up in southern Georgia and SE Alabama...so watch out for possible major flooding. Not expecting as much in the way of rainfall totals in SW Alabama...Mississippi...and eventually Louisiana with a faster and more steady WNW track making the rainfall period not last as long in these areas.

...MID-LATITUDES DISCUSSION...
P1...Warm air advection ahead of surface frontal system hanging off west coast of North America continues supporting the upper ridge over the western US. Eastward progression of west coast surface system is currently blocked by strong surface ridge over western Canada mentioned in paragraph P2. Meanwhile...upper convergence on the east side of the west US upper ridge supports dry air and a surface 1019 to 1015 mb ridge hugging Tropical Storm Debby from the northwest...which is blocking Debby from being able to turn westward at this time.

P2...Frontal system and longwave upper trough over the eastern US is currently complicated. Surface front near the east coasts of the US and Canada persists...and all depressions along this front have consolidated to a 1007 mb center over Nova Scoatia whose local cool air advection has created a small upper vortex (see above birdseye charts). 1004 mb frontal cyclone diving SE from NW Canada is presently on the east coast of Hudson Bay...and its cool air advection has carved out a shortwave upper trough following behind. Yet another shortwave upper trough is seen over the Ohio Valley...which has formed between Tropical Storm Debby's warm core upper ridge and the upper ridge mentioned in paragraph P1. 24 hrs ago this longwave upper trough regime had left behind a cut-off upper vortex (interacting with Tropical Storm Debby) in the western Gulf of Mexico...and this cut-off feature still persists. Of final note...upper convergence on the back side of this longwave upper trough regime supports a strong west Canada surface ridge that is diving southeast.

P3...Upper ridge over the western Atlantic remains supported by warm air advection ahead of the complex frontal system outlined in paragraph P2 above. The south Greenland fragment of this upper ridge has re-merged with the main body of the upper ridge...and its eastern convergence supports 1020 mb surface ridging in the vicinity of south Greenland.

P4...Large upper vortex in the north-central Atlantic persists...and the surface frontal cyclone it supports has now whirled beneath the upper vortex center (effectively creating a deep-layered vortex). With a lack of divergence directly below the upper vortex...the surface cyclone will begin weakening. From the isobars drawn on the 1200Z TAFB analysis...the surface cyclone is currently below 1004 mb. Cut-off upper vortex SW of Bermuda in the previous discussion has been pushed eastward by Debby's sprawling warm core upper ridge...and is now due south of Bermuda.

P5...Open Atlantic surface ridge continues to have a 1028 mb center SE of the Azores that is supported with upper convergence NE of the E Atlantic upper ridge (paragraph P9) and W of the NE Atlantic upper trough (paragraph P6). This surface ridge also has a 1021 mb center north of the Lesser Antilles...which I surmise is supported by upper convergence as upper northerlies from Debby's sprawling outflow (paragraph P7) clashes with upper easterlies from upper vorticity mentioned in paragraph P8.

P6...Longwave upper trough in the NE Atlantic has moved into Europe...with the exception of a highly amplified cut-off fragment over the Canary Islands. The amplification of this cut-off fgrament is due to equal amplification of the east Atlantic upper ridge (paragraph P9) to its southwest. Divergence on the east side of this cut-off upper trough supports increased clouds on Morocco's coast.

...TROPICAL BELT DISCUSSION...
P7...Upper ridge over the southern Gulf of Mexico continues to sprawl with the support of Tropical Storm Debby's thunderstorm latent heat release. This upper ridge continues to support the upper outflow of Debby.

P8...Cut-off upper vorticity persists in a SW-NE elongation...from the eastern Caribbean to the tropical waters NE of the Lesser Antilles.

P9...Expansive east Atlantic upper ridge continues. In conjunction with the 1028 mb surface ridge mentioned in paragraph P5...deep-layered easterly flow exists south of this upper ridge such that dry air from the African desert is being advected westward across the Atlantic tropics (brown shading in the above thermo birdseye chart). A lobe of this upper ridge has amplified since the previous discussion thanks to warm air advection ahead of the deep-layered vortex mentioned in paragraph P4.

P10...Tropical wave WSW of the Cape Verde Islands in the previous discussion is now midway between the Cape Verdes and Lesser Antilles in this discussion. It remains suppressed by dry air mentioned in paragraph P9 above.

P11...Tropical wave that rolled off the west African coast yesterday is now south of the Cape Verde Islands. If the tropical wave in paragraph P10 is any indication...this tropical wave should also succumb to the dry air mentioned in paragraph P9.

Updated: 9:29 PM GMT on June 24, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #34

By: NCHurricane2009, 12:28 AM GMT on June 24, 2012

...JUNE 23 2012...8:40 PM EDT...
Tropical Storm Debby forms out of the Gulf of Mexico disturbance...becoming the earliest fourth tropical storm on record in the Atlantic basin. The previous holder of this record was Dennis in 2005...which was named on July 5 that year. See special feature section below for further details on Debby.

Elsewhere...it is quiet in the Atlantic tropics...

...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 anlaysis, 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 DEBBY...
Since the previous special feature discussion on this weather system...the surface low did initially regenerate southwestward toward the north Yucatan shore and beneath the favorable upper anticyclonic center of its warm core upper ridge. After that...I predicted previously it would track northwestward as the frontal system currently mentioned in paragraph P2 of the mid-latitudes discussion would influence the steering. Instead...it tracked more northward and took longer than I thought to become a tropical cyclone (but it is now Tropical Storm Debby). Part of my northwestward lean was associated with what I thought would be steering influence from what is now the 1018 mb ridge in the above birdseye charts (and mentioned in paragraph P1). A cut-off upper-level low (ULL) in the western Gulf of Mexico has spun up as the models have been predicting...see end of paragraph P2 for details. Part of the reason I think this system tracked more northward than expected is attraction toward surface pressure falls caused by upper divergence between the NE edge of the ULL and warm core upper ridging now covering the east half of this system.

Track-wise...the forecasts in Figure 1 from me and the National Hurricane Center (NHC) show a turn towards the west. This is similar to the forecast issued in my previous discussion...but located further north...which makes sense since the system tracked further north than expected as mentioned in the previous paragraph. Central North America surface ridge mentioned in the previous discussion that is expected to cause the westward turn has not yet entered the above birdseye charts...but is over western Canada while supported by upper convergence east of the upper ridge mentioned in paragraph P1 and west of the upper trough in paragraph P2. From western Canada...this surface ridge is acting to block the eastward progression of the west coast frontal system mentioned in paragraph P1. After the surface ridge dives southeast and steers Debby westward...the west coast frontal system will eventually move in and begin curving Debby's track more northward late in the forecast...which is what I hint at in Figure 1. Timing on when the track begins bending northward is based on surface map forecasts issued by the HPC on where the above weather features are expected to be.


Figure 1: My current Tropical Storm Debby forecast this early evening.

Intensity-wise...the first paragraph of this special feature section suggests favorable warm core upper ridging and outflow covering the east half of Debby...and this favorable outflow has a channel reaching into the cut-off upper low SW of Bermuda mentioned in paragraph P4. The west half of Debby meanwhile is inactive while battling westerly shear from the above-mentioned west Gulf upper-level low (ULL). This ULL is the only inhibiting factor for strengthening...so I keep Debby at 50 mph max winds through the first three days. After three days is when the models suggest the ULL will have retrograded westward out of the Gulf while influenced by the anticyclonic center of the upper ridge in paragraph P1. I expect Debby to be in favorable low shear south of this upper ridge...and with warm waters I expect Debby to be quickly developing more symmetrical thunderstorms and warm core upper outflow with the ULL out of the way. As a result...my forecast in Figure 1 shows brisk strengthening to a moderate category 1 hurricane as Debby approaches the upper Texas coast. My strengthening rate toward landfall is slowed as Debby gets more influenced by land.

Forecast impacts in Figure 1 are what I think if Debby follows my forecast. Mention of isolated tornadoes is due to a couple of tornado warnings we have seen in south Florida...but this is also a reminder that Debby could produce isolated tornadoes throughout the entire forecast period (as tropical cyclones are typically capable of). As the impact swath shows...initial storm structure is rather large and biased to the east of center thanks to aforementioned westerly vertical shear from the west Gulf ULL. My impact swath did not include the east coast of Florida...drawing it based on radar loops available by 6 PM CDT. As we have moved closer to 7 PM CDT...radar shows new heavy rain moving northward towards Miami...so perhaps rainfall impacts from Debby could encompass the east coast of Florida as well. Moving ahead...the impact swath becomes a bit smaller as I expect she will consolidate as she strengthens. I also make the impact swath more symmetric about the center with the reduction in shear expected as the unfavorable ULL exits the picture. At the very end...I bend the impact swath northward across east Texas/extreme west Louisiana as I believe the west coast frontal system will pull Debby's track more northward after landfall.

...MID-LATITUDES DISCUSSION...
P1...Warm air advection ahead of surface frontal system entering the western North American continent is supporting an upper ridge over the western US. Upper flow is heavily split between the anticyclonic center of this upper ridge (over SE Colorado) and mainstream upper westerlies flowing into the upper trough mentioned in paragraph P2 below. This split upper flow is supporting showers and t-storms over the north-central US. Otherwise...weather is quiet on the east side of this upper ridge...where upper convergence supports a surface 1018 mb ridge pushing into the east half of the US and Canada.

P2...Frontal cyclone (and associated supporting upper trough) that was centered over the central US/Canada border in the previous discussion has pulled NE across the Hudson Bay and has left the scope of the above birdseye charts. The upper trough is now over the eastern US...and the very long cold front tailing from this cyclone is along the east coasts of the US and Canada (where there are 1008 and 1009 mb frontal depressions). Another frontal cyclone from NW Canada is diving SE into the back side of this upper trough (marked with 1004 mb in the above charts)...and this upper trough has left behind a cut-off upper vortex in the west Gulf of Mexico interacting with Tropical Storm Debby (see special features section for further details). This cut-off's formation was driven by amplification of adjacent upper ridge mentioned in paragraph P1 above.

P3...Upper ridge over the eastern US has pushed eastward into the western Atlantic...but remains supported by warm air advection ahead of the complex frontal system outlined in paragraph P2 above. The south Greenland fragment of this upper ridge persists...and its eastern convergence supports a 1018 to 1019 mb surface ridge stretching southwestward across Newfoundland.

P4...Upper trough over the W Atlantic and Gulf of Mexico has undergone a few changes since the previous discussion. Its north end is now in the north-central Atlantic as a large upper vortex whose eastern peirpherial divergence has supported the rapid formation of what is now a 999 mb surface frontal cyclone which has absorbed the remnants of Chris. Of note...Chris did briefly become a hurricane...and cyclonically looped about this upper vortex as expected while closely following my projected track presented in the last discussion. However...Chris did not lose tropical characterisitcs or weaken as fast as I expected it too during the previous discussion. Cut-off upper vortex forming SW of Bermuda in the previous discussion persists. The Gulf portion of the upper trough has dissipated while becoming replaced with the warm core upper ridge associated with Tropical Storm Debby (see paragraph P7).

P5...Surface 1021 mb ridge over the open Atlantic has dissipated thanks to upper divergence ahead of north-central Atlantic upper vortex mentioned in paragraph P4. Surface ridge has re-located to the SE of the Azores...and strengthened to 1028 mb while taking advantage of upper convergence NE of the E Atlantic upper ridge (paragraph P9) and W of the NE Atlantic upper trough (paragraph P6).

P6...Longwave upper trough persists in the NE Atlanic. It has become amplified as the east Atlantic upper ridge (paragraph P9) has amplified to its southwest.

...TROPICAL BELT DISCUSSION...
P7...Upper ridge over the Caribbean has shifted to a location across the southern Gulf of Mexico while associated with the latent heat release of Tropical Storm Debby's thunderstorm clouds.

P8...Cut-off upper low (vorticity) east of the Lesser Antilles has become strecthed SW to NE thanks to the growth spurt of the upper ridge located northwest of this area and mentioned in paragraph P7 above. Its stretch now takes it from the eastern Caribbean to the tropical waters NE of the Lesser Antilles.

P9...Expansive east Atlantic upper ridge continues. In conjunction with the 1028 mb surface ridge mentioned in paragraph P5...deep-layered easterly flow exists south of this upper ridge such that dry air from the African desert is being advected westward across the Atlantic tropics (brown shading in the above thermo birdseye chart). This upper ridge has amplified since the previous discussion thanks to warm air advection ahead of 999 mb frontal cyclone mentioned in paragraph P4. Inverted upper trough that was embedded in this upper ridge is now making a WNW escape (as a very weak upper low) toward the upper vorticity mentioned in paragraph P8 above.

P10...Tropical wave that entered the eastern Caribbean in the previous discussion has been removed from TAFB analyses very early yesterday...as if it dissipated.

P11...Tropical wave south of the Cape Verde Islands in the previous discussion is now WSW of the islands in this discussion. It is suppressed by dry air mentioned in paragraph P9 above.

P12...Satellite imagery suggests the next tropical wave has rolled off the west coast of Africa...as marked in the lower-right corner of the above birdseye charts. If the tropical wave in paragraph P11 is any indication...this tropical wave should also succumb to the dry air mentioned in paragraph P9.

Updated: 1:51 AM GMT on June 24, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #33

By: NCHurricane2009, 11:20 AM GMT on June 21, 2012

...JUNE 21 2012...7:22 AM EDT...
Atlantic tropics are heating up. Chris strengthens to the southeast of Newfoundland using non-tropical processes...but still remains a tropical cyclone. Western Caribbean disturbance has moved into the Gulf of Mexico and is forecast to become the next tropical cyclone. See both special feature sections for further details.

Of note...if the Gulf of Mexico disturbance becomes a tropical storm...it will be the earliest fourth tropical storm on record in the Atlantic basin...beating Hurricane Dennis of 2005 which became a tropical storm on July 5.

Also watching disturbed weather south of Bermuda. See paragraph P3 in mid-latitudes discussion.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0132Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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 CHRIS...
As paragraphs P1 and P3 in the mid-latitudes discussion explains...the western Atlantic parent upper vorticity that helped to produce Chris has merged with an upper trough of the third North American frontal cyclone in recent days. The merger has recently developed an upper low to the SE of Newfoundland...thanks to a local maximum of cool air advection behind Chris's cyclonic circulation. In conjunction with a surface ridge to the NE (see end of paragraph P2)...this upper low is turning Chris northward and will eventually swing Chris in a counter-clockwise loop. The counter-clockwise loop turn forecast (Figure 1 below) is further complicated by the fact that the steering upper low will be pulled southward by continued cool air advection behind Chris's cylonic circuation. The further south the upper low becomes...the tighter the loop Chris makes. My forecast track in Figure 1 continues to follow the NHC forecast track (which has done very well in the last 24 hours)...but then I am to the right of the NHC forecast as Chris makes its loop. This is because I believe the upper low's position is too far NW to suggest that Chris will loop as tightly as the NHC forecast track currently shows.

Intensity-wise...Chris is a reminder that tropical cyclones that do not orginate from the deep tropics can have their entire vertical warm core circulation (surface spin and upper outflow) tucked below the 200 mb upper winds...which is why Chris is not getting sheared into oblivion desipte fast 200 mb winds out of the SW. Instead...it has strengthened while taking advantage of the divergent aspect of the 200 mb wind flow ahead of the western Atlantic upper vorticity (similar to how a non-tropical system strengthens). It has maintained a vertical warm core and impressive t-storms over Gulf Stream waters in the low 20s of deg C. The cold temps of the upper vorticity allow Chris to have instability and t-storms despite waters of below 26 deg C. Based on the eye feature (which has developed in the last 24 hours) becoming quiet impressive...I am forecasting 70 mph max winds by 11 AM this morning (higher than the NHC official forecast shows). I believe there is even a slight chance Chris is a brief hurricane by 11 AM.

Beyond that...Chris will soon cross the north wall of the Gulf stream...taking it to even cooler waters. I agree with the NHC forecast on when Chris becomes non-tropical (by loss its t-storms and vertical warm core when entering stable air over those cold waters). Non-tropical transition is forecast by 5 AM Friday (tomorrow) as shown in Figure 2.


Figure 1: Tropical Storm Chris Forecast

...SPECIAL FEATURE...GULF OF MEXICO DISTURBANCE...
Western Caribbean disturbance is pushing into the southeastern half of the Gulf of Mexico...and its warm core upper ridge has finally begun pushing out the shearing Gulf upper trough (paragraph P3 of mid-latitudes discussion). The very favorable anticyclonic center of the upper ridge is located just north of the Yucatan peninsula...and to the southwest of the disturbance's surface low pressure center. My forecast in Figure 2 below predicts TCF (tropical cyclone formation) beginning 24 hours from now while the surface center regenerates a bit southwestward beneath the favorable outflow of the upper anticyclonic center.

After TCF...the track philisophy in Figure 2 is initially northwest while the steering surface ridge offshore of North Carolina (mentioned in paragraph P2) gets knocked out by fourth frontal cyclone (mentioned in paragraph P1). The track bends back to the west toward the end of the forecast as a strong surface ridge over central North America develops behind the fourth frontal cyclone. Models still want to dump in a west Gulf of Mexico upper level low (ULL) by June 25...a cut-off feature from the upper trough associated with the fourth frontal cyclone. So I currently expect the forecast tropical cyclone to reach peak strength on June 24 before getting southwesterly and southerly shear on the east side of the ULL by June 25.

Some computer model runs still propose that the east side of this disturbance consolidates into another surface low by June 24 or 25 that tracks NE across Florida and then parallel to the east coast of the US . However...I believe the disturbance will have consolidated into a westard tracking tropical storm by then...the dominating surface low pressure field of the tropical storm prevnting another surface low from forming.


Figure 2: My current best guess forecast for the Gulf of Mexico disturbance this morning.

...MID-LATITUDES DISCUSSION...
P1...Third North American frontal cyclone in recent days has been moved to paragraph P3 below. Fourth such North American frontal cyclone (and associated supporting upper trough) is crossing the central US/Canada border with lowest presure of 1003 mb the above birdseye charts.

P2...Upper ridge over the eastern US remains amplified...thanks to warm air advection ahead of fourth frontal cyclone mentioned in paragraph P1. The upper ridge's eastern convergence continues to support a surface ridge. This surface ridge currently has a 1021 mb center offshore of North Carolina. The eastern Canada fragrment of this upper ridge is now over S Greenland. Eastern convergence from the S Greenland upper ridge supports a surface ridge located well NE of Tropical Storm Chris.

P3...Upper trough over the W Atlantic and Gulf of Mexico has merged with upper trough of third North American frontal cyclone mentioned in paragraph P1 above. At the north end of this merged upper trough...the third frontal cyclone is now over SE Canada with lowest pressure of 1003 mb. Further down the upper trough...Tropical Storm Chris is hooking northward on the trough's east side...and also has strengthened while taking advantage of divergence ahead of the upper trough (see 1st special feature section for details). As the upper ridge to the west (paragraph P2) remains amplified...a cut-off upper low along the upper trough is developing SW of Bermuda...and this upper low's eastern peripherial divergence supports a surface trough and t-storms south of Bermuda. Watching this area for any signs of development...especially since Chris somewhat suprised us by forming under similar circumstances just days ago. Finally...the Gulf portion of this upper trough remains split off...featuring a cut-off upper low at the TX/MX border and east-west fragment on the US Gulf coast.

P4...Surface 1027 mb ridge over the open Atlantic has weakened to 1021 mb in the last 24 hours...due to upper divergence ahead of upper trough in paragraph P3.

P5...Longwave upper trough persists in the NE Atlantic...with divergence ahead of this upper feature supporting a surface frontal activity from W Europe all the way towards Tropical Storm Chris. Divergence ahead of this NE Atlantic longwave upper trough continues to support a surface extratropical (non-tropical) low seen on satellite imagery SW of the British Isles.

...TROPICAL BELT DISCUSSION...
P6...Upper ridge over the Caribbean persists...enhanced by latent heat release of the t-storm clouds of the disturbance covered in the above 2nd special feature section. As the disturbance pushes into the Gulf of Mexico...the strongest portion of the upper ridge is shifting into the southern Gulf.

P7...Inverted upper trough E of the Lesser Antilles is now a cut-off upper low.

P8...Expansive east Atlantic upper ridge continues. In conjunction with the 1021 mb surface ridge mentioned in paragraph P4...deep-layered easterly flow exists south of this upper ridge such that dry air from the African desert is being advected westward across the Atlantic tropics (brown shading in the above thermo birdseye chart). This upper ridge seems remains concentrated into two areas...the western of which is associated with warm air advection ahead of the weather features in paragraph P3...the eastern of which is located toward Africa. Relatively new inverted upper trough profile (midway between the Lesser Antilles and Cape Verde Islands) shows up in between these two upper ridge areas.

P9...Vigorous tropical wave nearing the Lesser Antilles in the previous discussion has crossed those islands into the eastern Caribbean Sea. It is suppressed by dry air mentioned in paragraph P8 above.

P10...Tropical wave that rolled off of Africa yesterday is south of the Cape Verde Islands this early morning. It features a t-storm burst along the surface ITCZ. While it is in favorable low shear (thanks to deep-layered easterlies mentioned in paragraph P8)...it will likely struggle with expasnive dry air presently to the northwest (dry air also mentioned in paragraph P8).

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #32

By: NCHurricane2009, 9:55 AM GMT on June 20, 2012

...JUNE 20 2012...5:55 AM EDT...
Subtropical low Invest 95-L becomes Tropical Storm Chris in the northwest Atlantic...south of Newfoundland. See 1st special feature section for current details on this system.

Future of tropical disturbance in the western Caribbean Sea becoming uncertain as it pushes into the Gulf of Mexico. See 2nd special feature section for further details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1308Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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 CHRIS...
When we last talked about subtropical surface low Invest 95-L in the NW Atlantic (discussion #31)...it was back to a favorable (and less shearing) position with respect to its parent upper vortex...and was taking advantage of split flow upper divergence on the east periphery of said upper vortex. I had said there was a small chance of 95-L becoming a subtropical or tropical cyclone over Gulf Stream waters (albeit in the low 20s of deg C). Such tropical development over waters less than 26 deg C is possible as the parent upper vortex's cold temps can de-stabilize the atmosphere despite the mild waters. Indeed this happened yesterday afternoon...and we now have Tropical Storm Chris. According to the 1st NHC (National Hurricane Center) public advisory on this system...Chris is the 3rd earliest 3rd tropical storm in the Atlantic on record.

Computer models had been predicting an eastward turn along 40N latitude while rounding the north side of the subtropical ridge in paragraph P4...and indeed Chris started to follow this forecast. Then Chris started tracking ESE such that it became south of the computer model forecasts and first NHC track forecasts. When tropical cyclones develop from parent upper vortices (like Chris did)...they seem to be steered by their upper-level parent early on as the parent feature is deep-layered enough to do so. Chris's parent upper vortex recently merged with the tail end of a NE Atlantic upper trough (paragraph P5 in mid-latitudes discussion)...and I think Chris's early ESE track was caused by northwesterly flow on the back side of this upper-level merger.

Chris's early ESE motion has ended...now back on an east heading like it should have been. Upper trough of third Canadian frontal cyclone (paragraph P1) is digging into the parent upper vorticity over Chris. This...coupled with the amplifying upper ridge to Chris's west (paragraph P2)...is causing the upper vorticity over Chris to amplify...which should cause Chris to eventually turn north on the upper vorticity's east side as shown in Figure 1's forecast. Looking at current upper-level wind streamlines of the steering upper vorticity...the NHC track forecast basically follows...so I see no reason to disagree with it...especially as Chris is also following the NHC forecast track on satellite animations. Another sign that Chris will turn north is the blocking surface ridge of 1024 mb to the northeast (paragraph P2).

My intensity forecast in Figure 1 is a copy of the NHC's...as I also agree with it. Chris should hold its strength...then get stronger as it becomes non-tropical and takes advantage of upper divergence ahead of the upper vorticity that is steering it.


Figure 1: Tropical Storm Chris Forecast

...SPECIAL FEATURE...WEST CARIBBEAN DISTURBANCE...
Figure 2 below is my current best guess on how this system evolves over the next days. In the previous discussion...it was good to forecast an initial NW track instead of WNW as I was expecting a northward reformation toward the best-curved cloud bands (located toward Cuba...W Bahamas...south Florida). In fact...my forecast NW track was not north enough...so the current position of the disturbance (marked by surface trough in latest TAFB analyses) is a bit more NE of where I expected it to be by now. I maintain the NW track...then bend it northward and slow it by 0000Z June 22 as the steering surface ridge in paragraph P2 gets knocked out by fourth frontal cyclone mentioned in paragraph P1.

This disturbance is struggling to push out the Gulf of Mexico upper trough (paragraph P3) with its warm core upper ridge..and as a result it no longer appears it will develop by June 22. I hinted at the possibility of this disturbance struggling with the Gulf of Mexico upper trough in earlier discussion #30 paragraph P11.

After June 22...models show the upper winds remaining unfavorable...with upper westerly winds from the fourth frontal cyclone's upper trough (paragraph P1) shearing this system. I bend the track back westward by 0000Z June 24 as a strong surface ridge builds behind the fourth frontal cyclone. With the expected westerly shear...I keep the system a mere surface trough through this time.

After June 24...computer models still dump in a west Gulf of Mexico upper level low (ULL)...a cut-off feature from the upper trough that supports the fourth frontal cyclone. Currently...I project that the disturbance will regenerate slightly northeastward by 0000Z June 25 while taking advantage of upper divergence at the NE periphery of this ULL. The ULL could help reduce the westerly shear by this time...so I think there is a remote chance the disturbance becomes a weak tropical cyclone while steered westward on the north side of this ULL. Such a track would take this system into the Texas coast by 0000Z June 27...but this scenario is superficial at this time as no models show this happening...and moreover forecast skill that far out is difficult.

Some computer model runs propose that the east side of this disturbance consolidates into another surface low by June 24 that tracks NE across Florida and then parallel to the east coast of the US (also illustrated in Figure 2). This appears to be driven by upper divergence ahead of the upper trough associated with the fourth frontal cyclone in paragraph P1. While this surface low may be tropical early on...I think it is likely to become non-tropical quickly as such a development method is a non-tropical method.

Finally...computer models suggest some upper ridging to the south of the forecasted June 25 to 27 ULL (upper level low)...located over the Bay of Campeche. They hint at a tropical cyclone in the Bay of Campeche by that time while taking advantage of this upper ridging.

This is a highly uncertain situation with multiple scenarios possible...


Figure 2: My current best guess forecast for west Caribbean disturbance (emphasis on guess) this morning.

...MID-LATITUDES DISCUSSION...
P1...Third Canadian frontal cyclone in recent days (and its supporting upper trough) is now over the E coast of Hudson Bay with lowest surface pressure of 996 mb. As the associated upper trough continues east...it is expected to interact with Chris and transition him to non-tropical (extratropical) status (see 1st special feature section for more detials). Meanwhile...fourth frontal cyclone in recent days is entering the above birdseye charts from the western US (994 mb center in W Nebraska) with its supporting upper trough.

P2...Upper ridge over the eastern US has re-amplified as forecast...thanks to warm air advection ahead of fourth frontal cyclone mentioned in paragraph P1. The upper ridge's eastern convergence continues to support a surface ridge. This surface ridge currently has a 1022 mb center offshore of North Carolina and a 1023 mb center offshore of Massachusetts. A fragment of the upper ridge has split off into a shortwave upper ridge over E Canada associated with warm air advection ahead of the third cyclone mentioned in paragraph P1. Eastern convergence from this shortwave upper ridge supports 1024 mb surface ridge located well NE of Tropical Storm Chris.

P3...Upper trough over the W Atlantic and Gulf of Mexico persists. Peripherial upper diveregence on the east side of its upper vortex continues to support subtropical low Invest 95-L S of Newfoundland which has made the transition to Tropical Storm Chris (see 1st special feature section for further details). The Gulf portion of this upper trough remains split off...the split occuring as upper ridging from the latent heat release of the western Caribbean disturbance (2nd special feature above) expands.

P4...Surface 1027 mb ridge over the open Atlantic persists. From what I can gather from the latest 200 mb upper winds...it is supported as upper southerlies from E Atlantic upper ridge (paragraph P8) converges with upper westerlies from NE Atlantic upper trough (paragraph P5).

P5...Longwave upper trough persists in the NE Atlantic...with divergence ahead of this upper feature supporting a surface front stretching from the W Mediterranean all the way towards Tropical Storm Chris. 1018 mb frontal depression that was west of the Azores has moved across the Azores and is 1012 mb in the above birdseye charts. Divergence ahead of this NE Atlantic longwave upper trough also supports a relatively new extratropical (non-tropical) surface low seen on satellite imagery W of the British Isles...and it appears to have intensified quickly based on its satellite organization.

...TROPICAL BELT DISCUSSION...
P6...Upper ridge over the Caribbean persists...enhanced by latent heat release of the t-storm clouds of the west Caribbean disturbance covered in the above 2nd special feature section.

P7...Inverted upper trough E of the Lesser Antilles persists.

P8...Expansive east Atlantic upper ridge continues. In conjunction with the 1027 mb surface ridge mentioned in paragraph P4...deep-layered easterly flow exists south of this upper ridge such that dry air from the African desert is being advected westward across the Atlantic tropics (brown shading in the above thermo birdseye chart). In the midst of this dryness...there are batches of moisture from surface convergence/lift associated with the tropical waves in paragraphs P10 and P11. This upper ridge seems to have concentrated into two centers...the western of which is associated with warm air advection ahead of Chris's deep-layered cyclonic circulation...the eastern of which is located toward Africa. A new inverted upper trough profile (midway between the Lesser Antilles and Cape Verde Islands) shows up in between these two upper ridge centers.

P9...Tropical wave approaching the Lesser Antilles in the previous discussion has entered the eastern Caribbean Sea. It had been suppressed by the inverted upper trough in paragraph P7 and dry air advected westward from the African desert. This is likely the last discussion of this tropical wave as it has been removed from TAFB analyses this early morning. This is probably because the tropical wave has dissipated.

P10...Vigorous tropical wave midway between the Antilles and Cape Verde Islands in the previous discussion is now nearing the Lesser Antilles. It has generated some increased cloudiness with the help of enhanced poleward upper outflow...genearted by upper southerly winds on the west side of the upper ridge in paragraph P8.

P11...New tropical wave has rolled off the west coast of Africa. It features a t-storm burst along the surface ITCZ. While it is in favorable low shear (thanks to deep-layered easterlies mentioned in paragraph P8)...if the tropical wave in paragraph P10 is a good analogue...than we can too expect this tropical wave to struggle with dry air.

Updated: 6:59 AM GMT on June 21, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #31

By: NCHurricane2009, 11:24 AM GMT on June 19, 2012

...JUNE 19 2012...7:30 AM EDT...
Subtropical low that was over Bermuda in previous discussion #30 was upgraded to Invest 95-L during discussion #30A. See 1st special feature section for current details on this system.

Threat of emerging disturbance pulling NE out of the eastern Caribbean...as mentioned in special update #30A...has diminished.

Tropical disturbance has emerged in the western Caribbean Sea while heading toward the Bay of Campeche and southern Gulf of Mexico...a long-awaited event as computer models have been forecasting this scenario for several days. See 2nd special feature section for current details on this system.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1928Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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...SUBTROPICAL LOW INVEST 95-L...
After suprirising us with impacts over Bermuda during discussion #30...then getting better orgainzed through discussion #30A and throughout much of yesterday...the subtropical low suddenly lost t-storm activity last night when it became exposed to southwesterly shear on the SE side of its supporting upper vortex. The subtropical low is back to a favorable (and less shearing) position with respect to the upper vortex this morning...and is taking advantage of split flow upper divergence on the east periphery of said upper vortex. Some small pockets of t-storm clouds have even re-fired up on the north side of the subtropical low. The north and west sides of this system are more favored for firing t-storms...as this side is located closer to the warm Gulf stream waters.

Now what? As the computer model consensus has been showing...the NE track of the subtropical surface low is curving on a more eastward slant along 40N latitude while rounding the north side of the subtropical ridge in paragraph P4. This is taking it parallel to the Gulf stream...so I think this has a small chance to become a subtropical or tropical cyclone (or at least fire some last rounds of t-storm clouds) until it leaves the Gulf stream. Computer models suggest the eastward curving track of 95-L will soon be blocked as the 1025 mb ridge to the north of the system (paragraph P2) passes to the NE of the system. This will allow the third Canadian frontal cyclone and its supporting upper trough (paragraph P1) to catch up with 95-L as said frontal cyclone ejects eastward. Models seem to want to cyclonically loop the track of 95-L to the ESE of Newfoundland while it transitions to an intensifying non-tropical low supported by divergence of the frontal cyclone's upper trough. It is after this cyclonic loop that 95-L continues east. So even if this feature doesn't become a named storm or numbered depression...it looks to be around as a remnant non-tropical low for the next days.

...SPECIAL FEATURE...WEST CARIBBEAN DISTURBANCE...
See paragraph P6 in tropical belt discussion for how this system came together. This is something the models have been predicting for the last several days to develop into a tropical cyclone. And as we get closer to the expected timeframe of development...the way the models evolve the atmosphere is becoming increasingly complex...so the situation is not as clear cut as previously thought. So interests in the Gulf of Mexico should keep paying attention until it is clearer how this will evolve.

Figure 1 below is my current best guess on how this system evolves over the next days...after extensively studying computer model outputs of surface maps and upper wind maps. I initially take the system NW into the Yucatan...on a track further north than what the TAFB is suggesting (because the best-curved clouds are north of the TAFB central position of the surface low as if the surface low could regenerate northward). The NW track then bends north into the southern Gulf of Mexico as the steering surface ridge in paragraph P2 gets knocked out by fourth frontal cyclone mentioned in paragraph P1.

It is during the Yucatan timeframe that the models show the best upper wind conditions...with the system's warm core upper ridge having pushed out the Gulf of Mexico upper trough (paragraph P3)...and the warm core upper ridge merging with the east US upper ridge (paragraph P2) such that favorable upper outflow is tremendous. That is why I expect a tropical depression when it pulls north into the southern Gulf of Mexico.

Just as this system enters the Gulf...models show the upper winds become unfavorable...with westerly upper winds from the fourth frontal cyclone's upper trough shearing this system. The track bends west as a small low-level ridge passes by behind the fourth frontal cyclone...with a brief bend to the NW once again as a fifth frontal cyclone swings into the central US. In general...the fourth and fifth frontal cyclones merge in the computer models...and then a strong surface ridge builds behind them to steer this tropical cyclone westward toward the end of the Figure 1 forecast. My best guess (emphasis on guess) is a Texas/Mexico border landfall. Towards the end of the forecast...it seems the computer models dump in a west Gulf of Mexico upper level low (ULL)...a cut-off feature from the upper troughing that supports the fourth and fifth frontal cyclones. I expect this tropical cyclone to interact with the north and east sides of this ULL towards the end of the forecast. This interaction may lead to a more subtropical looking system at the end of the forecast (if it plays out this way).


Figure 1: My current best guess forecast for west Caribbean disturbance (emphasis on guess) this morning.

...MID-LATITUDES DISCUSSION...
P1...Second Canadian frontal cyclone in recent days and its supporting upper trough have swung northward across Hudson Bay and exited the picture. Third Canadian frontal cyclone and its supporting upper trough has swung into the picture from the upper-left...featuring a 999 mb surface center in the above birdseye charts. Unlike the previous two...this third cyclone is not expected to swing north across Hudson Bay. Instead...a fourth and strong Canadian frontal cyclone will enter the arena from the west...and warm air advection ahead of this fourth cyclone will re-amplify the east US upper ridge in paragraph P2 to the SW of the third cyclone. As the east US upper ridge re-amplifies...the ridge will push the supporting shortwave upper trough of this third cyclone more eastward such that the surface cyclone itself goes more east.

P2...Upper ridge over the eastern US is becoming squeezed out between upper troughs associated with the Canadian cyclones in paragraph P1...and the W Atlantic upper trough in paragraph P3. However...this upper ridge is expected to re-amplify thanks to warm air advection ahead of a fourth and strong Canadian cyclone expected to soon enter the picture. The upper ridge's eastern convergence continues to support a strong surface ridge. This strong surface ridge currently has a 1025 mb center offshore of Newfoundland and 1020 mb center over the SE US.

P3...Upper trough over the W Atlantic and Gulf of Mexico persists. Peripherial upper diveregence on the east side of its upper vortex continues to support subtropical low (special feature Invest 95-L) which has been tracking NNE across the NW Atlantic. The Gulf portion of this upper trough has recently split off into another upper low...the split occuring as upper ridging from the latent heat release of the western Caribbean disturbance (2nd special feature above) expands.


P4...Surface 1027 mb ridge center S of the Azores has shifted west. From what I can gather from the latest 200 mb upper winds...it is now supported as upper southerlies from E Atlantic upper ridge (paragraph P8) converges with upper westerlies from NE Atlantic upper trough (paragraph P5).

P5...Longwave upper trough persists in the NE Atlantic...with divergence ahead of this upper feature supporting a surface front stretching from W Europe to the Azores. Yeserday...this front was extended from the Azores into the NW Atlantic...perhaps to mark the divide between cooler air from the 1025 mb ridge in paragraph P2 and warmer air from the 1027 mb ridge in paragraph P4. The NW Atlantic portion of the front merged with subtropical low Invest 95-L...which is probably why the NHC gave it new fronts when it did not have any during the previous discussion #30 and #30A. As of this writing...the NE Atlantic longwave has two shortwave upper troughs...one supporting a 1018 mb frontal depression W of the Azores...the second supporting a 1000 mb frontal depression over Spain.

...TROPICAL BELT DISCUSSION...
P6...Upper ridge over the Caribbean persists. 1009 mb low (which had absorbed a tropical wave in previous discussion #30...paragraph P11) has moved NW into the west Caribbean and underneath this favorable upper ridge. See 2nd special features section above for further details on this developing situation.

P7...NE Caribbean upper trough has merged with the central Atlantic inverted upper trough (as expected during discussion #30 paragraph P10). The merger has an inverted signature E of the Lesser Antilles.

P8...In the east Atlantic...the upper ridge continues to expand rapidly...an effect due to relatively higher pressures south of the NE Atlantic upper trough mentioned in paragraph P5 above...and perhaps as the jet stream and its upper troughs have quickly relaxed their influence in this area.

P9...Tropical wave midway between the Cape Verdes and Lesser Antilles in the previous discussion has been steered rapidly westward toward the Antilles by deep-layered eastery flow S of the upper ridge in paragraph P8 and S of surface 1027 mb ridge in paragraph P4. Tropical wave remains suppressed by upper troughing mentioned in paragraph P7. The aformentioned easterly deep-layered flow may have caused the recent dry air outbreak stemming from Africa's desert seen by the brown shading in the above thermo chart. This tropical wave continues to also be suppressed in this dry air.

P10...Vigorous tropical wave S of the Cape Verde Islands in previous disuccsion has been steered very rapidly west by deep-layered easterly flow...S of the upper ridge in paragraph P8 and S of surface 1027 mb ridge in paragraph P4. It is now midway between the Antilles and Cape Verde Islands. As it remains in favorable low shear in this deep-layered easterly flow...and as the upper ridge helping to promote this low shear in paragraph P8 expands westward...it would seem conditions are favorable for development. However...the thermodynamics are not quiet that favorable...with the tropical wave mixed with dry air originating from Africa's desert.

Updated: 11:28 AM GMT on June 19, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #30A (Special Update)

By: NCHurricane2009, 5:37 AM GMT on June 18, 2012

...JUNE 18 2012...1:39 AM EDT...
This partial discussion is issued as a special update concerning the special feature of full discussion #30 which has recently become better organized NE of Bermuda...and has been upgraded to Invest 95-L by the Naval Research Laboratory (NRL) of the United States Navy. This special update is also issued for a possible tropical disturbance developing in the eastern Caribbean Sea. The possible disturbance in the eastern Caribbean should not be confused with the tropical system expected to reach the Bay of Campeche by June 20 (as discussed in paragraph P11 of discussion #30).

Figure 1 below is the lastest analysis of Invest 95-L. Unlike during full discussion #30 (special features section)...the most recent ASCAT pass cyclonic surface winds now matches the position of the LLC (low-level center) seen on satellite imagery. Despite tracking NE toward increasingly cooler waters...the blue arrows drawn in Figure 1 below suggests upper divergence at the NE periphery of the upper vortex that has allowed t-storm activity to intensify on the west side of the LLC. The east side of the LLC remains covered in a dry slot which was discussed in full discussion #30 (special feature section). Given the better defined LLC and increase in t-storms...I think the chances for this to become a subtropical or tropical cyclone in the next 24 hours has gone up. Beyond 24 hours...its NE track will take it to even cooler waters less favored for development.


Figure 1: Latest analysis of Invest 95-L...formerly subtropical low that passed over Bermuda. Upper divergence illustrated with blue arrows is supporting the low pressure LLC at the surface.

In full discussion #30...paragraph P8...it was mentioned that the strongest storm activity in the Caribbean Sea was located towards Jamaica..E Cuba...Hispaniola...and Puerto Rico...where northerlies across the Caribbean upper ridge heavily diverged with westerlies from the upper trough/vortex associated with what is now Invest 95-L. The storm activity near Hispaniola and Puerto Rico has been so strong that latent heat release from the clouds has flared up a new upper ridge as illustrated in Figure 2 below. This new upper ridge is also being supported by warm air advection ahead of Invest 95-L's broad cyclonic flow as shown in Figure 2. This upper ridge has relaxed the westerly vertical shear over the area...and could be supportive for a new surface low to develop and track NE out of the Caribbean as illustrated in Figure 2. Of final note...a computer model scenario was briefly mentioned in old discussion #26 paragraph P6 where a tropical/subtropical cyclone would track NE out the Caribbean from June 18 to 20. This potential disturbance in the eastern Caribbean fits this scenario much better than Invest 95-L does.


Figure 2: Possible Disturbance emerging from the eastern Caribbean Sea. Watch out for heavy rains in Puerto Rico and Hispaniola (Haiti and the Dominican Republic) as this possible disturbance tracks NE out of the Caribbean. The NE track would be supported by flow between Invest 95-L to the northwest and 1027 mb ridge south of the Azores (Azores ridge mentioned in previous discussion #30...paragraph P6).

Updated: 6:09 AM GMT on June 18, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #30

By: NCHurricane2009, 12:30 AM GMT on June 18, 2012

...JUNE 17 2012...8:35 PM EDT...
Bermuda impacted by storm with characteristics of a subtropical cyclone. However...because the low-level center (LLC) was not well-defined...it did not meet the meteorological criteria to be a named storm or numbered depression. See special feature section for further details.

Still watching for threat of tropical cyclone formation beginning June 20 in the Bay of Campeche and western Gulf of Mexico region...although I am becoming increasingly skeptical of how favorable the upper winds will be to allow this. See paragraph P11 for further details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1335Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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...BERMUDA SUBTROPICAL LOW...
See paragraph P3 in the mid-latitudes discussion for how this subtropical surface low developed. If we had paid closer attention to the computer model scenario briefly mentioned in previous discussion #26 (towards the end of paragraph P6)...we may have caught and better forewarned this scenario. Disucssion #26 paragraph P6 had briefly mentioned a cut-off upper vortex with surface subtropical-to-tropical development off the SE US by June 18. Indeed...we have a cut-off upper vortex in this region and located W of Bermuda...whose NE peripheral upper divergence triggered surface subtropical development over Bermuda as explained in paragraph P3 of today's mid-latitudes discussion.

Here is a timeline of the situation that rapidly developed over Bermuda today:

(a) By 1200Z...the NHC TAFB analysis shows the surface subtropical low as an elongated feature with a 1010 mb center over the island and 1014 mb center ENE of the island...as shown in the above birdseye charts as well.

(b) Shortly thereafter...radar imagery from the Bermuda Weather Service (Figure 1a) shows a well-defined low-level circulation (LLC) very close to the island. Correspondingly...observations from Hamilton International Airport (Figure 2) shows a rapid pressure drop to 1006 mb as if the central pressure is lower than the 1200Z TAFB analysis. Sustained winds rise to just below tropical storm force...with gusts well into tropical storm force...as the tight LLC in Figure 1a passes over. The rise in winds is possibly due to the tight pressure gradient of the small-sized LLC.

(c) Not long after...the tight LLC in Figure 1a is just east of Bermuda by Figure 1b...but is becoming absorbed into a much larger and broader LLC well east of Bermuda. Because the newer and broader LLC in Figure 1b does not have a sharply defined swirl in visible sat imagery...and because there is no steady LLC location (radar images in Figures 1a and 1b are less than an hour apart)...it appears this system is elongated SW-NE at the surface with multiple LLCs possible. Without a single well-defined LLC...this system cannot be upgraded to a named storm or numbered depression despite the observed impacts to Bermuda.

(d) By 2000Z...we still struggle to find a well-defined LLC. The best guess of an LLC based on satellite organization is marked in Figure 1c...while the 2000Z ASCAT pass shows the nearest LLC signature to the east of the satellite fix! The nearest ASCAT LLC signature also shows an SW-NE elongated LLC.

(e) Newer 1800Z TAFB analysis from the NHC shows the low down at 1005 mb...which better matches the pressure observations from Bermuda.


Figure 1: (a) and (b) are radar images from the Bermuda Weather Service. (c) is an ASCAT pass in the vicinity of the surface subtropical low that shows satellite-calculated surface wind speed and direction. BLT means Bermuda Local Time...Z means Zulu time.


Figure 2: Screenshot of surface observations at Bermuda's Hamilton International Airport for June 17, 2012. Notice the most significant winds and pressure drops occur during the passage of the LLC signature shown in Figure 1a.

Looking ahead...the most recent observations in Figure 2 show improving weather conditions for Bermuda (slower winds...no rain) as this subtropical surface low pressure system departs to the NE. The end in rainfall is due to Bermuda becoming caught in the system's dry slot. The dry slot is caused by the circulation swallowing dry...sinking air from the adjacent eastern convergence of the upper ridge in paragraph P2 below. Without a well-defined LLC in ASCAT passes or satellite imagery...with dry air ingestion...and with the system tracking NE toward cooler water...I do not expect this to ever be a named or numbered subtropical cyclone. Prognosis is to keep watching sat imagery and ASCAT passes...and if it shows signs of becoming a better-organized subtropical cyclone...I will write a special update.

...MID-LATITUDES DISCUSSION...
P1...First Canadian frontal cyclone (over Hudson Bay) and it supporting upper trough have fizzled. Second Canadian frontal cyclone and its supporting upper trough are showing towards the upper-left of the above birdseye charts. Its surface 995 mb center (located over south-central Canada) has whirled beneath its upper trough such that it is currently deep-layered. Third Canadian frontal cyclone (located over SW Canada) is about to enter the above birdseye charts from the upper-left. A fourth Canadian frontal cyclone will enter the arena by June 20.

P2...Upper ridge over the eastern US has recently further amplified ahead of second Canadian frontal cyclone mentioned in paragraph P1...and is expected to be amplified for a few more days as the third and fourth Canadian frontal cyclones supply supportive warm air advection ahead of themselves. The upper ridge's eastern convergence continues to support a strong surface ridge. This strong surface ridge currently has a 1027 mb center offshore of Newfoundland and 1023 mb center over the SE US.

P3...Upper trough over the W Atlantic and Gulf of Mexico persists. Due to the amplification of upper ridge in paragraph P2 above...its Gulf portion is pushed further south...and the Atlantic portion has amplified to the degree that it now has a cut-off upper vortex W of Bermuda. N Gulf of Mexico surface trough once supported by this upper trough's divergence is just offshore of Louisiana while bringing some scattered showers/t-storms to the area. Divergence maximum on the NE corner of upper vortex W of Bermuda has caused the surface 1009 mb low near Bermuda to intensify into a subtropical surface low over the island in the last 24 hours. In the above birdseye charts...it is a fairly elongated feature marked with a 1010 mb center over Bermuda and 1014 mb center well ENE of Bermuda. See above special feature section for more details on this elongated subtropical surface low.

P4...Upper trough in Greenland's vicinity has been absorbed into NE Atlantic upper trough mentioned in paragraph P7 below.

P5...Upper vortex in NW Atlantic has been absorbed into upper trough mentioned above in paragraph P3.

P6...Surface 1027 mb ridge center S of the Azores persists. From what I can gather from the latest 200 mb upper winds...it is now supported as upper southerlies from E Atlantic upper ridge (paragraph P10) converges with upper westerlies from NE Atlantic upper trough (paragraph P7).

P7...Upper trough persists in the NE Atlantic...with divergence ahead of the trough supporting a surface front stretching from W Europe to the Azores. Briefly during 1200Z TAFB and 1335Z HPC analyses...this front was extended from the Azores into the NW Atlantic...perhaps to mark the divide between cooler air from the 1027 mb ridge in paragraph P2 and warmer air from the 1027 mb ridge in paragraph P6. Along this front's extension...a weak surface low was seen spinning on visible satellite to the ESE of Newfoundland.

...TROPICAL BELT DISCUSSION...
P8...Upper ridge over W half of the Caribbean persists. Various cloud cover and t-storm activity induced by the outflow of this upper ridge persists across the Bay of Campeche...SE Mexico...Caribbean...and Central America. The strongest of this activity (towards Jamaica..E Cuba...Hispaniola...and Puerto Rico) is located where northerlies across this upper ridge heavily diverge with westerlies from the paragraph P3 upper trough. A surface trough has become associated with this upper divergence and heavy activity...which is a southward extension of the Bermuda subtropical surface low mentioned in paragraph P3 and today's special feature section.

P9...NE Caribbean upper trough has shifted east to the waters E of the Lesser Antilles.

P10...Upper vorticity in E tropical Atlantic has now concentrated into an inverted upper trough in the central tropical Atlantic...and could very well merge with upper trough in paragraph P9 above. In the far east Atlantic towards the W coast of Africa...an upper ridge is expanding...an effect due to relatively higher pressures south of the NE Atlantic upper trough mentioned in paragraph P7 above.

P11...24 hrs ago...a tropical wave was marching across the east Caribbean...and t-storms flared up in the Colombia-Panama area...triggered by split upper flow (between easterlies SE of the W Caribbean upper ridge of paragraph P8...and westerlies SW of the paragraph P9 upper trough). The split upper flow triggered a new 1009 mb surface low in the last 24 hours..and the aforementioned tropical wave has merged with it. Paying attention to this 1009 mb low as it appears this is what the models have been spinning up into a Bay of Campeche tropical cyclone around June 20. Challenges this system faces along the way will be land interaction with Central America/SE Mexico and vertical shear by the Gulf of Mexico upper trough (paragraph P3 above). I have become skeptical of tropical cyclone development as the Gulf upper trough shifted south (see paragraph P3 for why this south shift occurred)...which has increased unfavorable northwesterly vertical shear where this tropical cyclone is supposed to spin up. However...models still insist that the disturbance's latent heat release will feed the W Caribbean upper ridge such that the upper ridge expands and pushes out the shearing Gulf of Mexico upper trough. Where this possible tropical cyclone ends up tracking depends on the strength of the eventual fourth frontal cyclone mentioned in paragraph P1. A stronger fourth frontal cyclone will pull the tropical cyclone more northward toward it...and vice versa for a weaker frontal cyclone. Looking at the GFS trends...each run suggests a weaker and more north fourth frontal cyclone...which leans toward a S Texas/NE Mexico tropical cyclone landfall rather than an E Texas coast tropical cyclone landfall.

P12...Tropical wave WSW of the Cape Verde Islands in the previous discussion is now midway between the Cape Verdes and Lesser Antilles. It remains suppressed in a dry air mass (shown in today's thermodynamics chart)...and animation of the last days worth of thermo charts suggests this dry air orignated from Africa's desert. Tropical wave also remains suppressed by upper vorticity mentioned in paragraph P10.

P13...Satellite animation suggests the most impressive tropical wave of the season thus far has rolled off the W coast of Africa...and I have marked it to be south of the Cape Verde Islands at 1200Z (even though TAFB has not marked it in their 1200Z analysis). It is in a favorable upper outflow environment beneath the upper ridge in the far east Atlantic...mentioned in paragraph P10 above. Concerning its favorability for development...Will be watching to see if said upper ridge stays with this tropical wave...or if the tropical wave leaves the upper ridge and moves into less favorable upper winds beneath the upper vorticity in paragraph P10 above.

Updated: 3:38 AM GMT on June 18, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #29

By: NCHurricane2009, 7:01 PM GMT on June 16, 2012

...JUNE 16 2012...3:05 PM EDT...
Last chance for a June tropical cyclone in the Atlantic beginning June 20. Interests in the Bay of Campeche and western Gulf of Mexico region should monitor this situation carefully. See paragraph P11 below for further details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1327Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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...Frontal cyclone from SW Canada and it supporting upper trough have continued east into the Hudson Bay region since the previous discussion. Warm air advection ahead of this frontal cyclone generated a new shortwave upper ridge over the W Great Lakes that has since undergone a tremendous growth across the eastern US...in part due to latent heat release from the central US severe t-storm clouds this frontal cyclone was producing in the previous discussion. This was just the first of a few surface cyclones/shortwave upper troughs that will swing in from SW Canada thru this week...in fact a second is already entering the arena from the upper-left of the above charts and producing another round of central US severe t-storms. Numerical models show a third and even a fourth system swinging in thru June 20.

P2...Upper ridge over the eastern US (mentioned in paragraph P1 above) continues its sprawl...and shows no signs of decaying with ample warm air advection/severe t-storm latent heat release to be expected ahead of all surface cyclones mentioned in paragraph P1. It has absorbed the W Atlantic upper ridge (in paragraph P3 of the previous discussion)...and its eastern convergence has taken over support of all strong surface ridges mentioned in paragraph P3 of the previous discussion. This strong surface ridge currently has a 1034 mb center on the E coast of Canada and 1028 mb center on the NE US coast.

P3...Shortwave upper trough has moved from the SE US into the W Atlantic and Gulf of Mexico...becoming pushed southeastward by sprawling upper ridge in paragraph P2 above. 1014 mb AL/GA border low supported by divergence ahead of this upper trough has moved southwestward into the NE Gulf of Mexico (as a surface trough) while steered by strong surface ridge mentioned in paragraph P2 above...and expect it to continue W across the N Gulf of Mexico while steered by this surface ridge. Yesterday afternoon...this surface trough had a t-storm blow up and was briefly mentioned in the NHC Tropical Weather Outlook...but to no avail as the surface trough was under immense westerly vertical shear S of the upper trough. Surface trough again having a t-storm blow up this afternoon...this time while beneath lower shear directly under the upper trough axis (and perhaps triggered by instability from the cold temps of upper trough axis). I am cautious to sugggest tropical cyclone formation from this surface trough as it is directly below the upper trough. If the t-storm latent heat release shows signs of locally punching out the upper trough...then I will write a special update for possible tropical development (otherwise I don't think it will develop). Finally...1010 mb frontal low SE of Virginia also supported by divergence ahead of this upper trough...and has moved SE toward Bermuda (and now is 1009 mb) while steered in NW flow between surface ridge in paragraph P2 above and dissipating surface low mentioned in paragraph P5 below.

P4...Upper trough over E Canada and 1010 mb surface low it is supporting have moved offshore into the Atlantic high seas in Greenland's vicinity. Surface low has weakened to 1018 mb and is over the S tip of Greenland.

P5...Upper vortex in NW Atlantic persists...but the surface low below is not. The surface low has either dissipated or become absorbed by tail end of cold front mentioned in paragraph P7 below.

P6...Upper-levels of deep-layered anticyclone S of the Azores has dissipated...becoming replaced by the upper trough mentioned in paragraph P7 below. What is left is a surface 1027 mb ridge center at this hour...midway between the Azores and Canary Islands.

P7...Upper trough persists in the NE Atlantic...supported by cold air advection behind the strong surface cyclone it manifested with divergence ahead of itself. This surface extratropical (non-tropical) cyclone has moved into the British Isles per latest satellite imagery. Cold front tailing from this surface cyclone has pushed southward into the Azores...where a new 1018 mb frontal depression has formed thanks to upper divergence ahead of the upper trough.

...TROPICAL BELT DISCUSSION...
P8...Eastern Pacific Hurricane Carlotta and its associated warm core upper anticyclone made landfall in SE Mexico last night...now weakened to a tropical depression due to the landfall. Its warm core upper anticyclone has merged with Panama upper anticyclone to create a singular upper ridge that covers the W half of the Caribbean. Surface tropical wave that was getting sheared on the north side of this upper ridge has been absorbed by the surface low pressure field of Carlotta. Various cloud cover and t-storm activity induced by the outflow of this upper ridge exists across the Bay of Campeche...SE Mexico...W Caribbean...and Central America.

P9...NE Caribbean upper trough from previous discussion persists.

P10...Upper vortex in E tropical Atlantic is breaking up into smaller vortices retrograding westward. In the far east Atlantic towards the W coast of Africa...an upper ridge is redeveloping...an effect due to relatively higher pressures south of the NE Atlantic upper trough mentioned in paragraph P7 above.

P11...Tropical wave approaching the Lesser Antilles in the previous discussion has now crossed the islands into the eastern Caribbean. While crossing the islands...it had produced enhanced weather while interacting with divergence ahead of upper trough in paragraph P9 above...but now is inactive while suppressed beneath this upper trough. Ahead of this tropical wave...t-storms have flared up in the Colombia-Panama area...triggered by split upper flow (between easterlies SE of the W Caribbean upper ridge of paragraph P8...and westerlies SW of the paragraph P9 upper trough). Tonight into tomorrow...this tropical wave will move into this split upper flow and t-storms...and it will be interesting to see if a tropical disturbance gets going as the tropical wave's surface convergence further enhances the agitated weather. If so...I will be upgrading this to a special feature as it appears this is what the computer models have been developing into a Bay of Campeche tropical cyclone around June 20. Challenges this system faces along the way will be land interaction with Central America/SE Mexico and westerly vertical shear by the Gulf of Mexico upper trough (paragraph P3 above). However...models suggest that the disturbance's latent heat release will feed the W Caribbean upper ridge such that the upper ridge's outflow sustains the disturbance...and moreover the upper ridge pushes out the shearing Gulf of Mexico upper trough. What is disconcerting is that models do merge the W Caribbean upper ridge with the east US upper ridge (in paragraph P2 above). If this happened....the upper anticyclonic outflow would be tremendous...which would support a strong tropical cyclone out of this. The eventual fourth frontal cyclone in paragraph P1 above would pull this tropical cyclone northward from the Bay of Campeche...but it is unclear if the cyclone will make landfall on the E Texas coast...or instead turn westward into the S Texas coast or NE Mexico by a ridge that builds behind this fourth cyclone.

P12...Tropical wave S of the Cape Verde Islands in the previous discussion is now WSW of the islands...and remains suppressed beneath the upper vorticity mentioned in paragraph P10.

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #28

By: NCHurricane2009, 4:15 AM GMT on June 15, 2012

...JUNE 15 2012...12:20 AM EDT...
As far as tropical cyclone activity is concerned...all clear in the Atlantic tonight.

...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 anlaysis, 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 indicating surface lows, Hs indicating 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...Frontal cyclone from SW Canada continues east...and associated upper trough is moving across the western US tonight. Warm air advection ahead of this frontal system has generate a new shortwave upper ridge over the W Great Lakes. Cold front extending from SW Canada cyclone is pushing across the central US with associated severe t-storms.

P2...Shortwave upper trough has moved from the central US into the SE US in the last 24 hours. Divergence ahead of this upper trough now supports a 1014 mb frontal low over the AL/GA border...and a 1010 mb frontal low SE of Virginia...both frontal features left behind by old Hudson Bay system as mentioned in paragraph P3 below.

P3...Surface frontal cyclone that was over Canada's Hudson Bay has left behind several features. In the upper-levels...an upper trough is over E Canada (once caused by the cyclone's cold air advection) and upper ridge is over the W Atlantic (once caused by the cyclone's warm air advection). Convergence behind the E Canada upper trough supports 1030 mb center below and a 1028 mb center exiting Michigan. Convergence ahead of W Atlantic upper ridge supports 1030 mb center S of Greenland. Finally...this Hudson Bay cyclone had left behind a decaying front with a 1006 mb low over E Canada and 1009 mb low offshore of Virginia. The 1006 mb low is now 1010 mb but supported by divergence ahead of E Canada upper trough. The 1009 mb low offshore of Virginia is now 1010 mb...and the decaying front has yet another low of 1014 mb at the AL/GA border. Both the 1010 and 1014 mb lows are now associated with upper trough mentioned in paragraph P2 above.

P4...Upper vortex in NW Atlantic persists...and remains nearly stacked with 1009 mb low in the above charts. The Bahamas surface trough left behind by this system has been cancelled in NHC TAFB analyses...and the associated leftover clouds are pulling NE away from the Bahamas while associated with divergence on the back side of W Atlantic upper ridge (mentioned in paragraph P3 above). I stopped considering the 1009 mb surface low a threat for subtropical cyclone development in my previous discussion. However...it is interesting to note that the NHC dropped all fronts attached to the 1009 mb low in the recent 1800Z TAFB analysis as if it is less non-tropical. I still do not expect subtropical development as the convective cloudiness refuses to improve...and the thermodynamic picture gets less favorable with time as the 1009 mb low is forecast to track ENE toward even cooler waters.

P5...Deep-layered anticyclone S of the Azores has vertically de-coupled...with the upper anticyclonic center moving ENE while becoming associated with warm air advection ahead of system in paragraph P6 below. Surface 1026 mb center S of the Azores remains at this location and has weakened to 1025 mb in the last 24 hours.

P6...Relatively new upper trough persists in the NE Atlantic...supported by cold air advection behind the strengthening surface cyclone it has manifested with divergence E of the upper trough axis. This surface extratropical (non-tropical) low is not in the scope of TAFB nor HPC analyses...so I am using satellite imagery to fix the position of this low in the above charts. This surface low is moving into W Europe...and appears vigorous based on its satellite organization.

...TROPICAL BELT DISCUSSION...
P7...Upper trough in the Gulf of Mexico is absorbed by upper trough mentioned in paragraph P2 above.

P8...I forecasted in discussion #27 pargraph P10 that the Panama upper anticyclone (in the Caribbean) would shift west over the building latent heat release of eastern Pacific TD 3-E (which is now TS Carlotta)...and in turn shearing upper northwesterlies would spread across the Caribbean in the wake of the exiting upper anticyclone. Instead...Carlotta has built a seperate upper anticyclone overhead while the Panama upper anticyclone has remained stationary...and a new Yucatan upper trough has formed between the two upper anticyclones. Despite this deviation from my forecast...vast shearing upper westerlies still have developed outside of these upper anticyclones...and the Caribbean Sea tropical wave following behind Carlotta stands no chance of developing beneath this shear. This could be a particularly dangerous situation for the S coast of Mexico as E-Pac TS Carlotta continues to strengthen beneath its upper anticyclone...and get steered NW toward the area by the Panama upper anticyclone. As Carlotta and its upper anticyclone shift northward & closer to the Atlantic side of things...computer models still want to take advantage by expanding said upper anticyclone and develop a tropical cyclone below it in the Bay of Campeche beginning June 20. As we get closer to the June 20 timeframe thru this week...it will become clearer exactly how (or even if) this situation plays out.

P9...In discussion #27 paragraph P10...a new central Caribbean upper trough was briefly mentioned...which developed in the wake of the upper anticyclones discussed in paragraph P8 above. This upper trough has shifted ENE into the NE Caribbean while gravitated toward the upper vortex mentioned in paragraph P4 above.

P10...Upper ridge in E tropical Atlantic has finished reversing into an upper vortex. This reversing occurred as the upper-levels of anticyclone to the north (in paragraph P5) gained strength from warm air advection. The upper vorticity midway between the Lesser Antilles and Azores (discussion #27 paragraph P8) has been absorbed into this new E Atlantic upper vortex.

P11...Upper ridging persists south of the paragraph P4 1009 mb deep-layered cyclone (where upper-level pressures are relatively higher)...located across the E Caribbean and central tropical Atlantic.

P12...Tropical wave continues approaching the Lesser Antilles tonight...but is under a hostile westerly shear enivronment on the north side of the upper ridge mentioned in paragraph P11 above. Cloud cover already exists over the Lesser Antilles and ahead of this tropical wave...thanks to upper divergence ahead of upper trough in paragraph P9. As the tropical wave interacts with this upper divergence...weather activity over the Lesser Antilles is bound to increase.

P13...Tropical wave that emerged western Africa last evening is S of the Cape Verde Islands tonight. Since the E Atlantic is now covered by an upper vortex (as explained in paragraph P10 above)...upper winds will be unfavorable for this tropical wave to develop.

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #27

By: NCHurricane2009, 5:21 AM GMT on June 14, 2012

...JUNE 14 2012...1:30 AM EDT...
Deep-layered low in NW Atlantic not expected to become subtropical. While Caribbean Sea activity remains on the upswing...the eastern Pacific side of the activity is more favored. See paragraphs P4...P9...and P10 for further details on these situations.

...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 anlaysis, 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 indicating surface lows, Hs indicating 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 frontal cyclone in the mid-latitudes is entering from the upper-left corner of the above charts...from SW Canada.

P2...A low-amplitude shortwave upper trough has also centered entered the arena...currently marked over the central US in the above charts.

P3...Surface frontal cyclone over Canada's Hudson Bay has exited the scope of above charts while moving northward beneath its parent upper trough. A long frontal boundary is left behind by this cyclone...which features a 1006 mb low in E Canada and 1009 mb low offshore of Virginia. Convergence behind this parent upper trough supports a 1018 mb ridge on the Louisiana Gulf coast and 1026 mb ridge over Michigan. Warm air advection ahead of this weather system supports upper ridge which has recently moved offshore into the W Atlantic. Convergence E of this upper ridge axis supports a surface 1030 mb center over S Greenland...and 1020 mb offshore of Newfoundland.

P4...Upper vortex in NW Atlantic persists...and remains stacked above 1010 mb frontal low which is now 1009 mb in the above charts. Accelerational divergence SE of this upper vortex had supported a bare surface front across the central Atlantic over the last 48 hours...but now what is left of this front is a surface trough over the Bahamas and another surface trough about to get absorbed by front attached to 1009 mb low. The Bahamas surface trough almost appears to be merged with the N end of Caribbean Sea tropical wave (mentioned in paragraph P9 below). The Bahamas surface trough has also obtained some t-storm activity with the help of upper outflow from the upper ridge axis mentioned towards the end of paragraph P3 above. With this upper ridge expected to become squeezed out between upper trough in paragraph P3 and upper vortex mentioned in this paragraph...the Bahamas surface trough will lose this favorable environment. The 1009 mb frontal low below the upper vortex continues firing convective cloudiness...perhaps as the upper vortex is cold enough to de-stabilize the atmosphere despite waters of 23 deg C. However...this convective activity has not been strong enough nor close enough to the 1009 mb center for subtropical cyclone development...and the thermodynamic picture is not going to get any better for development (with the cold temp of upper vortex at its pinnacle and sea surface temps not getting any warmer along the 1009 mb center's track). After this assessment...I believe this system has no chance to become a subtropical cyclone.

P5...Deep-layered anticyclone S of the Azores persists...with the surface center now weaker at 1026 mb.

P6...New upper trough has developed in the NE Atlantic...in relatively low pressures between upper anticyclone in paragraph P5 above and upper ridge axis mentioned towards the end of paragraph P3. Satellite animation reveals a sizeable cloud mass and spin heading toward western Europe...which I beleive is a new surface low supported by divergence ahead of this NE Atlantic upper trough.

...TROPICAL BELT DISCUSSION...
P7...Upper trough persists across the Gulf of Mexico tonight.

P8...East-west upper trough has dissipiated in the Caribbean Sea. Upper vorticity midway between the Lesser Antilles and Azores persists.

P9...Upper anticyclone over Cuba has been absorbed by upper ridge axis mentioned toward the end of paragraph P3. 48 hours ago...upper anticyclone toward Panama started enhancing t-storms over the surface ITCZ (discussion #25 paragraph P7). Looking at Hovmoller Diagrams on the NHC webpage...a chunk of this t-storm activity pushed into the eastern Pacific...strengthened beneath high divergence on the SW edge of the Panama upper anticyclone...and now we have tropical depression 3-E in the eastern Pacific tonight. To the east of TD 3-E...tropical wave continues marching west across the Caribbean while enhancing t-storm activity beneath the Panama upper anticyclone and over Central America. Panama upper anticyclone has grown in size while inflated by latent heat release of the tropical wave and TD 3-E t-storms....and in turn the upper anticyclone is aiding the outflow to sustain TD 3-E and the tropical wave.

P10...Considering the computer models over the last days have wanted to develop a west Caribbean tropical cyclone for the latter part of June...it makes sense to be paying strong attention to TD 3-E...tropical wave...and Panama upper anticyclone. TD 3-E seems to have added clarity on how all this will play out...but also has changed things up a bit. Based on the latest discussion and forecasts from the NHC on 3-E...and based on the latest computer model runs...it seems the Panama upper anticyclone is deep-layered enough to steer TD 3-E slowly NW into the S coast of Mexico. I forecast that the highest level of the upper anticyclone will shift west while becoming increasingly associated with strengthening 3-E's latent heat release...and this could be a particularly dangerous situation for the S coast of Mexico if the 200 mb layer of the anticyclone aligns directly over 3-E...which would support healthy upper outflow and rapid strengthening of 3-E. As the upper anticyclone shifts west...this will support unfavorable shearing northwesterlies (and a wake upper trough in the central Caribbean as we are beginning to see)...all of which would prevent tropical cyclone activity in the Caribbean. After 3-E and expansive upper anticyclone make landfall in SE Mexico...there are some model runs suggesting the upper anticyclone would support another tropical cyclone on the Atlantic side of things from June 20 to 23 (starting in the Bay of Campeche tracking across the Gulf of Mexico). Considering typical model performance a week out...taking this scenario superficially at this time...but will definetly be on the lookout as we get closer to June 20.

P11...Upper ridge in E tropical Atlantic has dissipated as the upper-levels of anticyclone in paragraph P5 gains strength from warm air advection ahead of deep-layered 1009 mb cyclone discussed in paragraph P4. As the anticyclone in paragraph P5 continues to gain strength to the north...the E tropical Atlantic is actually reversing into upper vorticity based on latest 200 mb wind barbs in the above atmospheric features chart. Meanwhile...upper ridging has developed to the S of the 1009 mb deep-layered cyclone (where upper-level pressures are relatively higher)...located across the E Caribbean and central tropical Atlantic.

P12...Tropical wave WSW of the Cape Verde Islands 24 hrs ago is approaching the Lesser Antilles tonight...but is under a hostile westerly shear enivronment on the north side of the upper ridge mentioned at the end of paragraph P11 above.

P13...A tropical wave has been added to the NHC TAFB analyses (and likewise toward the lower-right corner above charts) while emerging from western Africa. Since the E tropical Atlnatic is reversing to upper vorticity (as explained in paragraph P11 above)...upper winds will be unfavorable for this tropical wave to develop.

Updated: 5:30 AM GMT on June 14, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #26

By: NCHurricane2009, 2:55 AM GMT on June 13, 2012

...JUNE 12 2012...10:57 PM EDT...
Tonight...watching NW Atlantic for possible subtropical cyclone development. Caribbean Sea activity is increasing. See paragraphs P2 and P6 for further details on these situations.

...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 anlaysis, 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 indicating surface lows, Hs indicating 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...Strong surface frontal cyclone persists over Canada's Hudson Bay...still supported by divergence ahead of vigorous central US upper trough. Convergence behind central US upper trough supports a 1024 mb ridge marked in the above charts. 1017 mb low in W North Carolina has weakend to a SE US pre-frontal surface trough in last 24 hrs. Warm air advection ahead of Hudson Bay frontal cyclone supports east US upper ridge that extends along the Gulf coast. Westerly flow at the base of the central US upper trough diverges with northerly flow across Gulf coast portion of upper ridge...this divergence supporting surface lows of 1014 mb (N Texas) and 1017 mb (LA/MS/AK border)...along the cold front extending far from the Hudson Bay cyclone. The upper ridge's eastern convergence supports surface 1022 mb centers offshore of Atlantic Canada.

P2...Upper vortex in NW Atlantic persists...and remains stacked above 1010 mb frontal low. Accelerational divergence SE of this upper vortex still supports a bare surface front across the central Atlantic...a fragment of which has decayed into a surface trough over the central Bahamas. This surface trough may merge with N end of Caribbean Sea tropical wave (mentioned in paragraph P6 below). The 1010 mb frontal low below the upper vortex has begun firing convective cloudiness...perhaps as the upper vortex is cold enough to de-stabilize the atmosphere despite waters of 23 deg C. Albeit...I would like to see convective cloudiness fire much closer to the center than currently seen to more seriously consider this a candidate for subtropical development. If convective cloudiness does not improve from current structure in the next 24 hours...I will be calling off this area for subtropical development.

P3...Deep-layered anticyclone S of the Azores (with surface center of 1030 mb) has vertically re-coupled.

...TROPICAL BELT DISCUSSION...
P4...In yesterday's discussion (paragraph P1)...upper trough associated with Hudson Bay cyclone was absorbing an old central US upper trough. What has not been absorbed is across the Gulf of Mexico tonight.

P5...East-west upper trough remains across the Caribbean Sea. Upper vorticity midway between the Lesser Antilles and Azores persists. Remainder of the dry air in the tropical belt at this time has collected beneath both these upper features...when looking at tonight's thermodynamic birdseye chart.

P6...Long-lived Caribbean upper ridging persists...currently forked in half by east-west upper trough of paragraph P5. The northern half is an upper anticyclone over Cuba...the southern half is an upper anticyclone near Panama which continues to fire strong t-storms over the surface ITCZ in the area. Tropical wave that was over the Lesser Antilles yesterday (discussion #25 paragraph P9) is zooming west across the Caribbean and may add fuel to the disturbed weather beneath the Panama upper anticyclone. If so...the Panama upper anticyclone would intensify via latent heat release of the t-storm activity...and in turn the upper anticyclone would aid in outflow for surface pressure falls and tropical development. Considering computer models have wanted to flare up the upper anticyclonicity in this region (and develop a tropical cyclone beneath it)...we will be watching this carefully. To be honest...the models have wanted to develop this tropical cyclone activity no sooner than June 18...almost suggesting that tonight's Panama upper anticyclone/surface tropical wave pair is not what the models have been developing. The GFS model solution for future Caribbean tropical activity is complex tonight...suggesting that the upper trough in paragraph P1 and upper vortex in paragraph P3 merge..afterwards the merger leaving behind an upper vortex offshore of SE US that entagles itself with a 1st tropical-to-subtropical cyclone that tracks from the Caribbean to Bahamas (June 18 to 20 timeframe). The GFS then develops a 2nd Caribbean tropical cyclone that tracks into the Bay of Campeche (June 20 to 24 timeframe).

P7...Upper ridge in E tropical Atlantic continues to keep air moist in the area thanks to its upper outflow.

P8...Tropical wave passing S of the Cape Verde Islands 24 hrs ago is WSW of those islands tonight. It has left the favorable upper ridge mentioned in paragraph P7...entering less favorable dry air and westerly vertical shear associated with features in paragraph P5 above.

Updated: 2:57 AM GMT on June 13, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #25

By: NCHurricane2009, 2:48 AM GMT on June 12, 2012

...JUNE 11 2012...10:53 PM EDT...
The following is an update on three prospect areas of tropical development mentioned in previous discussion #24:

The cut-off upper low forecasted by numerical models to occur in the NW Atlantic...by June 13 to 15...is coming to fruition as explained by tonight's paragraph P3. I believe there is a slight chance of a subtropical cyclone in the NW Atlantic during the June 13 to 15 timeframe from this system...see paragraph P3 for further details.

1009 mb Gulf coast low is translating across the SE US as a 1017 mb feature tonight...and headed towards the west Atlantic (see paragraph P1). The only upper atmospheric feature that can help it become a tropical system is upstream upper ridge mentioned towards the end of paragraph P1. The numerical models seem to squeeze out the upper ridge between upper trough in paragraph P1 and upper vortex in paragraph P3...so I don't expect this area to become a W Atlantic tropical cyclone. Instead...I expect it will eventually get absorbed/assimilated into the SW side of weather system in paragraph P3 in the coming days.

Computer models continue flaring Caribbean upper ridging (paragraph P7 below) and suggesting a possible tropical cyclone beneath it for the latter part of June. However...the "tropical cyclone" displayed by the models is a bit scattered about...and I still don't know which current surface feature (if any) will come into play. One could argue that the surface tropical wave in paragraph P9 below maybe what the models are talking about...but I am suspicious because the tropical wave has made a recent NW jog toward the deep-layered cyclonic system of paragraph P3 instead of a direct W jog into the Caribbean.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1921Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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 cyclone from west coast of North America has moved rapidly eastward while intensifying to 989 mb...and reaching Canada's Hudson Bay. Intensification of the surface cyclone is supported by divergence ahead of vigorous west US upper trough. West US upper trough has absorbed central US upper trough mentioned in paragraph P1 of yesterday's discussion. 1009 mb Gulf coast low (paragraph P1 of yesterday's discussion) has moved NE into W North Carolina and is at 1017 mb while guided by southwesterly flow ahead of strong 989 mb frontal cyclone. This has brought the heavy rains along the Gulf coast into interior sections of the SE US. Strong warm air advection ahead of 989 mb cyclone has amplified the east US upper ridge ahead of this system. The upper ridge's eastern convergence supports surface ridge centers of 1024 mb offshore of Carolinas...1026 mb centers over Atlantic Canada...and 1028 mb over S Greenland.

P2...What is left ofupper vortex SE of Greenland is an upper trough exiting the picture while heading toward W Europe. Decaying surface low of 1019 mb SE of Greenland in the above charts...once supported by this upper vortex...will soon dissipate.

P3...Relatively new upper vortex in NW Atlantic continues pushing southward and amplifying while the adjacent upper ridge...mentioned towards the end of paragraph P1...amplifies to its west. This is something numerical models have been predicting to occur. 24 hrs ago...this upper vortex supported a 1011 mb cyclone with divergence at its NE periphery...which is now almost vertically stacked with the upper vortex and is currently at 1010 mb. Also 24 hrs ago...accelerational divergence SE of this upper vortex supported a new 1010 mb frontal low in the central Atlantic...but all that is left now is a bare surface front across the central Atlantic tonight. I beleive there is a slight chance that the 1010 mb surface low near the upper vortex could begin firing t-storms and hence become more subtropical...that is if the upper vortex is cold enough to de-stabilize the atmosphere despite waters in the area in the low 20s of deg C. I will be calling off this area for subtropical development if t-storm clouds do not begin showing near the 1010 mb center by June 13.

P4...Deep-layered anticyclone S of the Azores has begun to vertically de-couple...with surface 1030 mb center remaining S of the Azores while the upper anticyclonic center has been displaced eastward toward the Canary Islands thanks to the vigor of the upper vortex in paragraph P3.

P5...Upper ridge on east coast of Canada has merged with east US upper ridge mentioned towards the end of paragraph P1.

...TROPICAL BELT DISCUSSION...
P6...East-west upper trough straddling the Atlantic tropics has split into a fragment across the Caribbean and upper vortex midway between the Antilles and Azores. Remainder of the dry air in the tropical belt at this time has collected beneath this upper trough when looking at tonight's thermodynamic birdseye chart.

P7...Long-lived Caribbean upper ridging persists...currently forked in half by east-west upper trough of paragraph P6. The northern half is an upper anticyclone near Cuba...the southern half is an upper anticyclone over Panama which has helped to fire strong t-storms over the surface ITCZ in the area.

P8...Upper ridge in E tropical Atlantic continues moistening the air in the area thanks to its upper outflow.

P9...Tropical wave nearing the Lesser Antilles in yesterday's discussion has made it to the northern Antilles while gaining a SW-NE tilt in latest NHC TAFB maps...suggesting it is gravitating NW toward subtropical ridge weakness caused by deep-layered low pressure system in paragraph P3 above. Currently...this tropical wave is inactive while suppressed by dry air of east-west upper trough mentioned in paragraph P6.

P10...Tropical wave that emerged from Africa yesterday is passing S of the Cape Verde Islands tonight. It is travesring favorable moistening air and upper outflow caused by upper ridge in paragraph P8...so there is a chance that it may get increasingly impressive on satellite imagery in the short-term. This tropical wave is doomed for a one-two punch of dry air & westerly vertical shear in the long-term thanks to upper trough mentioned in paragraph P6 above.

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #24

By: NCHurricane2009, 8:36 PM GMT on June 10, 2012

...JUNE 10 2012...4:37 PM EDT...
After the unusual pre-season tropical activity in the Atlantic...prospecting for new activity in the latter part of June.

The unusual pre-season activity appears associated with the equally unusual "loopy" jet stream (with high amplitude upper troughs and ridges) seen this year. Every instance of pre-season activity was associated with cut-off upper vortices left behind by the loopy jet stream. Divergence on the periphery of the cut-off upper vortex triggers a surface cyclone...the shear reducing when the surface cyclone aligns with the upper vortex. Cold temps of the upper vortex de-stabilizes the atmosphere for t-storms and tropical development of the surface cyclone...in some cases above waters less than 26 deg C. For example...see the following statements made earlier on the blog this year concerning how cut-off upper vortices triggered subtropical/tropical development:

Discussion #1...4th and 5th paragraphs of west-to-east discussion...for prelude to Invest 91-L

Discussion #2...4th 5th and 6th paragraphs of west-to-east discussion...for prelude to Invest 91-L

Discussion #4...5th and 6th paragraphs of Open Atlantic Waters Discussion...for prelude to Invest 91-L

Discussion #10...special feature section...for Invest 92-L

Discussion #12...1st special feature section...for prelude to Tropical Storm Alberto

Discussion #17...Special feature section....for Tropical Storm Beryl

Looking ahead...here are some prospects for Atlantic tropical activity in the latter part of June. None of these propsects appear imminent at this time.

Concerning the mid-latitudes...numerical models (like GFS) had been developing an impressive cut-off upper low for June 13 to 15 during discussion #22..then backed of developing a cut-off upper low during discussion #23. The cut-off upper low was slated to develop from the weather system mentioned in paragraph P2 of today's discussion. Numerical models have now re-instated the development of this cut-off upper low...which is a merger of the SW-NE upper trough axis in paragraph P2 and upper vortex in paragraph P3. I believe there is a slight chance of a NW Atlantic subtropical cyclone from the forecasted cut-off upper low beginning June 13...see last sentences of paragraph P3 for further details.

From forecast surface maps generated by numerical models...it seems the 1009 mb Gulf coast low (paragraphs P1 and P2) will translate across the SE US and into the west Atlantic by June 15 and onwards. This system may merge with cold front of frontal cyclone currently moving in from west coast of North America (paragraph P1). Or alternatively...I believe there is a slight chance it could thrive under the upstream upper ridge (mentioned at end of paragraph P1) and become a W Atlantic tropical cyclone.

Concerning the tropical belt...computer models began flaring Caribbean upper ridging (paragraph P6 below) and developing a tropical cyclone beneath it (days after June 15)....for example see intro section of previous discussion #23. The GFS model is not displaying this solution as aggressively today...but we will be on the lookout as we get closer to this timeframe.

...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 anlaysis, 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 indicating surface lows, Hs indicating 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 cyclone in SW Canada (in previous discussion #23) has been absorbed by a second cyclone moving into the west coast of North America. This second cyclone's center is not yet in the scope of the above charts...but its associated upper trough is now in the western US. Remnant upper trough once associated with the absorbed cyclone is now over the central US while absorbing a south Texas cut-off upper low (origins of cut-off upper low mentioned in previous discussion #23). Divergence E of this central US upper trough has been supporting heavy weather over the stalled SE US front mentioned in paragraph P2 below. This persistent heavy weather has caused flooding along parts of the US Gulf coast. Stalled SE US front has transitioned to a 1009 mb coastal Louisiana low supported by the central US upper trough...which unfortunately means heavy weather will persist along parts of the US Gulf coast. Finally...the upper ridge associated with warm air advection ahead of this complex weather system is now over the eastern US...and the upper ridge's eastern convergence supports surface ridge centers of 1020 mb in West Virginia...1021 mb near Bermuda...1020 mb over the NE US...and 1023 mb over SE Canada.

P2...Longwave upper trough in the western Atlantic consisted of an SW-NE-tilted axis and upper vortex over Atlantic Canada in previous discussion #23. Its SW-NE axis has now merged with a relatively-new frontal system covered in paragraph P3...and the upper vortex is now just SE of Greenland. The upper vortex featured a mature 996 mb surface cyclone in discussion #23...which has now weakened to 1011 mb in the above charts (while suffering from a lack of divergence beneath the upper vortex). At the surface...this system consisted of a long stalled front reaching into the SE US. This long stalled front no longer belongs with this system. One fragment is now a 1009 mb Gulf coast low mentioned in paragraph P1 above. Another fragment belongs to a new 1010 mb low mentioned in paragraph P3 below.

P3...Although not mentioned in previous discussions...a new frontal system has been emerging over Canada's Hudson Bay over the last days. Frontal system at the surface now consists of a 1011 mb cyclone & cold front pushing into the NW Atlantic...supported by divergence at the NE periphery of an upper vortex. Accelerational divergence SE of this upper vortex also supports a new 1010 mb frontal low in the central Atlantic. This new upper vortex has been spinning up in relatively low pressures between the upper ridge mentioned in paragraph P1 above and upper ridge in paragraph P5 below. This new upper vortex has also absorbed the SW-NE titled upper trough axis mentioned in paragraph P2 above. Upper vortex is expected to push SE across the NW Atlantic (above 23 to 24 deg C water) and amplify while the adjacent upper ridge in paragraph P1 amplifies to its west. I believe there is a slight chance that this upper vortex may be cold enough for subtropical cyclone development at the surface despite water temps below 26 deg C...during the June 13 to 15 timeframe later this week.

P4...Longwave upper trough regime across the entire high seas of the Atlantic is replaced by relatively-new upper anticyclone in the above birdseye charts...located S of the Azores...and caused by warm air advection ahead of system in paragraph P2. Surface 1025 mb Atlantic ridge in this area is now 1030 mb and vertically stacked with this upper anticyclone...creating a deep-layered anticyclone. In previous discussion #23 paragraph P3...what was left of the old upper trough regime was a cut-off upper trough in the central Caribbean...cut-off upper low midway between Lesser Antilles and Azores...and cut-off upper trough over over the Cape Verde Islands. All of these cut-off features are now a single east-west upper trough from the Caribbean Sea to Cape Verde Islands. This east-west upper trough will be moved to the tropical belt section of future discussions.

P5...Full-fledged and anomalous upper anticyclone over the east coast of Canada (paragraph P4 of previous discussion #23) has weakened to an upper ridge. Its eastern convergence supports a 1027 mb ridge S of Greenland.

...TROPICAL BELT DISCUSSION...
P6...Long-lived Caribbean upper ridging persists...currently forked in half by east-west upper trough mentioned towards the end of paragraph P4 above. The northern half is an upper anticyclone over Cuba...the southern half is an upper anticyclone N of Panama.

P7...Upper ridge in E tropical Atlantic has been pushed SE by east-west upper trough mentioned towards the end of paragraph P4. We had been talking about how the south side of this upper ridge...in conjunction with the south side of deep-layered anticyclone in paragraph P4...was wafting in dry air from Africa's desert. The more SE position of the E tropical Atlantic upper ridge has increased outflow over the area such that rising motion below this outflow has re-moistened the air. What's left of that dry air is in the east half of the Caribbean and central tropical Atlantic (using today's thermodynamics birdseye chart).

P8...Tropical wave WSW of Cape Verde Islands in discussion #23 has been moving west and is nearing the Lesser Antilles this afternoon. Currently...this tropical wave is inactive while suppressed by dry air (mentioned in last sentence of paragraph P7 above) and westerly vertical shear south of the east-west upper trough (mentioned towards the end of paragraph P4 above).

P9...Tropical wave has been added to NHC TAFB analyses (and likewise added into lower-right corner of the above charts) while emerging from west Africa. While it is entering the moistening air beneath the ridge of paragraph P7...it is experiencing unfavorable westerly vertical shear on the NE side of that same upper ridge.

Updated: 9:07 PM GMT on June 10, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #23

By: NCHurricane2009, 4:19 AM GMT on June 08, 2012

...JUNE 7 2012...11:59 PM EDT...
After the unusual pre-season tropical activity in the Atlantic...no signs of new tropical activity as the Atlantic Hurricane Season officially starts.

The unusual pre-season activity appears associated with the equally unusual "loopy" jet stream (with high amplitude upper troughs and ridges) seen this year. Every instance of pre-season activity was associated with cut-off upper vortices left behind by the loopy jet stream. Divergence on the periphery of the cut-off upper vortex triggers a surface cyclone...the shear reducing when the surface cyclone aligns with the upper vortex. Cold temps of the upper vortex de-stabilizes the atmosphere for t-storms and tropical development of the surface cyclone...in some cases above waters less than 26 deg C. For example...see the following statements made earlier on the blog this year concerning how cut-off upper vortices triggered subtropical/tropical development:

Discussion #1...4th and 5th paragraphs of west-to-east discussion...for prelude to Invest 91-L

Discussion #2...4th 5th and 6th paragraphs of west-to-east discussion...for prelude to Invest 91-L

Discussion #4...5th and 6th paragraphs of Open Atlantic Waters Discussion...for prelude to Invest 91-L

Discussion #10...special feature section...for Invest 92-L

Discussion #12...1st special feature section...for prelude to Tropical Storm Alberto

Discussion #17...Special feature section....for Tropical Storm Beryl

As the jet stream lifts northward during the peak summer months...we are seeing fewer cut-off upper vortices capable of tropical development...and so the source of development is now transitioning mainly to tropical waves of African origin. As tonight's birdseye charts show...conditions are unfavorable for a tropical wave to develop. The eastern tropical Atlantic is covered by dry air (paragraph P6). The Gulf of Mexico and eastern Caribbean are seeing unfavorable vertical shear. The western Caribbean is seeing upper ridging (paragraph P5)...but the upper ridge is oscillating in and out of the western Caribbean. When it oscillates away into the eastern Pacific (like it is tonight)...it provides unfavorable westerly and northerly vertical shear. When it oscillates back into the western Caribbean...it reduces the shear and enhances outflow favorable for tropical development.

Concenring the tropical belt...the GFS model thru June 23 shows the aforementioned unfavorable patterns continuing...so the only possibility of tropical development during this window is if a tropical wave can sneak under the west Caribbean upper ridging on an oscillation back into the area. In fact...the GFS model today flares up the west Caribbean upper ridge and develops a tropical cyclone beneath it towards June 23.

Concerning the mid-latitudes...the GFS model has backed off developing a cut-off upper low in the open central Atlantic (June 13 to 15). Yesterday...the GFS model had developed this cut-off upper low from the weather system currently mentioned in paragraph P2.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1950Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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...West US upper trough supports a surface frontal cyclone in SW Canada. This cyclone in the last 24 hrs has actually tracked NW toward another moving into the west coast of North America. Warm air advection ahead of this cyclone still supports an upper ridge from Texas to Manitoba...and another upper ridge axis over New Mexico. An upper trough over S Texas formed between these two upper ridge axes yesterday...perhaps where warm air advection has not been as strong. This S Texas upper trough has amplified into an upper low.

P2...Longwave upper trough over eastern US is moving into the western Atlantic. It still consists of a SW-NE-tilted axis and upper vortex over Atlantic Canada (cut-off to the SW of paragraph P4 upper anticyclone). Divergence ahead of the SW-NE upper trough supports a stalled front over the SE US that extends to a 996 mb cyclone that has made landfall over SE Newfoundland. This surface cyclone has moved underneath the upper vortex...resulting in a deep-layered low altogether where the surface cyclone will now begin weakening benath the less divergent upper vortex. Convergence behind the SW-NE upper trough (with respect to paragraph P4 upper anticyclone) supports a 1021 mb central US ridge...1013 mb ridge over NE Canada...and 1020 mb ridge over S Greenland.

P3...Longwave upper trough regime across the entire high seas of the Atlantic continues breaking up...becoming replaced by a new upper anticyclone in the above birdseye charts...located S of the Azores...and caused by warm air advection ahead of the 996 mb cyclone in paragraph P2. Remnant upper trough and associated surface cyclone approaching western Europe have made landfall. Remnant cut-off upper trough in eastern Caribbean is moving W into the central Caribbean while steered by Caribbean upper ridging in paragraph P5. Remnant cut-off upper low (midway between Lesser Antilles and Azores) is being pushed south by new upper anticyclone mentioned earlier in this paragraph. Remnant upper trough over the Canary Islands is now cut-off over the Cape Verde Islands...to the SE of new upper anticyclone mentioned earlier in this paragraph. Surface 1027 mb open Atlantic ridge in this area has weakened to 1025 mb in the last 24 hrs.

P4...Full-fledged and anomalous upper anticyclone over the east coast of Canada persists.

...TROPICAL BELT DISCUSSION...
P5...Long-lived Caribbean upper ridging persists. Accelerationally-divergent upper westerly jet across the Gulf of Mexico persists due to the pressure gradient between this upper ridge...upper trough in paragraph P2...and S Texas cut-off upper low in paragraph P1. Disturbed weather and surface troughs produced by the upper jet's divergence is becoming assimilated into SE US stalled front mentioned in paragraph P2.

P6...Upper ridge in E tropical Atlantic is losing definition against new upper anticyclone mentioned in paragraph P3. Thermodynamics birdseye charts (such as the above) continue suggesting a westward expansion of dry air from Africa's desert...supported by deep-layered easterly flow south of the 1025 mb ridge (paragraph P3)...south of the E Atlantic upper ridge (mentioned in this paragraph)...and south of new upper anticyclone (paragraph P3).

P7...Tropical wave in the eastern Caribbean has been removed from TAFB analyses today as of 1200Z...and likewise has been removed from the above birdseye charts.

P8...Tropical wave that was S of the Cape Verde Islands 24 hrs ago has moved westward...and is now WSW of those islands. Its still suppressed by dry air mentioned in paragraph P6.

Updated: 4:40 AM GMT on June 08, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #22

By: NCHurricane2009, 4:03 AM GMT on June 07, 2012

...JUNE 6 2012...11:59 PM EDT...
After the unusual pre-season tropical activity in the Atlantic...no signs of new tropical activity as the Atlantic Hurricane Season officially starts.

The unusual pre-season activity appears associated with the equally unusual "loopy" jet stream (with high amplitude upper troughs and ridges) seen this year. Every instance of pre-season activity was associated with cut-off upper vortices left behind by the loopy jet stream. Divergence on the periphery of the cut-off upper vortex triggers a surface cyclone...the shear reducing when the surface cyclone aligns with the upper vortex. Cold temps of the upper vortex de-stabilizes the atmosphere for t-storms and tropical development of the surface cyclone...in some cases above waters less than 26 deg C. For example...see the following statements made earlier on the blog this year concerning how cut-off upper vortices triggered subtropical/tropical development:

Discussion #1...4th and 5th paragraphs of west-to-east discussion...for prelude to Invest 91-L

Discussion #2...4th 5th and 6th paragraphs of west-to-east discussion...for prelude to Invest 91-L

Discussion #4...5th and 6th paragraphs of Open Atlantic Waters Discussion...for prelude to Invest 91-L

Discussion #10...special feature section...for Invest 92-L

Discussion #12...1st special feature section...for prelude to Tropical Storm Alberto

Discussion #17...Special feature section....for Tropical Storm Beryl

As the jet stream lifts northward during the peak summer months...we are seeing fewer cut-off upper vortices capable of tropical development...and so the source of development is now transitioning mainly to tropical waves of African origin. As tonight's tropical belt discussion shows...conditions are unfavorable for a tropical wave to develop. The eastern tropical Atlantic is covered by dry air (paragraph P6). The Gulf of Mexico and eastern Caribbean are seeing unfavorable vertical shear (see paragraphs P5 and P7). The western Caribbean is seeing upper ridging (paragraph P5)...but the upper ridge is oscillating in and out of the western Caribbean. When it oscillates away into the eastern Pacific (like it is tonight)...it provides unfavorable westerly and northerly vertical shear. When it oscillates back into the western Caribbean...it reduces the shear and enhances outflow favorable for tropical development.

Concenring the tropical belt...the GFS model thru June 22 shows the aforementioned unfavorable patterns continuing...so the only possibility of tropical development during this window is if a tropical wave can sneak under the west Caribbean upper ridging on an oscillation back into the area.

Concerning the mid-latitudes...the GFS model shows a decent cut-off upper low in the open central Atlantic (June 13 to 15) originating from the weather system currently mentioned in paragraph P2. Could this cut-off upper low trigger tropical development like we have been seeing in the pre-season? So far...GFS does not show anything very impressive at the surface in association with the forecasted cut-off upper low.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1324Z-released HPC analysis.

In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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...Divergence east of a west US upper trough supports a surface frontal cyclone that has moved from Montana into SW Canada. Warm air advection ahead of this cyclone supports an upper ridge from Texas to Manitoba...and another upper ridge axis over New Mexico. An upper trough over S Texas has formed between these two upper ridge axes...perhaps where warm air advection has not been as strong.

P2...Longwave upper trough regime over eastern US continues. It still consists of a SW-NE-tilted upper trough and upper vortex near Atlantic Canada (cut-off to the SW of paragraph P4 upper anticyclone). Divergence ahead of the SW-NE upper trough supports a stalled front over the SE US that extends to a 997 mb cyclone offshore of Atlantic Canada. Convergence behind the SW-NE upper trough (with respect to paragraph P4 upper anticyclone) supports a 1022 mb Michigan ridge and 1026 mb ridge over the east coast of Canada.

P3...Longwave upper trough regime across the entire high seas of the Atlantic is breaking up today. Its upper vortex is no longer cut-off...and is now accelerating as an upper trough toward western Europe. Decaying surface cyclone and its cold front is also heading toward western Europe. Other features of this regime include an upper trough that is becoming cut-off into the eastern Caribbean...another upper trough midway between the Antilles and Azores that has become a cut-off upper low...and a third upper trough over the Canary Islands. Surface 1027 mb open Atlantic ridge was supported by convergence W of the Canary Islands upper trough 24 hrs ago...but is now being supported by convergence on the NW side of the cut-off upper low midway between the Antilles and Azores.

P4...Full-fledged and anomalous upper anticyclone over S Greenland 24 hrs ago is now over the east coast of Canada tonight.

...TROPICAL BELT DISCUSSION...
P5...Long-lived Caribbean upper ridging persists. Accelerationally-divergent upper westerly jet across the Gulf of Mexico persists due to the pressure gradient between this upper ridge and upper trough regime in paragraph P2. The divergent aspect of the upper jet supports continued t-storms across the Gulf of Mexico...and a new surface trough in the W Gulf of Mexico. Westerly aspect of the upper jet continues to shear these t-storms and prevent tropical development.

P6...Upper ridge in E tropical Atlantic has expanded westward toward the Lesser Antilles...the expansion caused by the weakening of adjacent upper trough regime in paragraph P3. Animation of thermodynamics birdseye charts (such as the above) since June 1 suggests a westward expansion of dry air from Africa's desert...supported by deep-layered easterly flow south of the 1027 mb ridge (paragraph P3)...and south of the E Atlantic upper ridge (mentioned in this paragraph).

P7...A tropical wave has crossed the Lesser Antilles (into the eastern Caribbean) and remains at the west end of paragraph P6 upper ridge...where it has found enhanced poleward outflow and hence why it has persistent t-storms. However...this tropical wave is battling southerly vertical shear from the east Caribbean cut-off upper trough (mentioned in paragraph P3).

P8...A tropical wave is S of the Cape Verde Islands and towards the east end of paragraph P6 upper ridge. This tropical wave is suppressed by dry air mentioned in paragraph P6.

Updated: 4:45 AM GMT on June 08, 2012

Permalink

2012 Atlantic Hurricane Season Birdseye Discussion #21

By: NCHurricane2009, 3:50 AM GMT on June 06, 2012

...JUNE 5 2012...11:55 PM EDT...
After the unusual pre-season tropical activity in the Atlantic...no signs of new tropical activity as the Atlantic Hurricane Season officially starts. What caused the early activity...followed by an outlook of potential activity in the next several days...will be discussed here in the next day or two.

...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 anlaysis, 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 indicating surface lows, Hs indicating 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 upper trough in mid-latitudes is entering the picture from the upper-left of the above birdseye charts...over the western US. Divergence east of this upper trough supports a surface frontal cyclone over Montana. Warm air advection ahead of this Montana cyclone supports an upper ridge from western Texas to the Manitoba province of Canada. Upper westerlies across the upper ridge axis...coupled with low-level southerlies ahead of the Montana cyclone..is allowing for directional wind shear favoring severe T-storms and tornadoes in Montana tonight.

P2...Over the eastern US...there has been a longwave upper trough regime with embedded shortwaves swinging through. This longwave upper trough regime contains the remnants of the frontal system in paragraph P1 of discussion #20. Tonight...the longwave upper trough regime consists of a SW-NE-tilted upper trough and upper vortex near Atlantic Canada (cut-off to the SW of paragraph P4 upper anticyclone). Divergence ahead of the SW-NE upper trough supports a stalled front over the southern tier of the US that extends to a 998 mb cyclone offshore of Atlantic Canada. Convergence behind the SW-NE upper trough (with respect to paragraph P4 upper anticyclone) supports a 1021 mb Michigan ridge and 1030 mb ridge near the east coast of Canada.

P3...See paragraph P3 of previous discussion #20 for longwave upper trough regime across the entire high seas of the Atlantic. This longwave upper trough still has an upper low vortex at its north end while cut-off to the south of the upper anticyclone in paragraph P4. At the surface...dominant feature is decaying cyclone south of Greenland currently at 1001 mb (1330Z HPC) that once was 988 mb in discussion #20. Other features of this regime include an upper trough across the Lesser Antilles...another upper trough midway between the Antilles and Azores...and a third upper trough over the Canary Islands. Subtropical surface ridging several days ago was supported by upper anticyclone in paragraph P4. This surface ridging is regaining intensity tonight...as a 1027 mb center supported by convergence W of the Canary Islands upper trough.

P4...Full-fledged and anomalous upper anticyclone west of the British Isles is centered over S Greenland tonight.

...TROPICAL BELT DISCUSSION...
P5...Long-lived Caribbean upper ridging persists. There is an accelerationally-divergent upper westerly jet north of this ridge and south of the regime in paragraph P2...the divergent aspect allowing for t-storms across the Gulf of Mexico. The strong westerly aspect is also causing very high vertical shear unsuited for tropical development with these t-storms.

P6...Tropical wave in paragraph P7 of discussion #20...which was nearing the Lesser Antilles...has dissipated and has been removed from the NHC TAFB analyses days ago.

P7...Upper ridge in E tropical Atlantic has expanded westward toward the Lesser Antilles...the expansion caused by the weakening of adjacent upper trough regime in paragraph P3. Animation of thermodynamics birdseye charts (such as the above) since June 1 suggests a westward expansion of dry air from western Africa...supported by deep-layered easterly flow south of the 1027 mb ridge (paragraph P3)...and south of the E Atlantic upper ridge (mentioned in this paragraph).

P8...A tropical wave approaching the Lesser Antilles is at the west end of paragraph P7 upper ridge...where it has found enhanced poleward outflow and hence why it has seen an increase in t-storms. However...this tropical wave will soon encounter hostile southerly vertical shear from the Lesser Antilles upper trough (mentioned in paragraph P3).

P9...A tropical wave is S of the Cape Verde Islands and towards the east end of paragraph P7 upper ridge. This tropical wave is suppressed by dry air mentioned in paragraph P7.

Updated: 1:36 AM GMT on June 07, 2012

Permalink

About NCHurricane2009

NCHurricane2009 doesn't have a bio yet.

NCHurricane2009's Recent Photos