2012 Atlantic Hurricane Season Birdseye Discussion #3

By: NCHurricane2009 , 12:02 AM GMT on April 15, 2012

...APRIL 14 2012...
This is the third "birdseye" discussion of the 2012 Atlantic Hurricane Season. I conceived the idea of analyzing the entire Atlantic basin from two maps that provide a "birdseye" view of the region. I found this method useful for understanding the day-to-day evolution of the Atlantic basin throughout Hurricane Season 2011.

Atlantic Hurricane Season does not start until June 1. However, this discussion is issued due to persistent computer model support for subtropical cyclone formation in the central Atlantic during the next days.


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.


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).

System over the western United States continues to become more complex in last 48 hours. Aloft, the system is anchored by west US upper trough still stationary over the eastern borders of California and Nevada. The vigorous surface cyclone (with multiple pressure centers below 1000 mb) that the west US upper trough supported has ejected northward into SW Ontario and weakened to 1001 mb. As it ejected, local cool air advection on its west side has supported the formation of small upper low vortex over SE Manitoba. The central US upper ridge supported by warm air advection east of the 1001 mb cyclone has shifted into the eastern US overnight. This 1001 mb cyclone produced a severe weather convective mass over Oklahoma last evening that has since moved ENE into Missouri and Ohio valley, a position beneath the east US upper ridge. This convective mass is now embedded in a lower shear environment among deep-layered westerlies in the east US upper ridge and SE of the 1001 mb cyclone. The reduction in shear across the convective mass means that is a lower risk of severe weather, but still has embedded thunderstorms.

The west US upper trough no longer supports the SW Ontario 1001 mb cyclone. The 1001 mb cyclone is now being supported by divergence between the SE Manitoba upper low and east US upper ridge. The west US upper trough instead supports another vigorous surface cyclone with multiple pressure centers below 1000 mb that has rolled in from California overnight. This SW US surface cyclone, new to this discussion, has a 990 mb center over Colorado and 995 mb center over SW Utah in the above charts. This SW US surface cyclone is extremely dangerous today as it produces southerly flow pushing in low-level warmth/moisture, which collides with cooler upper westerly flow en route to the east US upper ridge, favoring directional wind shear and instability for an extreme severe weather event across Oklahoma, Kansas, Nebraska, parts of Iowa, and parts of Missouri. Convective cloud tops on satellite and supercell T-storm signatures on radar are rapidly flourishing throughout the day, and residents in this area are urged to listen to local media for this dangerous severe weather event.

As discussed above, central US upper ridge has been pushed into east US by the 1001 mb surface cyclone in SW Ontario. As a result, the surface ridge supported by the convergent east side of the upper ridge has also shifted east. This surface ridge now has a single 1029 mb center just offshore of Cape Lookout, North Carolina.

Mentioned briefly in yesterday's discussion was a N Quebec 1008 mb cyclone that has marched across Hudson Bay. Since then, the cyclone has continued an ESE march and depeened to 1005 mb just NW of Newfoundland. Its associated shortwave upper trough has merged with prominent upper trough offshore of east US, and its western convergent side is supporting a 1019 mb surface ridge currently over the southern Hudson Bay.

High seas south of Greenland dominated by rapidly intensifying surface cyclone moving quickly NNE from Newfoundland. Yesterday's discussion mentioned this cyclone at 1003 mb and that it had stopped intensifying as it moved beneath a non-divergent upper low along the upper trough offshore of east US. Since then, the upper low has been absorbed by shortwave upper trough associated with above-discussed 1005 mb cyclone from N Quebec. Moreover, this shortwave upper trough has merged with the large upper trough offshore of east US, and in turn mass divergence east of the large upper trough has caused explosive intensification of yesterday's 1003 mb cyclone which has now rapdily deepeend to 985 mb as of the 1330Z HPC analysis. Expect the neighboring 1005 mb cyclone from N Quebec to become absorbed by the rapidly deepening 985 mb cyclone. This rapidly deepening cyclone will cause rough weather in the high seas south of Greenland as well as land areas of south Greenland.

Extending south of rapidly intensifying cyclone S of Greenland is a long cold front that has been attached to the cyclone, and also has been an area of interest for future subtropical cyclone formation. Yesterday's discussion of the cold front mentioned a 1008 mb low that formed east of Bermuda, but since then the 1008 mb low has been assimilated into the growing low pressure field of rapidly deepening cyclone S of Greenland. Further south, the cold front has pushed into the Dominican Republic and Puerto Rico and absorbed the non-frontal surface trough that was located north of Puerto Rico 24 hours ago.

Central Atlantic deep-layered ridging has been pushed toward east Atlantic ahead of rapidly deepneing cyclone S of Greenland and its very long oceanic cold front. The southern portion of the upper ridge has stopped amplifying, but the northern portion of the upper ridge is about to amplify further into an upper high located over the Azores due to the intense warm air advection ahead of deepning cyclone S of Greenland. Northerly convergent flow east of the amplifying upper ridge continues to support the strong surface ridge near the Azores which today is at 1031 mb. Expect the developing upper high and 1031 mb surface center to become aligned, which will result in an impressive blocking deep-layered high pressure centered over the Azores.

Computer model runs continue to support subtropical cyclone formation along the oceanic cold front extending from the deepening cyclone S of Greenland. The associated upper trough has been offshore of east US. This morning's GFS model run shows the southern portion of the upper trough becoming cut-off to E of Bermuda tomorow while the northern portion splits away to the NE while "running away" with the deepening cyclone S of Greenland. The cut-off upper trough E of Bermuda gets trapped between the above-discussed blocking Azores ridge and upper ridge over the eastern US mentioned in today's North American discussion. Warm air advection ahead of SW US surface cyclone (producing today's central US severe weather) will amplify the eastern US upper ridge such that the cut-off upper trough E of Bermuda also amplifies into a rather impressive cut-off upper low vortex E of Bermuda by April 17. Whatever is left of the oceanic cold front beneath the east side of the upper low vortex is progged by the models to spin up into a non-frontal subtropical cyclone supported by divergence from the cut-off upper low vortex, the process beginning on April 17.

The models show the subtropical cyclone making a clockwise loop E of Bermuda while steered by the cut-off upper low vortex from the 17th to 19th. Using today's thermodynamics chart, this keeps the forecasted subtropical cyclone well north of the 26 deg C isotherm, over waters between 20 to 22 deg C. It is going to take a very cold-temperature upper low to produce instability and convection with surface water/air temps that mild. The cut-off upper low vortex E of Bermuda developed by the models seems impressive enough to be up to the challenge, so subtropial cyclone formation is still possible...stay tuned!

As forecated in yesterday's discussion, the upper trough in the far east Atlantic has amplified into a cut-off upper low midway between the Cape Verdes and and Azores. The remainder of the upper trough has split off and is pushing toward western Europe, and its eastern divergent has begun to support the weak NE Atlantic extratropical surface low seen in visible satellite yesterday (and also briefly mentioned yesterday). This weak NE Atlantic low had made landfall in west Europe, its tail end showing as a surface trough in today's 1200Z analysis from TAFB. Meanwhile, the divergent east side of the new cut-off upper low (between the Cape Verdes and Azores) has been fighting dry/sinking air that was earlier induced by the deep-layered ridge now developing over the Azores. Water vapor satellite imagery shows the air has moistened over the Cape Verdes, and so the divergent east side of the cut-off upper low may begin to produce some light weather.

Although present, a shortwave upper trough that formed over the SE US (Virginia, Carolinas, and Georgia) was not mentioned yesterday. This shortwave formed yesterday on the west flank of the larger upper trough off of the east US, and was carved out by the amplifying central US upper ridge which has since moved into the eastern US.

As the eastern US upper ridge has moved in, the SE US shortwave upper trough has been pushed southward into the Gulf of Mexico and Florida. Convergence south of the east US upper ridge and north of the Gulf shortwave upper trough is leading to sinking, dry air across the northern Gulf seen in today's thermodynamics chart. Divergence south of the Gulf shortwave upper trough is leading to a batch of moistening air seen over the Yucatan and western Caribbean Sea, but there is not much active weather with this moistening air.

It appears Northern South Amercian monsoon upper ridge continues to be a bit choked by the amplified upper trough near the east US (located due north). Although there is some storm activity remaining with the monsoon, it is not as impressive as it was 48 hours ago.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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