2012 Atlantic Hurricane Season Birdseye Discussion #8

By: NCHurricane2009 , 3:41 AM GMT on April 28, 2012

...APRIL 27 2012...
Central Caribbean Sea tropical disuturbance mentioned in special discusison #7B not expected to develop into a tropical cyclone. However I am resuming full birsdeye discussions in case this changes.

This is the eighth birdseye discussion of the 2012 Atlantic Hurricane Season. See previous discussion #3 concerning the idea behind this new type of discussion forum.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1925Z-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).

In previous full discussion #7...specifically the North America discussion...there was mention of a NW US frontal system with a 1003 mb cyclone over the W Great Lakes that had merged with a central US upper trough. This system eventually moved into the eastern US and triggered an unusually late winter storm (extratropical cyclone) that dumped heavy snow in western New York State and Pennsylvania.

Since then, the associated large upper trough and surface cold front of this winter storm emerged into the western Atlantic. Showers and thunderstorms have greatly increasing across the central Caribbean Sea over the last days as the upper trough/surface cold front interacted with the surface South American monsoon/ITCZ.

Latent heat release continues with these thunderstorms...and the upper flow has responded with warm core upper ridging developing overhead. However...the former winter storm upper trough left a fracture behind in the eastern Gulf of Mexico/Yucatan (marked in above charts)...and this upper trough fracture has maintained strong southerly shear across the disturbance and kept the warm core upper ridge displaced to the east. I do not ever expect tropical cyclone formation with too much vertical shear in the region.

Regardless of tropical cyclone development or not...impacts have been persistent...with the upper southerly flow transporting moisture from this disturbance northward...bringing prolonged rains/flooding potential to Jamaica...Cuba...Haiti...the Dominican Republic...the Cayman Islands...and the Bahamas.

The above special feature discussion mentioned a strong winter storm (extratropical cyclone) that dumped snow earlier in the week in western New York and Pennsylvania. Even today...remnant features of this winter storm remain well-within the above charts. The winter storm barreled northward into Hudson Bay...made a cyclonic loop beneath its parent upper trough...and now has shifted eastward and is a shadow of its former self as a 1003 mb low in north-central Ontario in the above charts. The parent upper trough that once supported it has shifted east into the north-central Atlantic to the south of Greenland and now supports the ex-winter storm's original cold front. This original cold front extends far south into the Atlantic waters east of Bermuda and N of Puerto Rico. Finally...the ex-winter storm left behind an upper trough fracture in the east Gulf of Mexico/Yucatan as mentioned in the above Special Feature discussion.

While the winter storm was making its cyclonic loop over Hudson Bay...an upstream mid-latitude extratropical cyclone and its upper trough snuck in to its south. This extratropical cyclone is now 997 mb over E Maine and this upper trough is over Hudson Bay-to-Massachusetts. Divergence east of this upper trough now supports thie 997 mb cyclone and also the above mentioned ex-winter storm 1003 mb cyclone over north-central Ontario.

A feature that is entering the scope of the above charts is a western US sharp upper trough and equally vigorous surface cyclone. The surface cyclone has a 996 mb center over western Kansas...999 mb center over Colorado...and finally a 997 mb center over NE Wyoming as of 1925Z-released HPC analysis.

Ahead of the NE US winter storm over the past week was immense warm air advection that has developed an upper ridge axis presently stretching from Newfoundland all the way south to the Lesser Antilles.

As this upper ridge amplified...so did a downstream upper trough in the E Atlantic which is still very well-defined in the above charts. This E Atlantic upper trough contains some of the remnant vorticity of last week's Invest 91-L parent upper low. This upper trough's eastern divergence supports a cold front that has pushed southward from W Europe into NW Africa. A well-organized comma-shaped cloud mass SW of the Canary Islands is associated with an upper low vortex that has spun up along the upper trough in the last 24 hours. This upper trough's eastern divergence also generated a new surface trough in this vicinity also 24 hours ago that has since migrated west under the steering of a greater-than-1028 mb ridge NW of the Azores. This surface trough is now midway between the Cape Verde Islands and Lesser Antilles and inactive while now beneath upper-level NW flow convergence west of the upper trough.

The aforementioned greater-than-1028 mb surface ridge NW of the Azores is supported by upper-level NW flow convergence west of the E Atlantic upper trough.

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3. NCHurricane2009
4:15 AM GMT on April 28, 2012
Quoting KoritheMan:
This is so much easier to read now with the advent of a "special features" section highlighting tropical areas of interest.

Much appreciated!

I actually gave you credit in an earlier discussion for this idea. It was an easy add-in.

I am serious about making these better/tailored to what you guys think. I hope to enhance knowledge of what goes on basin-wide each day and help bloggers/lurkers figure out what's going on and learn new things hopefully.
Member Since: September 15, 2009 Posts: 896 Comments: 3957
2. nigel20
4:03 AM GMT on April 28, 2012
Keep up the good work NCH2009 and i'll look forward to your future posts
Member Since: November 6, 2010 Posts: 14 Comments: 9427
1. KoritheMan
4:03 AM GMT on April 28, 2012
This is so much easier to read now with the advent of a "special features" section highlighting tropical areas of interest.

Much appreciated!
Member Since: March 7, 2007 Posts: 644 Comments: 23119

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