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By: NCHurricane2009 , 1:23 AM GMT on April 13, 2012
...APRIL 12 2012...
This is the first "birdseye" discussion of the 2012 Atlantic Hurricane Season, and also my first ever. 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.
...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).
Today's discussion will propagate from the west to east while referring to the above two birdseye charts.
Over the western United States is an upper trough axis currently positioned along the eastern borders of California and Nevada based on the lastest 200 mb wind barbs. Mass divergence east of the upper trough supports a surface non-tropical system, anchored by a 993 mb low at the Montana/Wyoming border and 1006 mb low in south-central New Mexico. Expect the 993 mb low to continue east and be the dominant feature of this non-tropical system, and maintain strength as it is currently well-within the eastern divergence of the west US upper trough. Of note, low-level southerly flow east of the 993 mb low and west of a 1028 mb Kentucky surface ridge is driving warmth and moisture from the south, which collides with cooler westerly flow aloft favoring instability and directional wind shear for severe weather across portions of the central US.
Continuing east, next major weather feature in the birdseye charts is a central US upper ridge. This upper ridge is supported by building warm air from the south courtesy of the flow ahead of the aforementioned 993 mb non-trpoical cyclone. Convergence east of the upper ridge axis supports a surface ridge axis that contains a 1028 mb center over Kentucky, 1027 mb center over NE Ontario, and 1026 mb center over NE Quebec.
Just off the eastern US is a major upper trough supporting an 1004 mb non-tropical cyclone that has just become occluded offshore of Nova Scotia. A brand new upper low has formed on the upper trough axis (east of Massachusetts) due to locally intense cool air advection behind the 1004 mb cyclone. Further amplification of the upper trough/low near the eastern US could be supported by amplification of upstream central US ridge (driven by warm air advection ahead of 993 mb cyclone), and by amplification of upstream west Quebec upper shortwave ridge (driven by warm air advection ahead of cyclone moving across Hudson bay). As this upper trough/low near the east US continues eastward and amplifies, it could support subtropical cyclone formation along the cold front extending from the 1004 mb cyclone...stay tuned! The amplification process will be essential in this development as it will reduce the westerly vertical shear currently over the surface cold front. Thermodynamics are a disadvantage for development as this system will stay north of the 26 deg C SST isotherm. However the resulting amplification of the east US upper trough/low could lead to a large-scale upper low over the surface front whose cold temperature could allow for instability despite the mild water temps.
A non-frontal surface trough is located just north of the Dominican Republic, and marked as the potential candidate for eventual subtropical cyclone formation in the above birdseye charts. The surface trough is also supported by the upper trough/low near the eastern US. Surface convergence from this trough and 1004 mb cyclone cold front, coupled with upper divergence ahead of the upper trough/low has produced a marked increase in convective cloudiness across the central Atlantic over the last 24 hours. Expect both the surface trough and 1004 mb cyclone cold front to supply the low-level vorticity of the possible subtropical cyclone in the next days.
Southern half of Caribbean dominated by upper ridge axis supported by latent heat release of thunderstorm clouds of northern South America monsoon. Divergence from the upper ridge is allowing a surface monsoonal 1012 mb low in northern Colombia.
Central Atlantic domianted by deep-layered ridge. The upper ridge axis is the result of warm air advection ahead of the aformentioned 1004 mb cyclone frontal system. In the midst of the upper ridge is a weak shortwave upper trough in the north-central Atlantic. At the north end of the upper ridge axis is a disorganized 1006 to 1008 mb non-tropical cyclone near southern Greenland. Mass convergence east of the upper ridge axis supports a large and intense 1032 mb surface ridge anchored southwest of the Azores. The convergence east of the upper ridge axis and divergence of the 1032 mb ridge is resulting in a large swath of sinking, dry air (seen in the above thermodynamics chart) and hence stable weather across the eastern Atlantic.
Finally, the easternmost feature in the above birdseye charts is an upper trough approaching west Africa and Europe from the Cape Verde and Canary Islands. Divergence east of this upper trough supports a surface cold front currently pushing into western Europe.
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