2012 Atlantic Hurricane Season Birdseye Discussion #158

By: NCHurricane2009 , 12:51 AM GMT on November 13, 2012

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...MONDAY NOVEMBER 12 2012..7:51 PM EDT...
Computer models continue to agree that a surface low will develop in the western Atlantic in the timeframe that is now 24 hours. However the dynamics are not favorable for subtropical cyclone development as highlighted in paragraph P2.

A new surface trough has developed in association with an eastern Atlantic upper vortex that was previously a special feature in discussion #155. Like the previous surface trough with this system...the new surface trough could track westward into hostile upper winds while steered by the paragraph P3 deep-layered ridge. Therefore not re-upgrading the upper vortex to a special feature at this time. See paragraph P6 for update statement 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 1932Z-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).

...MID-LATITUDES DISCUSSION...
P1...The surface frontal gale centered over NW Minnesota in the previous discussion has moved rapidly NE and is currently located across Canada's southern Hudson Bay. This gale has strengthened to 988 mb from eastern divergence of large western US upper trough. Western convergence of the upper trough meanwhile supports a 1039 mb western US surface ridge. Low-level warm air advection ahead of the 988 mb gale supports an upper ridge that has moved from the central US to SE Canada/the NW Atlantic in the last 36 hrs. Eastern convergence of the upper ridge supports a surface ridge that is now 1038 mb while it has moved offshore from the eastern US/Canada into the western Atlantic.

P2...Large upper trough spanning east Canada...the western Atlantic...and Caribbean has split into two upper troughs. The northern upper trough is currently moving east across the Atlantic high seas and southern Greenland while the southern upper trough has become cut-off in the western Atlantic and Caribbean at a location south of the NW Atlantic upper ridge mentioned in paragraph P1. The intense 958 mb surface frontal gale passing by the southern tip of Greenland in the previous discussion is currently SE of Greenland while weakening to 968 mb while whirling into a position beneath the non-divergent northern upper trough axis. Expect rough seas to continue in the Atlantic high seas...and expect high winds to continue across southern Greenland and over open waters in the vicinity of this gale until the gale weakens further. Computer models agree that by 24 hours...eastern divergence of the aforementioned southern cut-off upper trough will support a W Atlantic surface low. This W Atlantic surface low will be exposed to high SW vertical shear as the cut-off never closes off into an upper vortex...and the surface low will track northward quickly into cooler waters below 26 deg C. Therefore...this forecast surface low is not expected to develop into a subtropical cyclone.

P3...Deep-layered north Atlantic ridge...currently with a 1027 mb surface center...persists now at a location just east of the Azores.

P4...Upper trough/surface cold front moving into western Europe in the previous discussion has exited the scope of the above charts from the upper-right corner.

...TROPICAL BELT DISCUSSION...
P5...Upper ridge axis over the central tropical Atlantic persists. Upper divergence west of this upper ridge and east of the cut-off southern paragraph P2 upper trough supports a surface trough that has moved westward from the Lesser Antilles into the eastern Caribbean. The surface trough has been steered westward by the 1038 mb western Atlantic surface ridge mentioned in paragraph P1.

P6...Cut-off upper vortex NW of the Cape Verde Islands persists. Expansive upper divergence east of the upper vortex continues to support a large comma shaped t-storm area that continues overspreading the Cape Verde Islands and eastern tropical Atlantic. A new surface trough has developed in the last 24 hrs while supported by the same upper divergence. Elsewhere...the previous and old surface trough that was spawned in the upper divergence...located midway between the Cape Verde Islands and Lesser Antilles as of the previous discussion...has continued to track westward while steered by the 1027 mb ridge in paragraph P3. On this continued track...this old surface trough has continued across the south side of the upper vortex where westerly vertical shear is inhibiting it. It is also suppressed by dry sinking air supported by the western convergence of the upper vortex.

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