2012 Atlantic Hurricane Season Birdseye Discussion #156

By: NCHurricane2009 , 4:42 PM GMT on November 10, 2012

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...SATURDAY NOVEMBER 10 2012..11:42 AM EDT...
Subtropical cyclone development in the open eastern Atlantic now becoming less likely. See paragraph P6 for update statement on this system.

Computer models continue to agree that a surface low will develop in the western Atlantic in the timeframe that is now 84 hours. However the dynamics are not favorable for subtropical cyclone development as highlighted in paragraph P2.

Coastal weather conditions in areas hit by Hurricane Sandy days ago have vastly improved in the last 36 hours with the departure of the nor'easter as mentioned in paragraph P2.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0726Z-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 northern gale pushing across Canada's Hudson Bay in the previous discussion is entering NE Canada as a 1000 mb surface frontal low. The upper trough associated with this northern gale has merged with the north end of the upper trough in paragraph P2...with the western convergence of the upper trough supporting a 1035 mb central Canada surface ridge prior to the merger. The southern gale moving into the western US in the previous discussion is currently centered over southern Wyoming at 998 mb. Cold air from the 1035 mb ridge and moisture from the 998 mb southern gale continue to create winter weather...and winter storm warnings remain across Montana...North Dakota...and the higher elevations of the western US Rocky Mountains...with winter weather advisories across South Dakota and Nebraska. See www.nws.noaa.gov for latest info on the hazardous winter weather in these areas. Finally...low-level warm air advection ahead of the 998 mb southern gale supports a central US upper ridge. Eastern convergence of the upper ridge supports a 1026 mb eastern US surface ridge. Low-level southerlies between the 998 mb gale and 1026 mb ridge will be in directional shear with respect to upper westerlies across the central US upper ridge. The shear coupled with any instability that develops from daytime heating of land could cause severe t-storms across the central US through this weekend.

P2...Southern Greenland upper trough and associated surface gale near southern Greenland have crossed the NE Atlantic high seas while merging with the north end of the paragraph P4 upper trough. The cold front of the surface gale is marked in the upper-right corner of the above atmo chart located over western Europe. Elsewhere...the upper vortex over Massachusetts...the upper trough extending into the Caribbean...and the upper trough of the 1000 mb Hudson Bay low in paragraph P1...have all merged into one large upper trough spanning east Canada...the western Atlantic...and Caribbean. The 989 mb surface gale centered just offshore of Massachusetts in the previous discussion...a "nor'easter"...has pulled eastward further offshore in the last 36 hrs such that the weather conditions have vastly improved in coastal areas hit by Hurricane Sandy days ago. The "nor'easter" has weakened into a surface trough/cold front currently just SE of Newfoundland while it has continued to decay beneath the non-divergent axis of the upper trough. Meanwhile...eastern divergence of the upper trough has intensified the northern lobe of the dissipated nor'easter's low pressure field into a strong 974 mb gale on the east coast of Canada. Computer models agree that by 84 hours...a southern portion of the large upper trough should become cut-off...with the eastern divergence of the cut-off supporting 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...SW-NE tilted upper trough located SE of Newfoundland has become absorbed into the cut-off upper vortex of subtropical system to the southeast highlighted in paragraph P6. Deep-layered north Atlantic ridge...currently with a 1031 mb surface center...persists just SW of the Azores.

P4...Large eastern Atlantic upper trough persists. Eastern divergence of the upper trough continues supporting surface troughing over NW Africa.

...TROPICAL BELT DISCUSSION...
P5...Sprawling tropical Atlantic upper anticyclone has been split by massive paragraph P2 upper trough whose south end has amplified into the Caribbean Sea. The western split of the upper anticyclone is now an upper ridge axis over Costa Rica and the eastern Pacific. The eastern split of the upper anticyclone is now an upper ridge axis over the central tropical Atlantic. Upper divergence west of the central Atlantic upper ridge and east of the paragraph P2 upper trough supports a new surface trough over the Lesser Antilles.

P6...Cut-off upper vortex west of the Cape Verde Islands in the special feature section of previous discussion #155 has shifted NW while absorbing the SW-NE upper trough SE of Newfoundland mentioned in paragraph P3. Expansive upper divergence east of the upper vortex continues to support a large comma shaped t-storm area that has expanded into the Cape Verde Islands and eastern tropical Atlantic. This upper divergence has also intensified the associated surface trough into a 1012 mb low. Because this surface low and cloudiness is supported by a cold-core upper vortex...this system currently has the characteristics of a subtropical feature. The above-described NW shift of the upper vortex has placed the surface low in westerly vertical shear across the south side of the upper vortex...and therefore subtropical cyclone development is no longer expected from the surface low. As long as it survives...expect the surface low to continue tracking westward about the southern side of the paragraph P3 deep-layered ridge...then turn northward into the open Atlantic while influenced by the east side of forecasted W Atlantic surface low mentioned in paragraph P2.

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2. WunderAlertBot (Admin)
3:50 PM GMT on November 11, 2012
NCHurricane2009 has created a new entry.
1. wxchaser97
6:40 PM GMT on November 10, 2012
Thanks NC09!
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