2012 Atlantic Hurricane Season Birdseye Discussion #154

By: NCHurricane2009 , 10:31 AM GMT on November 08, 2012

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...THURSDAY NOVEMBER 8 2012..5:30 AM EDT...
Slight chance of subtropical cyclone development in the open eastern Atlantic remains possible as highlighted in paragraph P4 of the mid-latitudes discussion.

See paragraph P2 in the mid-latitudes discussion for statement on what is a strong nor'easter impacting the same coastal areas in the northeastern United States hit by last week's Hurricane Sandy.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1920Z-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...Eastern lobe of gale offshore of the west coast of North America has crossed the US and has merged with nor'easter mentioned in paragraph P2. The associated shortwave upper trough...currently over central Canada...is merging and re-enforcing the paragraph P2 upper trough. Remaining west lobe of the gale has moved onshore into the western US and western Canada and is entering the upper-left corner of the above charts. Currently...warm air advection ahead of the gale supports west coast upper ridge that has shifted into the western US. Eastern convergence of the upper ridge supports a 1022 to 1023 mb central US surface ridge.

P2...Large-scale upper trough over the eastern US in the previous discussion currently consists of an upper vortex that has de-amplified into an upper trough while moving from the Maine/Canada border to southern Greenland. It also consists of an upper vortex over western North Carolina that has moved into NE North Carolina...as well as a shortwave upper trough over the southern Gulf of Mexico and Yucatan Peninsula. In the last 24 hours...eastern divergence of the southern Greenland upper trough has intensified the 994 mb Newfoundland surface frontal depression into 988 mb while moving NNE past the southern tip of Greenland. Western convergence of this upper trough supports 1029 mb east Canada surface ridge. Strong divergence on the east side of the NE North Carolina upper vortex has supported the rapid genesis of a surface non-tropical gale offshore of the US and along the front extending from what is now the 988 mb depression. This strong gale had already intensified to 996 mb as of last evening while tracking NE parallel to the US coast...and therefore it is called a "nor'easter." Unfortunately...the nor'easter is currently impacting coastal areas hit by last week's Hurricane Sandy with gusty winds and snow.

P3...Large upper trough pushing into the western Atlantic remains split into two SW-NE tilted upper troughs...one east of Greenland that has recently merged with the paragraph P4 upper trough...and the second remaining in the open central Atlantic located SE of Newfoundland whose south end now has an upper vortex. Relatively higher pressures between both upper troughs is currently where the north Atlantic upper ridge in the previous discussion thrives. Finally...the north Atlantic surface ridge (currently 1033 mb) remains supported by western convergence of the paragraph P4 upper trough.

P4...Large eastern Atlantic upper trough persists. Surface 1013 mb frontal depression over Morocco supported by the eastern divergence of this upper trough is now a 1015 mb depression near southern Portugal and a surface trough over Morocco. Low-level warm air advection ahead of what is a nor'easter mentioned in paragraph P2 will keep the north Atlantic upper ridge mentioned in paragraph P3 amplified...which has fractured the south end of this upper trough at a location W of the Cape Verde Islands. Upper westerlies flowing across this southern fracture heavily diverge with easterlies flowing into the paragraph P3 upper vortex...resulting in an impressive area of t-storms W of the Cape Verde Islands. This cluster of t-storms is also supported by the eastern upper divergence of this southern fracture. Upper divergence in split northerly flow between this southern fracture and east end of the paragraph P5 upper anticyclone supports a new surface trough midway between the Cape Verde Islands and Lesser Antilles. Computer model runs such as the CMC...GFS...and NOGAPS from last evening suggested the formation of a potential surface subtropical cyclone beginning in the 80 to 96 hr timeframe supported by eastern divergence of this southern fracture.

...TROPICAL BELT DISCUSSION...
P5...Sprawling tropical Atlantic upper anticyclone continues covering the waters just east of the Lesser Antilles and the Caribbean Sea. As seen in the above thermo chart...dry air continues to whirling within the upper anticyclone...perhaps supported by converging upper northeasterlies on the SE half of the upper anticyclone. In the last 24 hours...their has been an increase in south-central Caribbean t-storms supported by the outflow of the upper anticyclone.

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