2012 Atlantic Hurricane Season Birdseye Discussion #149

By: NCHurricane2009 , 8:31 AM GMT on November 02, 2012

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...FRIDAY NOVEMBER 2 2012...4:35 AM EDT...
Tropical or subtropical cyclone formation is possible during the next 120 hours (5 days) in two areas. See paragraph P4 in the tropical belt discussion for potential tropical cyclone development in the southern Caribbean. See paragraph P2 for potential subtropical cyclone development in the open eastern Atlantic.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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 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 remnant surface low of Sandy continues weakening below non-divergent upper vortex while in SE Canada...and as of 1925Z November 1 became indistinct within a broader surface frontal low pressure. Cut-off upper trough (left behind by the upper vortex) over the SE US/Gulf of Mexico has merged with upper trough moving across the Great Lakes. Vast convergence west of the merged upper trough supports Gulf of Mexico and SW US surface ridging. Divergence on the east side of the upper vortex supports new 1000 mb frontal depression near Newfoundland...with low-level warm air advection ahead of the depression supporting an upper ridge over east Canada that was formerly the north Atlantic upper anticyclone supported by stronger warm air advection ahead of what was Sandy. Surface ridge offshore of Canada (currently 1020 mb) is becoming supported by the western convergence of the paragraph P3 upper trough.

P2...Deep-layered low pressure system/upper vortex persists in the eastern Atlantic at a location south of the Azores. Even though this system is centered over mild water temps of 23 to 24 deg C...t-storm activity persists with this system...which indicates the cold core upper vortex of the system is cold enough for instability over these water temps. 120-hour outlook of this system is complex...with the system currently trapped southeast of deep-layered ridging consisting of both the east Canada upper ridge and surface ridge offshore of Canada both mentioned in paragraph P1. As the remnant of Sandy has dissipated...the associated low-level warm air advection ahead has weakened such that the east Canada upper ridge has de-amplified...currently allowing this deep-layered low to shift east while merging with the paragraph P3 upper trough. However by the end of 120 hours...all models agree that low-level warm air advection ahead of the next frontal system will re-amplify the east Canada upper ridge...causing the paragraph P3 upper trough to re-amplify east of the upper ridge...in turn strengthening western convergence on the back side of the paragraph P3 upper trough such that the surface ridge currently offshore of Canada re-strengthens. In essence...the re-amplification of the east Canada upper ridge and strengthening surface ridge cuts-off a portion of the deep-layered low that retrogrades westward such that subtropical cyclone formation is possible once again if the current deep-layered low does not develop.

P3...Upper trough in the NE Atlantic persists in relatively lower pressures east of the the E Canada upper ridge in paragraph P1.

...TROPICAL BELT DISCUSSION...
P4...Sprawling tropical Atlantic upper anticyclone is now centered over the northern Lesser Antilles. Upper divergence on the NW quad of the upper anticyclone continues supporting central Caribbean surface troughing. T-storm activity has become less organized around the surface troughing in the last day while becoming exposed to SW vertical shear from the paragraph P1 upper troughing. This increase in shear was predicted by the GFS model yesterday...but the models soon allow the favorable tropical Atlantic upper anticyclone to rebuild over the surface trough. Although their is no computer model support for development...the potential overspreading of the favorable upper anticyclone suggests potential for tropical development. The track of this system depends on if and when development occurs. Over the next 120 hours...their will be surface ridge weaknesses that will try to draw the system east...and surface ridges that try to draw the system west. Models agree that cold fronts extending from the paragraph P1 upper troughing will first create a ridge weakness to the NE...while the Gulf surface ridge in paragraph P1 persists to the NW while supported by convergence on the back side of the paragraph P1 upper troughing. Models then eject the paragraph P1 upper trough NE...and likewise the Gulf surface ridge supported on the back side of the upper trough. Quickly...the models come in with the next frontal upper trough before 120 hours is over...with western convergence of this upper trough re-building a Gulf surface ridge to the NW...and eastern divergence of this upper trough re-creating another surface ridge weakness to the NE.

P5...Relatively higher pressures southeast of the paragraph P2 deep-layered low supports upper ridge near the Cape Verde Islands.

P6...1015 mb ridge north of the Lesser Antilles in the previous discussion is eroding while becoming exposed to upper divergence SE of the paragraph P1 upper troughing and NW of the paragraph P4 upper anticyclone. Surface ridge toward the west coast of Africa (currently 1013 mb) remains weak due to upper divergence on the SE quad of the paragraph P2 deep-layered cyclone overspreading the area.

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