2012 Atlantic Hurricane Season Birdseye Discussion #150
...SATURDAY NOVEMBER 3 2012...11:30 AM EDT...
Tropical or subtropical cyclone formation is possible during the next days in two areas. See paragraph P4 in the tropical belt discussion for potential tropical cyclone development in the southern Caribbean. See paragraph P3 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 0600Z, and the 0725Z-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).
P1...Next upper trough and surface frontal system in the mid-latitudes has entered the picture from the western US. The upper trough consists of an upper vortex over the Dakotas and upper trough over the SW US...and the surface frontal system consists of 1010 mb depressions in the Texas/Oklahoma area as well as a 1020 mb depression over South Dakota. Relatively warmer air ahead of these surface depressions supports a low-amplitude shortwave upper ridge over the central US.
P2...Broad surface frontal low in which Sandy became indistinct within during the previous discussion has lifted northward from SE Canada and out of the scope of the above birdseye charts. Meanwhile...upper vortex above this broad surface low has shifted eastward while merging with Great Lakes-to-Gulf of Mexico upper trough now heading into the western Atlantic. Vast convergence west of the upper trough/vortex supports a 1021 mb ridge in the Gulf of Mexico and 1028 mb ridge diving SE from central Canada. Divergence on the east side of the upper trough/vortex supports 1000 mb frontal depression near Newfoundland in the previous discussion...which has lifted northward into SE Canada while intensifying into 996 mb. This same upper divergence also supports new 996 to 997 mb surface frontal depressions just south of Atlantic Canada. Low-level warm air advection ahead of these frontal depressions are supporting an upper ridge over the east coast of Canada. Surface ridge offshore of Canada (currently 1025 mb) is becoming supported by the western convergence of the paragraph P3 upper trough.
P3...Upper vortex of deep-layered east Atlantic low south of the Azores is merging with NE Atlantic upper trough from paragraph P2 of the previous discussion to create one large upper trough across all latitudes of the eastern Atlantic. Meanwhile...the surface vortex of the former deep-layered low has weakened to 1000 mb while exposed to the non-divergent upper trough axis. Upper divergence east of this axis meanwhile supports a 1004 mb frontal depression moving into NW Spain...located along warm front extending from the 1000 mb low. Models over the last couple of days have shown that low-level warm air advection ahead of the paragraph P1 frontal system will re-amplify the paragraph P2 east Canada upper ridge...causing the aforementioned east Atlantic upper trough to re-amplify east of the upper ridge axis...in turn strengthening western convergence on the back side of the upper trough axis such that the surface ridge currently offshore of Canada (mentioned in paragraph P2) re-strengthens. In essence...the re-amplification of the east Canada upper ridge and strengthening surface ridge cuts-off a portion of the aforementioned 1000 mb low and east Atlantic upper trough that all retrogrades westward such that subtropical cyclone formation is possible.
...TROPICAL BELT DISCUSSION...
P4...Sprawling tropical Atlantic upper anticyclone now has one anticyclonic center east of the Lesser Antilles and another over the Caribbean Sea. T-storm activity has dwindled in association with the surface troughing in the central Caribbean Sea in the last 36 hrs. However because the upper anticyclone now overspreads the central Caribbean surface trough...this area will need to be monitored for potential tropical development. The track of this system depends on if and when development occurs...with ridge weaknesses to the NE favoring a more NE track...and surface ridges to the NW favoring a westward track. Cold fronts extending from the paragraph P2 upper troughing have created a ridge weakness to the NE...while the Gulf surface ridge in paragraph P2 persists to the NW while supported by convergence on the back side of the paragraph P2 upper troughing. Models then eject the paragraph P2 upper trough NE...and likewise the Gulf surface ridge supported on the back side of the upper trough. Quickly...the models eject the paragraph P1 upper trough eastward in place of the paragraph P2 upper trough such that its western convergence re-builds a Gulf surface ridge to the NW...and eastern divergence of this upper trough re-creates another surface ridge weakness to the NE.
P5...Relatively higher pressures southeast of the paragraph P3 upper trough supports upper ridge near the Cape Verde Islands.
P6...Surface ridge toward the west coast of Africa (currently 1015 to 1017 mb) remains weak due to upper divergence on the east of the paragraph P3 upper trough overspreading the area.