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2012 Atlantic Hurricane Season Birdseye Discussion #21
By: NCHurricane2009 , 3:50 AM GMT on June 06, 2012
...JUNE 5 2012...11:55 PM EDT...
After the unusual pre-season tropical activity in the Atlantic...no signs of new tropical activity as the Atlantic Hurricane Season officially starts. What caused the early activity...followed by an outlook of potential activity in the next several days...will be discussed here in the next day or two.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-released HPC analysis.
In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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 in mid-latitudes is entering the picture from the upper-left of the above birdseye charts...over the western US. Divergence east of this upper trough supports a surface frontal cyclone over Montana. Warm air advection ahead of this Montana cyclone supports an upper ridge from western Texas to the Manitoba province of Canada. Upper westerlies across the upper ridge axis...coupled with low-level southerlies ahead of the Montana cyclone..is allowing for directional wind shear favoring severe T-storms and tornadoes in Montana tonight.
P2...Over the eastern US...there has been a longwave upper trough regime with embedded shortwaves swinging through. This longwave upper trough regime contains the remnants of the frontal system in paragraph P1 of discussion #20. Tonight...the longwave upper trough regime consists of a SW-NE-tilted upper trough and upper vortex near Atlantic Canada (cut-off to the SW of paragraph P4 upper anticyclone). Divergence ahead of the SW-NE upper trough supports a stalled front over the southern tier of the US that extends to a 998 mb cyclone offshore of Atlantic Canada. Convergence behind the SW-NE upper trough (with respect to paragraph P4 upper anticyclone) supports a 1021 mb Michigan ridge and 1030 mb ridge near the east coast of Canada.
P3...See paragraph P3 of previous discussion #20 for longwave upper trough regime across the entire high seas of the Atlantic. This longwave upper trough still has an upper low vortex at its north end while cut-off to the south of the upper anticyclone in paragraph P4. At the surface...dominant feature is decaying cyclone south of Greenland currently at 1001 mb (1330Z HPC) that once was 988 mb in discussion #20. Other features of this regime include an upper trough across the Lesser Antilles...another upper trough midway between the Antilles and Azores...and a third upper trough over the Canary Islands. Subtropical surface ridging several days ago was supported by upper anticyclone in paragraph P4. This surface ridging is regaining intensity tonight...as a 1027 mb center supported by convergence W of the Canary Islands upper trough.
P4...Full-fledged and anomalous upper anticyclone west of the British Isles is centered over S Greenland tonight.
...TROPICAL BELT DISCUSSION...
P5...Long-lived Caribbean upper ridging persists. There is an accelerationally-divergent upper westerly jet north of this ridge and south of the regime in paragraph P2...the divergent aspect allowing for t-storms across the Gulf of Mexico. The strong westerly aspect is also causing very high vertical shear unsuited for tropical development with these t-storms.
P6...Tropical wave in paragraph P7 of discussion #20...which was nearing the Lesser Antilles...has dissipated and has been removed from the NHC TAFB analyses days ago.
P7...Upper ridge in E tropical Atlantic has expanded westward toward the Lesser Antilles...the expansion caused by the weakening of adjacent upper trough regime in paragraph P3. Animation of thermodynamics birdseye charts (such as the above) since June 1 suggests a westward expansion of dry air from western Africa...supported by deep-layered easterly flow south of the 1027 mb ridge (paragraph P3)...and south of the E Atlantic upper ridge (mentioned in this paragraph).
P8...A tropical wave approaching the Lesser Antilles is at the west end of paragraph P7 upper ridge...where it has found enhanced poleward outflow and hence why it has seen an increase in t-storms. However...this tropical wave will soon encounter hostile southerly vertical shear from the Lesser Antilles upper trough (mentioned in paragraph P3).
P9...A tropical wave is S of the Cape Verde Islands and towards the east end of paragraph P7 upper ridge. This tropical wave is suppressed by dry air mentioned in paragraph P7.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.