2012 Atlantic Hurricane Season Birdseye Discussion #167
...FRIDAY NOVEMBER 23 2012...1:39 PM EDT...
Shortly after the previous discussion was written...western Atlantic surface low had lost organized t-storm activity...but this early afternoon has regained t-storm activity while centered just north of Bermuda. Summary of how this feature has evolved in the last 24 hours is described in paragraph P2 below. Today is the final day for any potential subtropical cyclone development before the surface low hooks sharply northward toward cooler waters and into Atlantic Canada in the next 48 hours while the surface low gets steered by southeast half of the paragraph P1 upper trough/surface frontal system. However...such subtropical development appears unlikely as this system still lacks decent t-storm activity close to the center and continues to be analyzed with a non-tropical surface cold front in National Hurricane Center TAFB surface maps.
With one week left in the 2012 Atlantic Hurricane Season...will be looking at computer model runs tonight to assess what the large-scale weather pattern looks like for the remainder of hurricane season. If the forecast pattern does not appear conducive for anymore subtropical or tropical cyclone development...will write a special update declaring the end of my daily full birdseye discussions for the 2012 season.
...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 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...Western US upper trough in the previous discussion has entered the central US. Eastern divergence of the upper trough supports surface frontal depression that has intensified from 999 to 992 mb over the last 24 hrs. This surface frontal depression has moved from north-central Minnesota to Lake Superior during this time. Western convergence of the upper trough supports strong 1039 mb surface ridge building into the western US. Strong northerly cold winds blowing over the warmer Great Lakes...generated between the 1039 mb ridge and 992 mb depression...will promote lake effect snow in the Great Lakes region during the next 24 hours.
P2...Broad 1004 to 1008 mb surface low offshore of the SE US in the previous discussion has intensified to 997 mb while moving ENE and passing just north of Bermuda. Intensification was supported by eastern divergence of associated cut-off upper trough. Upper vortex at north end of the cut-off upper trough has aligned with the surface 997 mb center...resulting in a deep-layered low. Upper convergence behind (west) of the deep-layered low supports 1024 mb surface ridging across the SE US...Gulf of Mexico...and Nw Caribbean.
P3...NE Atlantic upper trough in paragraph P3 of the previous discussion...east Canada upper trough in paragraph P2 of the previous discussion...and Azores upper trough in paragraph P3 of the previous discusion...have all merged into one large NE Atlantic upper trough. Less-than-1004 mb surface low crossing the Azores in paragraph P3 of the previous discussion is continuing ENE toward Europe while supported by the eastern divergence of this large NE Atlantic upper trough. Marine 994 mb surface frontal depression just SW of Greenland in paragraph P2 of the previous discussion is moving east by the south tip of Greenland...and should soon weaken beneath the western convergence of the NE Atlantic upper trough. Greater-than-1020 mb surface ridge offshore of Atlantic Canada is supported by this upper convergence. 1025 mb surface ridge just north of the Canary Islands in paragraph P3 of the previous discussion is breaking up into a 1018 to 1024 mb ridge covering the east half of the above atmo chart while this ridge erodes in advance of less-than-1004 mb surface low heading toward Europe.
...TROPICAL BELT DISCUSSION...
P4...Upper ridge over the central tropical Atlantic persists. Upper divergence west of this upper ridge supports scattered t-storm activity across the central Caribbean Sea.
P5...Cut-off upper trough W of the Cape Verde Islands persists...but continues to be squished out by growth of paragraph P4 upper ridge (this upper ridge is growing thanks to low-level warm air advection ahead of paragraph P2 997 mb deep-layered low). What is left of surface troughing formerly supported by eastern divergence of this cut-off upper trough is SE of the Lesser Antilles. This surface troughing continues to be steered west by the 1018 to 1024 mb ridge mentioned in paragraph P3 above.