2012 Atlantic Hurricane Season Birdseye Discussion #76

By: NCHurricane2009 , 11:57 PM GMT on August 11, 2012

...AUGUST 11 2012...8:05 PM EDT...
Atlantic tropics have rapidly quieted in last 36 hours. For info on the remnants of Florence...remnants of tropical depression seven...and strong tropical wave Invest 93-L...see paragraphs P7 thru P9 in tropical belt discussion.


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.


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...Upper trough regime over central US and central Canada has spread into eastern areas and Atlantic high seas. Frontal cyclone that crossed Greenland in previous discussion leaves behind front over north Atlantic with a 1008 mb cyclone SE of Greeland. Local cool air advection behind this 1008 mb cyclone has generated a shortwave upper trough whose western convergence supports 1022 mb ridge centers E of Newfoundland. Intensifying frontal cyclone headed toward eastern Great Lakes has become stationary while its cool air advection has caused an upper vortex to develop overhead of itself. With the upper vortex overhead...this Great Lakes cyclone is now deep-layered and at 1005 mb as of 1200Z earlier today. Central North America surface ridge is re-building with support of upper convergence on back side of this upper trough regime...as seen with 1020 to 1023 mb centers in upper-left corner of above atmo birdseye chart stretching from the SW US to eastern Canada. Low-level warm air advection ahead of Great Lakes cyclone supports W Atlantic upper ridge...while SW US upper ridge persists behind this upper trough regime.

P2...Deep-layered vortex north of the Azores is shifting east into western Europe...and its upper vortex has de-amplified into a NE Atlantic upper trough.

P3...Mid-ocean upper vorticity persists....now featuring a few upper vortex centers. One upper vortex is moving NW from W Caribbean and into E Gulf of Mexico. A second and quiet large upper vortex is digging southwestward around the W Atlantic upper ridge (paragraph P1)...now reaching the eastern Caribbean Sea. A third upper vortex shows faintly in the above atmo chart 200 mb wind barbs...located SSW of the Azores.

P4...Atlantic surface ridge with 1022 mb to 1026 mb centers is supported by a few upper convergent sources while stretching from W Atlantic to waters offshore of W Europe....including convergence SE of the of west Atlantic upper ridge (paragraphs P1)...and convergence behind NE Atlantic upper trough (paragraph P2). In conjunction with south side of W Atlantic upper ridge (paragraph P1)...south side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.

P5...Upper ridging across Atlantic tropics has re-structured in last 36 hrs. An upper ridge is developing in the central Caribbean as a southward extension of W Atlantic upper ridge in paragraph P1...and is supported by relatively higher pressures between the W Caribbean upper vortex and E Caribbean upper vorticity mentioned in paragraph P3. Tropical upper ridging remains firmly established in eastern tropical Atlantic.

P6...Tropical wave in central Caribbean during the previous discussion has rapidly moved westward into Central America and now into SE Mexico/Bay of Campeche. Westerly shear from the W Caribbean/E Gulf of Mexico upper vortex (paragraph P3) has separated all t-storm activity from this tropical wave. This t-storm activity...currently in the western Caribbean...remains supported by split flow divergence between this upper vortex and new upper ridging developing in the central Caribbean Sea (paragraph P5).

P7...Remnants of Florence is currently located just north of the Bahamas. Remnants are shown in NHC TAFB maps as an increasingly weaker surface trough tracking WNW toward deep-layered ridge weakness associated with east Great Lakes deep-layered cyclone in paragraph P1. Despite being under favorable W Atlantic upper ridge (also in paragraph P1)...remnants of Florence not showing signs of regeneration...so I no longer have this as a special feature on this blog. I expect the remnants to either dissipate...or to continue curving more northward in track such that it passes east of the US shoreline and west of Bermuda...perhaps merging with cold front of Great Lakes cyclone expected to push into the Atlantic.

P8...Tropical depression seven has collapsed into a remnant low/tropical wave in last 36 hrs due to excessive rapid westward motion. See recent discussion #72 Ernesto section on how rapid westward motion can dissipate a weak tropical cyclone. Low-level cloud motions in visible satellite...and rapid motion of tropical wave in paragraph P6...suggest the remnants of seven will continue rapidly westward as it crosses the Lesser Antilles tonight and across the Caribbean Sea in the next days. In addition (as previous TD 7 discussion highlighted)...remnant of seven is beginning to encounter unfavorable southwesterly shear from paragraph P3 upper vorticity retrograding into the Caribbean Sea. The only thing going for TD 7 to regenerate is that its rapid westward motion could allow it to outrun the paragraph P3 upper vorticity and into more favorable paragraph P5 central Caribbean upper ridge. Then again...east side of this Caribbean upper ridge could promote upper convergence (like a typical mid-latitude upper ridge wave)...which would strengthen the dry air to Seven's northwest and go against its regeneration (source of dry air mentioned in paragraph P4).

P9...Strong tropical wave Invest 93-L has crossed the Cape Verde Islands...and its large low pressure spin is now centered just NW of those islands. Its t-storm activity has reduced due to unfavorable thermodynamics...namely ingestion of dry air to its northwest and having its north side cross over waters below 26 deg C. While it is currently under favorable upper outflow beneath paragraph P5 upper ridge...and its westward track will take it to increasingly warm waters...I have stopped considering this a special feature on this blog until I see how well it fares against its recent dry air ingestion (source of this dry air mentioned in paragraph P4).

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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