2012 Atlantic Hurricane Season Birdseye Discussion #137

By: NCHurricane2009 , 11:04 AM GMT on October 19, 2012

...FRIDAY OCTOBER 19 2012...7:10 AM EDT...
Although the Atlantic tropics are currently calm....their is increasing computer model support for tropical cyclogenesis in the Caribbean Sea by 120 hours. See paragraph P5 for statement on this situation.

GOES-E satellite has finally been repaired. Therefore...the view in the two birdseye charts below no longer requires repair.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0731Z-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...Surface frontal system in the mid-latitude westerlies continues marching eastward across North America with a pair of upper troughs. The first upper trough with embedded upper vortex has arrived into the central US. 983 mb cyclone over NW Minnesota in the previous discussion has whirled SE into a position beneath the upper vortex...resulting in a 994 mb deep-layered cyclone centered over Wisconsin this morning. Strong convergence on the west side of the deep-layered cyclone supports building surface ridge across the western US with 1024 mb to 1016 mb centers. Upper ridge persists across SE Mexico in relatively higher pressures south of the deep-layered cyclone. Secondary upper trough of this system has moved from the eastern US into the W Atlantic in the last 24 hrs..its western convergence supporting 1025 to 1024 mb ridge over the NW Atlantic and SE Canada.

P2...Upper trough and surface frontal system over the western Atlantic in the previous discussion has advanced ENE into the north Atlantic high seas in the vicinity of southern Greenland. Western convergence of the upper trough formerly supported a surface ridge over E Canada...but now this ridge is supported by western convergence of secondary upper trough in paragraph P1. However...eastern divergence of this upper trough continues supporting a strong surface frontal depression that has intensified from 989 mb to 977 mb while moving ENE past this southern tip of Greenland in the last 24 hours. Surface cold front of this depression continues to have the remnant gale of Rafael also racing ENE across the north Atlantic high seas. Eastern divergence of this upper trough also supports the remnant of Rafael...so expect Rafael to continue its slow rate of weakening. Rafael may soon lose its identity if it merges with aforementioned 977 mb center. Cold front in which Rafael is embedded extends far to the southwest...and in the last 48 hours has left behind surface troughs over the western Caribbean and near western Cuba....as well as another surface trough ENE of Bermuda. The surface trough ENE of Bermuda is currently supported by eastern divergence of secondary upper trough mentioned in paragraph P1.

P3...Upper trough continues eastward across the NE Atlantic and is making landfall in western Europe this morning. Western convergence of the upper trough formerly supported what is now the 1024 mb surface ridge in the eastern Atlantic...but this surface ridge is now stacked with upper ridge mentioned in paragraph P4 to make a deep-layered ridge. Meanwhile...eastern divergence of this upper trough supports a surface low and associated cold front continuing to advance eastward across western Europe and Morocco.

P4...Large-sized central Atlantic upper ridge extending into the eastern Caribbean has split into two this morning. One center is vertically stacked with 1024 mb east Atlantic surface ridge in paragraph P3...resulting in a deep-layered ridge. The other center remains in the eastern Caribbean just south of Hispaniola (Haiti and the Dominican Republic).

P5...Tropical wave crossing the southern Lesser Antilles in paragraph P5 of previous discussion #136 is now in the eastern Caribbean. Along with upper outflow enhancement from paragraph P4 upper ridge center south of Hispaniola...the tropical wave is producing scattered t-storm clouds across the eastern Caribbean Sea this morning. By 120 hours...computer models agree that a broad tropical low or tropical cyclone will spin up in the central Caribbean region. Not sure at this time if it is this tropical wave that the models are developing. If not...perhaps it is the tropical wave in paragraph P6...which will travel westward and eventually also interact with the favorable upper ridge center south of Hispaniola.

P6...In the tropical Atlantic east of the Lesser Antilles...cut-off upper vortex persists. Western of the two tropical waves in the vicinity has escaped the influence of the upper vortex...and has its own paragraph (see paragraph P5 above). The eastern of the two tropical waves is producing enhanced t-storm activity while interacting with the eastern divergence of the upper vortex. However...this t-storm cluster is sheared off the wave by the upper westerly winds across the south side of the upper vortex. Meanwhile...E tropical Atlc upper ridge persists in relatively higher pressures E of the upper vortex.

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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