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2013 Atlantic Hurricane Season Birdseye Discussion #26

By: NCHurricane2009 , 9:31 AM GMT on June 27, 2013

...THURSDAY JUNE 27 2013 5:30 AM EDT...
I have discontinued the pair of Caribbean tropical waves as a special feature on this blog due to the loss of thunderstorms in the south-central Caribbean Sea in addition to computer models trending toward less favorable upper winds. See paragraph P6 in the tropical belt section below for more information.

Vigorous tropical wave appears to be rolling off of Africa...and within the next 4 days will track toward favorable upper winds to develop in the open central Atlantic. However a batch of Saharan dry air detected to the west and lack of computer model support suggests no development. See paragraph P9 in the tropical belt section for more information.

As promised in my final 2012 hurricane season birdseye discussion...I have begun to release post-storm reports for the 2012 Atlantic Hurricane Season which includes evaluations of how my storm forecasts (issued on these birdseye discussions) compared with that of the official forecasts from the National Hurricane Center. As these post-storm reports come out...they can be viewed on my other blog thread at www.wunderground.com/blog/MIHurricane2009.

 photo Jun_26_2013_2345Z_CORRECTED_zps1ac1e7a5.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 2228Z-released WPC 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.

 photo Jun_26_2013_2345Z_zps28bfc408.png
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...Large frontal cyclone and upper trough is parked offshore of the west US coast...with warm air advection ahead of it producing a building upper ridge over the SW US. A slowly-developing upper trough has ejected eastward from this system and is supporting another frontal cyclone currently at 1002 mb over south-central Canada.

P2...Upper trough persists near the east Canada coast. Attendant surface frontal cyclone currently over southern Greenland has weakened from 980 to 996 mb in the last 24 hrs while the non-divergent upper trough axis shifts overhead of it (western convergence of this upper trough also supports 1018 mb ridge over Hudson Bay). Elsewhere over North America...central US upper trough has moved into eastern Canada/NE US with its eastern divergence supporting a 1005 mb frontal depression that has been quasi-stationary near the US/Canada border. Warm air advection ahead of the 1005 mb depression supports a NW Atlantic upper ridge currently centered over Bermuda.

P3...Surface troughing persists SSE of Newfoundland.

P4...Large upper vortex persists in the open central Atlantic.

P5...Surface ridge dominates much of the open Atlantic basin. Its main center...currently 1039 mb...is NE of the Azores and remains generally deep-layered in nature. The 1039 mb surface center is supported by upper convergence NE of its upper-level center. This surface ridge continues to have a westward extension currently located across the W Atlantic...SE United States...and Gulf of Mexico. This western extension is supported by upper convergence from a variety of upper features mentioned in paragraphs P1 and P2...including east side of NW Atlantic upper ridge and east side of SW US upper ridge.

P6...Pair of tropical waves continue westward across the Caribbean Sea (see above atmo chart for precise locations of both waves as of this writing). Meanwhile low-latitude upper ridging persists across much of the Atlantic tropics...but a large section of this upper ridge remains de-amplified by the paragraph P7 Bahamas-Bermuda upper vortex and paragraph P4 central Atlantic upper vortex. Upper winds over the western Caribbean Sea continue to become more favorable as the not-so-deamplified western lobe of this upper ridge merges with Florida-area upper ridge mentioned in paragraph P7...and the pinnacle of these favorable upper winds will be between now and 72 hrs...after which time the computer models have been increasingly aggressive with the paragraph P1 weather system's amplitude to the degree that they now forecast the associated upper trough to come in from the NW as squeeze out the favorable upper winds. Event the enthusiastic CMC computer model is no longer enthusiastic about developing the pair of Caribbean Sea tropical waves...and therefore these waves are no longer special features on this blog.

P7...Upper vortex remains quasi-stationary between Bermuda and the Bahamas. Upper vortex that recently migrated into the Gulf of Mexico (while orbiting around Florida-area upper ridge) is currently centered over the Bay of Campeche.

P8...Tropical wave WSW of the Cape Verde Islands in the previous discussion is now midway between the Lesser Antilles and Cape Verde Islands. It remains suppressed by the westerly vertical shear on the north side of the de-amplified portion of low-latitude upper ridging mentioned in paragraph P6 above.

P9...Satellite animation shows a supsect tropical wave along the west coast of Africa as marked in the lower-right of the above atmo chart. The wave featured an impressive t-storm cluster...and even though the t-storm cluster has fizzled for now...the shape of the remaining debris clouds suggest cyclonic turning about the wave axis. This suspect tropical wave is located below favorable eastern lobe of low-latitude upper ridging...and for the next four days models show the paragraph P4 upper vortex and pararagph P7 Bahamas-Bermuda upper vortex weakening enough to allow this low-latitude upper ridge to recover northward in the open central Atlantic as this tropical wave arrives there. Despite forecast favorable upper winds...their is a batch of dry Saharan air due west of the tropical wave (seen by brown shading in above thermo chart) apparently advected from Saharan Africa by south side of paragraph P9 1039 mb deep-layered ridge center. Moreover their is no computer model support showing development from this wave in the next 4 days...and beyond 4 days this wave may get sheared by south side of the Bahamas-Bermuda 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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