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2013 Atlantic Hurricane Season Birdseye Discussion #34

By: NCHurricane2009 , 5:26 AM GMT on July 06, 2013

...SATURDAY JULY 6 2013 1:26 AM EDT...
Although computer model support for western Gulf of Mexico development has diminshed...the area of disturbed weather in this region has been upgraded to Invest 94-L by the Naval Research Laboratory of the United States Navy. See paragraph P5 for update statement on this situation.

Elsewhere...the south end of a tropical wave west of the Cape Verde Islands has quickly become organized in the last 24 hours. Although their is no computer model support for development...upper winds could be favorable for much of the next five days. Therefore I will upgrade this tropical wave to a special feature if it continues to stay organized in the next 24 hours. See paragraph P10 for details.

 photo Jul_5_2013_1745Z_zps44d1f6b5.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1919Z-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 Jul_5_2013_1745Z_zps6185c420.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...Frontal cyclone and attendant upper trough SE of Greenland had exited the picture from the upper right of the above charts...but the upper trough leaves behind a cut-off SE of Newfoundland. 1010 mb frontal depression forming SE of Newfoundland in the previous discussion has moved NE and is currently 1012 mb while supported by eastern divergence of the cut-off upper trough. A new 1013 mb non-frontal surface depression has also developed well ENE of Bermuda while supported by split flow upper divergence at the boundary between the cut-off upper trough and NW Atlantic upper ridge mentioned later in this paragraph. Remainder of upper troughing from this system remains cut-off over the central US...with eastern divergence of this cut-off formerly supporting an eastern US frontal system that is now dissipating. NW Atlantic upper ridge was formerly supported by warm air advection ahead of what is now this dissipating surface front...but is now supported by warm air advection on the west side of the low-level ridge mentioned in paragraph P4.

P2...Upper trough and surface frontal cyclone previously in the high seas between Canada and Greenland is now SE of Greenland while its surface center has rapidly deepened to 978 mb in the last 36 hrs (this upper trough has temporarily merged with cut-off upper trough SE of Newfoundland mentioned in paragraph P1). Another upper trough and surface frontal system from northern Canada is currently crossing Hudson Bay with a 996 mb surface center over the northeast part of the bay.

P3...Upper vortex NE of the Lesser Antilles is beginning to retrograde westward around the paragraph P1 NW Atlantic upper ridge. Split northeasterly flow between the NW quad of this upper vortex ans SE quad of the NW Atlantic paragraph P1 upper ridge supported a flare up of t-storms last afternoon which has since wrapped cyclonically beneath the upper vortex and is now weakened this evening.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1028 mb center now midway between North Carolina and Bermuda has whirled anticylonically into a position beneath the center of the paragraph P1 NW Atlantic upper ridge...which effectively makes this a deep-layered ridge center at this time. An eastern greater-than-1028 mb center near western Europe is supported by northeastern convergence of the eastern Atlantic upper ridge mentioned in paragraph P7.

P5...As the statements in paragraph P1 above confirm...in the last days the south half of what was a large eastern North America upper trough has fractured into a central US upper trough...and this upper trough has begun weakening which has allowed the favorable tropical upper ridging to the south to expand northward and support active tropical weather in the western Gulf of Mexico. However...paragraph P6 upper vorticity has retrograded westward toward the eastern Gulf...squeezing the favorable tropical upper ridging between that upper vorticity and the central US upper trough. Moreover...the surface troughing (which has recently developed a 1011 mb low) remains supported by by eastern divergence of the central US upper trough...which places the lowest surface pressures in unfavorable southwesterly vertical shear ahead of the upper trough. After 36 hrs from now...models show upper winds becoming more favorable with the paragraph P6 upper vorticity dissipated and the remainder of the paragraph P1 central US upper trough a weakened TX/MX upper vortex that perhaps could make a more subtropical rather than a fully tropical situation. Despite the recent upgrade to Invest 94-L and continued mention of this disturbed weather in the NHC Tropical Weather Outlook...Will not consider this a special feature on this blog until the system shows some signs of organization. As previously stated in paragraph P5 discussion #33...any tropical system that develops out of this would track NNW around the west side of the paragraph P4 ridge and into the Texas or east-facing Mexico coast as the eastern divergence of the paragraph P1 central US upper trough prevents the paragraph P4 ridge from re-building in the Gulf region.

P6...Upper vortex previously over the central Bahamas has retrograded westward about the paragraph P1 NW Atlantic upper ridge...and is currently over the east Florida coast and Cuba while weakening into an inverted upper trough. Another inverted upper trough has formed in the central Caribbean in relatively lower pressures southeast of the tropical upper ridging mentioned in paragraph P5.

P7...Anticyclonic upper ridging in the eastern half of the Atlantic persists. It still has an upper anticyclone west of Portugal/Europe now supported by warm air advection ahead of the 978 mb cyclone mentioned in paragraph P2 (and this upper anticyclonicity has a long...albeit somewhat broken...extension hundreds of miles southwestward toward the Lesser Antilles)...with relatively lower pressures south of the Portugal anticyclone supporting a SW-NE oriented series of upper vorticity features from the Canary Islands to the waters NW of the Cape Verde Islands. To the southeast of the upper vorticity is a low-latitude upper ridge over the Cape Verde Islands extending into W Africa.

P8...Tropical wave previously in the Mona Passage (midway between Puerto Rico and the Dominican Republic) is now in the south-central Caribbean heading into Central America. It is currently suppressed by dry Saharan air (seen by brown shading in lower part of above thermo chart) earlier advected from Saharan Africa by deep-layered easterly wind current on the south side of the paragraph P7 upper ridge and paragraph P4 surface ridge. The patch of dry air in the vicinity of this tropical wave in particular is currently supported by southeastern convergnce of the paragraph P5 tropical upper ridging.

P9...Tropical wave midway between the Cape Verde Islands and Lesser Antilles has made a defenite re-surgence in moisture against the dry air mentioned in paragraph P8 thanks to enhanced upper outflow of the paragraph P7 upper ridging supporting lift over the ocean surface.

P10...Tropical wave previously over the Cape Verde Islands is now west of the islands. It appears the south end of the tropical wave has rapidly organized into an active 1011 mb surface low pressure spin perhaps while taking advantage of the low shear and enhanced outflow of the paragraph P7 upper ridging. This has caused the NHC to introduce the tropical wave into its outlook this evening. I will assume the enhanced outflow of the paragraph P7 upper ridging will continue to trigger enough moistening lift over the ocean surface as to ward off the dry air mentioned in paragraph P8. Therefore it will be upper winds that will control the fate of the tropical wave...and based on the latest GFS model run this tropical wave will be below the favorable paragraph P7 tropical upper riding for the next 5 days (120 hrs) as it moves toward the Lesser Antilles (albeit the wave may encounter some of the less favorable paragraph P7 upper vorticity in the 24 to 48 hr timeframe after which time this upper vorticity diminshes). Therefore if this tropical wave conitnues to display an organized low pressure spin...I will be upgrading it to a special feature on my next blog post.

P11...During the previous discussion...Meteosat-9 satellite animation appeared to suggest the most impressive tropical wave of the season thus far was rolling off of Africa. This evening...it appears the dominance in this region now goes to the tropical wave mentioned in paragraph P10 while this suspect tropical wave has rapidly lost most of its activity. However I have marked this suspect tropical wave at a location SE of the Cape Verde Islands for the sake of continuity from my previous discussion...but if this suspect wave is not added in future NHC TAFB surface maps I will drop it from this blog.

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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