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2013 Atlantic Hurricane Season Birdseye Discussion #62

By: NCHurricane2009 , 8:59 AM GMT on August 07, 2013

...WEDNESDAY AUGUST 7 2013 4:50 AM EDT...
Tropical wave crossing the Lesser Antilles appears to have produced a broad tropical low pressure currently located in its wake. This broad surface low may encounter some favorable upper winds as it moves into the Caribbean later this week...although currently none of the reliable computer models develop this system. See paragraph P8 for details. It is quiet elsewhere in the Atlantic tropics.

 photo Aug_6_2013_1945Z_zpsf77ac210.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1927Z-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 Aug_6_2013_1945Z_zps67a9fd35.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...Shortwave upper trough and attendant surface 1008 mb frontal cyclone is entering the upper-left of the above charts from central Canada.

P2...Upper trough persists over eastern Canada and northwest Atlantic. Eastern divergence of the upper trough supports the remnant low of Dorian (which has deepened to 997 mb) that has recently clipped by Newfoundland and is currently south of Greenland...as well as adjacent 1009 mb surface low over the SE Canada coast. Ex-Dorian and the 1009 mb surface low have absorbed 1008 mb surface low between Canada and Greenland mentioned in the previous discussion. A local maximum of cool air advection behind Ex-Dorian has resulted in formation of an upper vortex also located south of Greenland while warm air advection ahaed of Ex-Dorian supports persistent upper ridge over Greenland. Low-level warm air southwest of the upper trough also supports southern US upper ridge. Convergence behind the upper trough supports 1022 mb surface ridge moving offshore from the eastern US.

P3...Amplified NE Atlantic upper trough is working its way slowly into western Europe. 1009 mb surface frontal low SE of Newfoundland...mentioned in paragraph P2 of the previous discussion...is moving eastward into western Europe and has deepened to less than 1008 mb while taking advantage of eastern divergence of the upper trough.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1018 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 southern US upper ridge. The dominant open Atlantic center anchoring this ridge...currently at 1030 mb...is supported by western convergence of paragraph P3 NE Atlantic upper trough. In conjunction with south side of paragraph P7 east Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P5...Broad upper vortex persists in the vicinity of Hispaniola (Haiti and the Dominican Repbulic). Upper trough ENE of Bermuda has split into two upper troughs in advance of paragraph P2 upper trough coming in from the west.

P6...Surface troughing that was north of the Bahamas in the previous discussion...initiated by split flow upper divergence between the northerlies on the east flank of paragraph P2 southern US upper ridge and westerlies ahead of paragraph P2 upper trough...currently extends into the eastern Gulf of Mexico due to split flow upper divergence between west side of paragraph P5 upper vortex and paragraph P2 southern US upper ridge. The remainder of this surface troughing has consolidated into a 1015 mb depression in the vicinity of Bermuda located along the front extending from the remnant of Dorian.

P7..The paragraph P5 broad upper vortex continues to split low-latitude upper ridging into one upper ridge over the southern Caribbean whose outflow continues supporting an increase in thunderstorms south of Panama...and a second upper upper ridge in the eastern Atlantic featuring an embedded inverted upper trough due west of the Cape Verde Islands and embedded upper vorticity due north of the Cape Verde Islands associated with southern cut-off of NE Atlantic upper trough as mentioned in paragraph P3 of the previous discussion.

P8...Tropical wave previously apporaching the Lesser Antilles is crossing the islands into the eastern Caribbean...and expect the tropical wave to remain inactive while it is phased to slide below retrograding and suppressing upper vortex mentioned in paragraph P5. Meanwhile...in the last 48 hrs satellite animation suggested cloudiness and thunderstorms to the southeast of the tropical wave axis with some cyclonic turning...and in the last 24 hrs this area has been upgraded to a broad surface 1012 mb low presumably left behind by the tropical wave. This broad surface low will soon be crossing the Lesser Antilles and into the Caribbean Sea behind its parent tropical wave. At the same time...west end of paragraph P7 east Atlantic upper ridge extends to upper anticyclone currently just north of the Lesser Antilles...and as the paragraph P5 upper vortex and pargaraph P7 upper vorticity retrograde west...the favorable upper anticyclone located in between will also retrograde west. Despite the broad surface low and favorable upper anticyclone becoming potentially phased while moving across the Caribbean...none of the reliable computer models currently develop this system.

P9...To the southeast of embedded upper vorticity north and west of the Cape verde Islands mentioned in paragraph P7...relatively higher pressures are supporting a low-latitude upper ridge axis over the Cape verde Islands whose enhanced poleward upper outflow has supported an increase in ITCZ thunderstorms offshore of Africa and south of the islands. Due to the high activity of the ITCZ in this area...it is difficult to distinguish by satellite alone any distinct thunderstorm clusters associated with any individual tropical waves that might be rolling off of Africa...and therefore I am depending on the NHC TAFB surface maps to tell me when and where the next African tropical wave may be located. So far NHC TAFB has not added any new tropical waves rolling off of Africa.

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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