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2013 Atlantic Hurricane Season Birdseye Discussion #35

By: NCHurricane2009 , 3:11 AM GMT on July 07, 2013

...SATURDAY JULY 6 2013 11:11 PM EDT...
Disturbance Invest 94-L in the western Gulf of Mexico continues to lack organization. See paragraph P5 for update statement on this system.

The south end of the tropical wave west of the Cape Verde Islands continues to stay organized and has been upgraded to disturbance Invest 95-L. With upper winds forecast to remain favorable for additional development....I have upgraded this tropical wave to a special feature on this blog due to high risk of tropical cyclone development at anytime within the next few days. See special feature section below for additional details on this situation.

 photo Jul_6_2013_1815Z_zps5c1d72c1.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1915Z-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_6_2013_1815Z_zpsac4eb5c7.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).

Tropical wave west of the Cape Verde Islands continues west into the waters midway between the Cape Verdes and Lesser Antilles. In the last two days...the south end of the tropical wave has organized into an active 1009 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 since yesterday evening and has caused the Naval Research Laboratory of the United States Navy to designate the tropical wave as disturbance Invest 95-L.

I will continue to assume that the tropical wave will not choke on Saharan dry air while embedded in the moisture resurgence toward Africa mentioned in the latter part of paragraph P7. 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 ridging for the next few days...especially as the embedded upper vorticity features also mentioned in paragraph P7 are shown to dissipate and as the upper ridging expands into the Caribbean in the wake of the retrograding paragraph P3 upper vortex. No computer models currently develop this tropical wave except the CMC which develops it into a tropical cyclone when it reaches the Caribbean/Gulf of Mexico region by 180 hrs (of course such long range solutions cannot be fully trusted). Expect the tropical wave to continue westward while steered by solid paragraph P4 surface ridge...and with the organization of the low pressure spin suggesting possible tropical cyclone formation at anytime within the next days...the Lesser Antilles should monitor the progress of this tropical wave.

P1...Cut-off upper trough and surface frontal cyclone (currently 1013 mb) SE of Newfoundland is moving eastward toward the Azores. Remainder of upper troughing from this system remains cut-off over the central US in between NW Atlantic upper ridge and western US upper ridge.

P2...Upper trough and strong surface frontal cyclone previously SE of Greenland has mostly exited the picture from the upper-right of the above charts. Part of this upper trough remains over Greenland and far north Atlantic...with eastern divergence of this upper trough portion supporting a new 1000 mb depression south of Greenland along the front extending from the exited strong cyclone. Another upper trough and surface frontal system from northern Canada is currently crossing Hudson Bay with a 998 mb surface center over the northeast part of the bay.

P3...Upper vortex previously NE of the Lesser Antilles has retrograded westward to a position north of Puerto Rico while steered around the paragraph P1 NW Atlnatic upper ridge. Split easterly flow between the NW quad of this upper vortex and south half of the NW Atlantic paragraph P1 upper ridge supports a new surface trough near the eastern Bahamas with some cloud activity. CMC computer model suggests development of a subtropical or tropical cyclone from this surface trough/upper vortex when the system retrogrades into the eastern Gulf of Mexico by 96 hrs. This is the second time the CMC suggests development from this system (the first time was mentioned in paragraph P3 of discussion #30 on the morning of July 1). Taking this CMC solution superficially at this time with no other models on board.

P4...Surface ridge dominates much of the open Atlantic basin. A western 1026 mb center midway between North Carolina and Bermuda remains stacked 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 1032 mb center near western Europe is supported by northeastern convergence of the western Europe upper anticyclone 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 central US upper trough...and this upper trough has been 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. The favorable tropical upper ridging was becoming squeezed between paragraph P6 upper vorticity retrograding into Florida from the east and the central US upper trough to the northwest...but upper winds between now and 48 hrs are becoming more favorable again with the paragraph P6 upper vorticity dissipating and the central US upper trough evolving into a weakened TX/MX upper vortex. Despite the continued designation as Invest 94-L and continued mention of this disturbed weather in the NHC Tropical Weather Outlook...their are no signs of organization as the surface troughing is to the northwest of the thunderstorms. This is because the surface troughing like a non-tropical or subtropical system continues to be supported by eastern divergence of the central US upper trough. This places the surface trouhging in less favorable southwesterly shear ahead of the upper trough in addition to land interaction with the Texas and Mexico coasts. Perhaps the latent heat release of the thunderstorms could inflate the tropical upper ridging...with the strengthening outflow of the upper ridging supporting surface pressure falls that might allow new surface troughing to develop over open water. In the event the storms organize around any open water surface trough...I will upgrade this to a special feature. After 48 hrs...the favorable tropical upper ridging will become squaushed out by paragraph P3 upper vortex coming in from the east...finally bringing an end to this disturbance.

P6...Inverted upper trough previously over the east Florida coast and Cuba is now over the Florida peninsula and continues to weaken. Inverted upper trough in the central Caribbean persists 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. Its upper anticyclone west of Portugal has moved into western Europe and out of the above charts...with a new upper ridge axis flaring up over the Azores due to warm air advection ahead of the 1013 mb low mentioned in paragraph P1. This upper ridging continues to extend southwest into the Lesser Antilles and now into the east half of the Caribbean...with low-latitude upper ridging also present over the Cape Verde Islands extending into W Africa. Embedded SW-NE oriented series of upper vorticity features persists from the Canary Islands to the waters W of the Cape Verde Islands. Days ago the south end of this upper ridging (in conjunction with the south end of the paragraph P4 surface ridge) advected dry Saharan air from Africa...large swaths of which still remain as shown by brown shading in the above thermo chart. Since this upper ridging developed a low-latitude structure over the Cape Verde Islands that created upper outflow and resulting moistening lift over the ocean surface...the supply of dry Saharan air has ended as indicated by the current shades of white and blue toward Africa in the lower-right of the above thermo chart (see paragraph P7 of discussion #32 for development of low-latitude upper ridging over the Cape Verde Islands).

P8...Tropical wave previously heading into Central America was dropped from NHC TAFB maps within the last 24 hours...perhaps dissipating in the unfavorable southeastern convergnce of the paragraph P5 tropical upper ridging.

P9...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles has crossed the Lesser Antilles into the northeastern Caribbean. Currently the wave appears suppressed by swaths of dry Saharan air mentioned in paragraph P7.

P10...During discussion #33...Meteosat-9 satellite animation appeared to suggest the most impressive tropical wave of the season thus far was rolling off of Africa. In the last two days...it appears the dominance in this region now goes to the tropical wave Invest 95-L mentioned in the above special feature section while this suspect tropical wave has rapidly lost most of its activity. However I have marked this suspect tropical wave at a location over the Cape Verde Islands for the sake of continuity from my previous discussions...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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3. WunderAlertBot (Admin)
7:02 AM GMT on July 08, 2013
NCHurricane2009 has created a new entry.
2. nigel20
3:25 AM GMT on July 07, 2013
Thanks NC!
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1. Bluestorm5
3:15 AM GMT on July 07, 2013
Very nice, NC09! Always love your posts!
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