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2013 Atlantic Hurricane Season Birdseye Discussion #47

By: NCHurricane2009 , 6:14 PM GMT on July 20, 2013

...SATURDAY JULY 20 2013 2:15 PM EDT...
Tropical wave has moved from Haiti and into the western Caribbean and Bahamas region since the previous discussion. Their are no signs of development as it moved into favorable upper winds...see paragraph P10 for details.

Thunderstorm activity over the central Gulf of Mexico continues to be associated with surface troughing mentioned in paragraph P8 interacting with upper divergence around a Louisiana upper vortex mentioned in paragraph P5. This area was introduced into the National Hurricane Center Tropical Weather Outlook yesterday afternoon and is now being canncelled from the outlook due to lack of persistence in the thunderstorms.

I have inspected the Naval Research Laboratory site of the US Navy and found that their is no Invest number assigned to the above-mentioned Gulf activity. However in their archives I found that the short-lived western Gulf of Mexico activity that occured on July 17 early morning (paragraph P6 of discussion #44) was breifly classified as Invest 97-L even though that activity was never introduced into the National Hurricane Center Tropical Weather Outlook. This info was not conveyed on this blog earlier...so I thought I would mention it now.

 photo Jul_20_2013_1215Z_zps7e133cc8.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-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_20_2013_1215Z_zps9a73d8aa.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 previously over central Canada has become more amplified while moving into eastern Canada thanks to cool air advection on back side of surface frontal depression that has also moved from central to eastern Canada in last 36 hrs while intensifying from 998 to 990 mb (the intensification of surface frontal depression was in turn due to eastern divergence of amplifying upper trough). Western convergence of the amplified upper trough supports building surface ridge over central Canada. Low-level warmer air ahead of the surface frontal depression's cold fronts supports upper ridge over the SW US...another upper ridge over the SE US...and upper ridge that has moved from the eastern US (mentioned in paragraph P4 of the previous discussion) and into the NW Atlnatic.

P2...Upper trough and associated surface frontal cyclone previously between Canada and Greenland has evolved into deep-layered vortex of less-than-1004 mb due south of Greenland. Western upper-level convergence of the deep-layered vortex supports 1020 mb surface ridge east of Newfoundland.

P3...Upper trough persists SE of Greenland...extending now into the Canary Islands. 1005 mb frontal depression north of the Azores...mentioned in paragraph P4 of the previous discussion...has moved NNW to the waters just SE of Greenland while rounding the west side of deep-layered ridging consisting of Europe upper ridge and Europe fracture of paragraph P6 surface ridge. This surface frontal depression is currently just below 1008 mb and is also deep-layered while aligning with upper vorticity of the upper trough. Eastern divergence of the upper trough supports new 1012 mb frontal depression NW of Spain that has also recently become deep-layered while aligning with the upper vorticity of the upper trough. Finally...western convergence of this upper trough supports 1019 mb surface ridge currently just NE of the Azores.

P4...Lengthy east-west surface troughing in the open central Atlantic...mentioned in paragraph P4 of the previous discussion...currently persists while generally supported by split flow upper divergence between easterlies southeast of the NW Atlantic upper ridge mentioned in paragraph P1 and mainstream mid-latitude westerlies. This surface troughing wraps all the way into 1012 mb frontal depression NW of Spain mentioned in paragraph P3.

P5...North-central Gulf of Mexico upper vortex has moved NW into Lousiana while moving about SE US upper ridge mentioned in paragraph P1.

P6...Surface ridge dominates much of the open Atlantic basin...with a current westward extension onto the US Gulf coast. The open Atlantic portion of this surface ridge is supported by southeastern convergence of paragraph P1 NW Atlantic upper ridge. The Europe portion of this surface ridge has fractured from the main open Atlnatic portion thanks to the digging in of paragraph P3 and P2 upper vorticity and surface frontal depression features.

P7...Prominent low-latitude upper ridge axis continues covering the eastern tropical Atlantic and eastern Caribbean. Upper vortex previously in the eastern Caribbean has retrograded further west into the central Caribbean as an inverted upper trough while steered around paragraph P1 NW Atlantic upper ridge...and upper vortex previously south of Bermuda is now SW of Bermuda while also steered around paragraph P1 NW Atlantic upper ridge...with both of these upper vortices continuing to seperate the aforementioned low-latitude upper ridge axis from the Caribbean portion of low-latitude upper ridging. The Caribbean portion of low-latitude upper ridging has recently consolidated as a western Cuba upper anticyclone in the widening gap between the paragraph P5 upper vortex and upper vortex SW of Bermuda mentioned earlier in this paragraph. South end of all the low-latitude upper ridging in this paragraph...in conjunction with the south end of the paragraph P6 surface ridge...is also advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Lastly...the north-central Atlantic upper anticyclone mentioned in paragraph P7 of the previous discusison has become absorbed by paragraph P1 NW Atlnatic upper anticyclone...but the new upper vortex in the open central Atlantic due south of the absorbed upper anticyclone is beginning to retrograde south and west about the paragraph P1 NW Atlantic upper anticyclone.

P8...Central Gulf of Mexico surface trough mentioned in paragraph P8 of the previous discussion has recently dissipated...but thunderstorms that have been pulsing up and down in intensity continue to be supported by eastern divergence of paragraph P5 upper vortex currently centered over Louisiana. These thunderstorms were impressive enough yesterday afternoon for the National Hurricane Center to mentioned this area in their tropical weather outlook...but now this area has been removed from their outlook as of this afternoon.

P9...Tropical wave previously moving into Central America is now over SE Mexico and the Bay of Campeche. It is largely inactive while suppressed by westerly shear and lack of upper divergence due south of the Louisiana upper vortex mentioned in paragraph P5.

P10...Tropical wave previously over Haiti developed a northern fracture moving into the Bahamas 36 hrs ago that has just been cancelled as of the 1200Z NHC TAFB surface mapping. Remainder of this tropical wave is currently moving toward Central America and the western Caribbean. Previous prognosis was to watch this tropical wave as it slides below favorable low shear and enhanced upper outflow environment of what is now the western Cuba upper anticyclone mentioned in paragraph P7. Atlhough their are some pop-up thunderstorm clusters supported by this upper outflow environment...they are not impressive enough to suggest tropical cyclone development from this tropical wave...and computer models continue to show no development here.

P11...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles is moving toward the Lesser Antilles. It is entirely suppressed by dry Saharan air mentioned in paragraph P7.

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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