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2013 Atlantic Hurricane Season Birdseye Discussion #44

By: NCHurricane2009 , 4:56 AM GMT on July 17, 2013

...WEDNESDAY JULY 17 2013 1:00 AM EDT...
Atlantic tropics remain quiet...

 photo Jul_16_2013_2045Z_zps4afbe022.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1921Z-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_16_2013_2045Z_zps3eaaaae6.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...Next upper trough and associated surface frontal cyclone is entering the upper-left corner of the above charts from western Canada and Hudson Bay.

P2...Upper trough previously emerging onto the east Canada coast has entered the Atlantic high seas between Canada and Greenland...with eastern divergence of the upper trough supporting an intensifying 988 mb surface frontal cyclone currently south of Greenland. Western convergence of this upper trough supports 1026 mb surface ridge currently over eastern Canada.

P3...Pair of cut-off upper vortices persists in northern Texas and western Gulf of Mexico. Decaying Texas front is now a surface trough supported by eastern divergence of the north Texas upper vortex. Decyaing north-central Atlantic front with 1014 mb depression...NW Atlantic surface low south of Nova Scotia...and now a new surface trough just offshore of the US mid-Atlantic states...all mentioned in paragraph P2 of the previous discussion...persists while now supported by split flow upper divergence between easterlies southeast of the eastern US upper ridge mentioned further down this paragraph and mainstream mid-latitude westerlies. What is now the 1027 mb NE US surface ridge supported eastern US upper ridge with low-level warm air advection on its west side...and in turn SE convergence of the upper ridge supported the surface ridge. Now that the surface and upper ridge centers have become vertically stacked...we have a deep-layered ridge centered over southern Michigan this early morning.

P4...Cut-off upper trough west of the Azores...mentioned in paragraph P3 of the previous discussion...persists. Surface frontal depression west of the Azores also mentioned in paragraph P3 of the previous discussion has weakened into a surface trough while remaining vertically stacked with the upper trough. In the last nine days...a fragment of this upper vorticity had also split southeastward and is currently the upper trough due north of the Canary Islands heading into western Europe (moreover a southwest portion of this upper vorticity had also evolved into what is now the upper vortex due southwest of Bermuda that is retrograding westward about the eastern US upper ridge mentioned in paragraph P3).

P5...Surface ridge dominates much of the open Atlantic basin. The west end of this surface ridge is getting a westward extension tonight while the southern Michigan 1027 mb center in paragraph P3 merges with it. Remainder of the open Atlantic portion of this surface ridge continues to have a 1026 mb center west of Europe.

P6...Low-latitude upper ridge axis previously over the Cape Verde Islands extending into W Africa continues lifting northward and has expanded westward toward the Lesser Antilles/E Caribbean in the wake of the weakening and or retrograding upper vorticity features mentioned in paragraph P4. Upper trough vorticity has recently diminished in the central Caribbean such that the low-latitude upper ridge axis is beginning to join the Caribbean portion of low-latitude upper ridging which has recently developed a south-central Caribbean upper anticyclone and associated t-storms near and over Panama. Northern Yucatan and central Gulf of Mexico t-storms mentioned in paragraph P5 of the previous discussion have recently left the domain of the Caribbean low-latitude upper ridging...transfering into the western Gulf of Mexico while becoming associated with a new surface trough supported by split flow upper divergence at the boundary between the two upper vortices mentioned in paragraph P3. South end of the aforementioned low-latitude upper ridge axis...in conjunction with the south end of the paragraph P5 surface ridge...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Surface trough previously just east of Florida (and associated upheaveal in t-storms that has occurred with it in the last 24 hrs) is now entering the eastern Gulf of Mexico while currently supported by split flow upper divergence at the boundary between the west side of the paragraph P4 upper vortex SW of Bermuda and paragraph P3 upper vortex in the western Gulf of Mexico. Eastern divergence of the paragraph P4 upper vortex SW of Bermuda continues supporting relatively new surface trough and associated t-storms north of Puerto Rico.

P8...Tropical wave previously approaching the Lesser Antilles has crossed the islands into the eastern Caribbean...and remains suppressed by dry Saharan air mentioned in paragraph P6. Albeit it has recently begun entering an area of moistening eastern Caribbean air associated with enhanced poleward upper outflow at the west end of the expanding low-latitude upper ridge axis mentioned at the beginning of paragraph P6.

P9...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles is nearing the Lesser Antilles while suppressed by dry Saharan air mentioned in paragraph P6.

P10...Tropical wave with loose t-storm clustering is emerging from western Africa into the Atlantic tropical waters SE of the Cape Verde Islands tonight. No computer model support for this tropical wave's development even though it will traverse below the low shear and enhanced upper outflow enviroment of low-latitude upper ridge axis mentioned in paragraph P6. This is probably because the tropical wave will likely choke on dry Saharan air like its predecessor tropical waves mentioned in paragraphs P8 and P9.

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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