2013 Atlantic Hurricane Season Birdseye Discussion #45

By: NCHurricane2009 , 8:06 AM GMT on July 18, 2013

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...THURSDAY JULY 18 2013 4:07 AM EDT...
Atlantic tropics continue to remain quiet...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_17_2013_2345Z_zpsd9faa4be.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0130Z-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.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_17_2013_2345Z_zps5186b6bc.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).

...MID-LATITUDES DISCUSSION...
P1...Upper trough and associated surface frontal cyclone continues east across Hudson Bay into eastern Canada. Western convergence of the upper trough supports 1023 mb surface ridge over southern Manitoba.

P2...Upper trough previously over the Atlantic high seas between Canada and Greenland is now SSE of Greenland...with eastern divergence of the upper trough supporting a 994 mb surface frontal cyclone currently SSE of the south tip of Greenland. Western convergence of this upper trough supports 1022 mb surface ridge currently just south of Newfoundland. Warm air advection ahead of 994 mb frontal cyclone supports building upper ridge west of Europe

P3...Cut-off upper vortex previously over Texas has shifted westward into southern New Mexico while retrograding about eastern US upper ridge mentioned further down in this paragraph. Decaying north-central Atlantic front...NW Atlantic surface low south of Nova Scotia...and surface trough just offshore of the US mid-Atlantic states...all mentioned in paragraph P3 of the previous discussion...currently persists as surface troughing from the mid-Atlantic states eastward into the open central Atlantic for several hundred miles all still 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 1021 mb surface ridge centered just offshore of the NE US supports eastern US upper ridge with low-level warm air advection on its west side...and in turn SE convergence of the upper ridge supports the surface ridge.

P4...Cut-off upper trough previously west of the Azores is currently the upper vortex just north of the Azores while the associated surface frontal depression has dissipated below it. A southwest portion of this upper vorticity several days ago has evolved into what is now the upper vortex moving into the eastern Gulf of Mexico that continues retrograding westward about the eastern US upper ridge mentioned in paragraph P3.

P5...Surface ridge dominates much of the open Atlantic basin. This surface ridge continues to have a center west of Europe...currently 1030 mb and currently supported by eastern convergence of upper ridge mentioned at the end of paragraph P2.

...TROPICAL BELT DISCUSSION...
P6...Low-latitude upper ridge axis previously over the Cape Verde Islands extending into W Africa has recently lifted northward and has expanded westward into the eastern Caribbean in the wake of the weakening and or retrograding upper vorticity features mentioned in paragraph P4. Upper outflow of Caribbean portion of low-latitude upper ridging supports t-storms that have shifted from Panama and into much of Central America. New upper vortices...one south of Bermuda...one in the Central Caribbean...and one east of the Lesser Antilles...have developed in relatively lower pressures between the low-latitude upper ridging mentioned in this paragraph and eastern US upper ridge mentioned in paragraph P3. South end of the aforementioned low-latitude upper ridging...in conjunction with the south end of the paragraph P5 surface ridge...is also advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Surface trough entering the eastern Gulf of Mexico has undergone a northward expansion into the SE US where a large batch of t-storms developed this past afternoon...this expansion supported by split flow upper divergence between easterlies on the north side of the paragraph P4 eastern Gulf upper vortex and southerlies on the west side of the paragraph P3 eastern US upper ridge. Eastern divergence of the paragraph P4 eastern Gulf upper vortex supports surface trough that has moved from north of Puerto Rico to northeast of the Bahamas in the last 24 hrs...while a divergent upper westerly jet south of the upper vortex and north of the paragraph P6 Caribbean low-latitude upper ridging supports a new surface trough over the western Yucatan. Thunderstorms span the area between the new Yucatan surface trough and surface trough northeast of the Bahamas.

P8...Tropical wave previously in the eastern Caribbean is now in the central Caribbean...and remains inactive while caught in a batch of Saharan dry air accumulated below new upper vortex in the central Caribbean mentioned in paragraph P6.

P9...Tropical wave previously nearing the Lesser Antilles is crossing the islands into the eastern Caribbean this early morning...and although previously suppressed by paragraph P6 Saharan dry now has some cloud and shower actvity supported by split flow upper divergence at the boundary between the paragraph P6 upper vortex east of the Lesser Antilles and paragraph P6 upper vortex south of Bermuda.

P10...Tropical wave previously SE of the Cape Verde Islands is now just west of the islands...with t-storms persisting in its south half while its north half is choking on dry Saharan air mentioned in paragraph P6.

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