2013 Atlantic Hurricane Season Birdseye Discussion #60

By: NCHurricane2009 , 4:31 PM GMT on August 04, 2013

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...SUNDAY AUGUST 4 2013 12:31 PM EDT...
Tropical Depression Dorian degenerates into remnant low offshore of the southeastern United Staes as of yesterday afternoon and will be merging with a frontal boundary as it transitions into a non-tropical remnant gale. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_4_2013_1315Z_zps5217f71f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1327Z-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 Aug_4_2013_1315Z_zpsa092708b.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 persists over eastern Canada and the northeastern US. Eastern divergence of the upper trough formerly supported frontal cyclone centered over NE Hudson Bay which has since lifted northward out of the above charts while weakening below the upper trough axis. Eastern divergence of the upper trough now supports 1002 mb frontal depression that has moved from the Great Lakes to SE Canada in the last 36 hrs as well as a 1005 mb frontal depression that has tracked from offshore of the NE US and into the waters NE of Newfoundland in the last 36 hrs. Low-level warm air southwest of the upper trough supports southern US upper ridge...and low-level warm air advection ahead of the 1002 and 1005 mb frontal depressions supports western Atlantic upper ridge which has recently split into an eastern extension of southern US upper ridge and another upper ridge over Greenland. Convergence behind the upper trough supports 1025 mb surface ridge building into the central US from central Canada.

P2...Deep-layered vortex south of Greenland and NE Atlatnic upper trough have merged into amplified upper trough and surface frontal system offshore of western Europe.

P3...Surface ridge dominates much of the open Atlantic basin...with a current westward 1019 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P1 southern US upper ridge. The dominant open Atlantic centers anchoring this ridge...currently at 1022 and 1030 mb...are supported by western convergence of paragraph P2 NE Atlantic upper trough and SE convergence of paragraph P1 western Atlantic upper ridge. In conjunction with south side of paragraph P6 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.

...TROPICAL BELT DISCUSSION...
P4...Broad upper vortex previously NE of the Lesser Antilles is beginning to retrograde southwestward into the the NE Caribbean Sea while moving around paragraph P1 western Atlantic upper ridge. A new upper vortex ENE of Bermuda has developed in relatively lower pressures between paragraph P1 western Atlantic upper ridge and paragraph P6 eastern Atlantic upper ridge.

P5...Tropical wave previously moving into the Bay of Campeche and SE Mexico has exited the scope of this blog while moving into the eastern Pacific. What is left of inverted upper trough over the western Caribbean is a small upper vortex moving into the Yucatan while retrograding around paragraph P1 southern US upper ridge. Tropical Depression Dorian offshore of the SE US has collapsed into a remnant low as of yesterday afternoon due to northerly vertical wind shear on east flank of southern US upper ridge...but has recently deepened to 1010 mb and developed a southward extending surface trough with thunderstorms due to split flow upper divergence between the northerlies on the east flank of southern US upper ridge and westerlies ahead of paragraph P1 upper trough. In the next 24 hrs...expect the remnant of Dorian to accelerate NE across the open NW Atlantic while transitioning into a non-tropical frontal low supported by eastern divergence of paragraph P1 upper trough (and as such I will move it to the mid-latitudes section during my next discussion).

P6..The paragraph P4 broad upper vortex continues to split low-latitude upper ridging into one upper anticyclone (upper ridge) over the southern Caribbean whose outflow continues supporting an increase in thunderstorms in the area...and a second upper upper ridge in the eastern Atlantic featuring an embedded inverted upper trough due west of the Cape Verde Islands.

P7...Tropial wave previously west of the Cape Verde Islands is now midway between the Lesser Antilles and Cape Verde Islands. With the exception of thunderstorms along the ITCZ at its south end...this tropical wave remains inactive while embedded in dry Saharan air mentioned in paragraph P3 and supressive (non-divergent) environment of inverted upper trough mentioned in paragraph P6.

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2. WunderAlertBot (Admin)
2:14 AM GMT on August 06, 2013
NCHurricane2009 has created a new entry.
1. nigel20
6:02 PM GMT on August 04, 2013
Thanks again NCH! I really appreciate the work that you put into these blog posts.
Member Since: November 6, 2010 Posts: 12 Comments: 8488

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