2013 Atlantic Hurricane Season Birdseye Discussion #78

By: NCHurricane2009 , 7:15 AM GMT on August 28, 2013

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...WEDNESDAY AUGUST 28 2013 3:15 AM EDT...
Eastern Atlantic tropical wave has become a little better organized within the last day while continuing to have the potential for additional development. See special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_27_2013_2015Z_zps3bca4c48.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-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_27_2013_2015Z_zps21fe9af6.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).

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Tropical wave southwest of the Cape Verde Islands is entering the waters midway between the Cape Verdes and Lesser Antilles while becoming better organized as ittakes advantage of enhanced outflow and low shear beneath eastern Atlantic upper ridge (paragraph P5). The southwest end of axis of upper vorticity embedded in eastern Atlantic upper ridge is breaking off and retrograding westward and away...keeping the tropical wave under the favorable conditions. Therefore I am maintaining this tropical wave as a special feature on this blog while considering it a high risk of eventual tropical cyclone formation. Marine interests in the open tropical Atlantic east of the Lesser Antilles...as well as interests in the Lesser Antilles...should continue to stay tuned over the next few days. Although this tropical wave has yet to be introduced into the National Hurricane Center's traditional 48-hour tropical weather outlook...it has been mentioned in their new 5-day outlook product during the last couple of days.

...MID-LATITUDES DISCUSSION...
P1...Upper ridge persists over the central US. Southern convergence of upper ridge supports 1023 mb surface ridge over the eastern US previously supported by W Atlantic upper trough mentioned in paragraph P2. To the north of the upper ridge...a shortwave upper trough impulse is arriving into the NW Atlantic from the NE US while associated 1007 mb frontal depression is over Atlantic Canada. Another such impulse with 1008 mb frontal depression is currently over north-central Ontario about to cross over southern Hudson Bay. Further north...an upper trough and associated surface frontal cyclone that has persisted over northern Canada is entering the top-center of the above atmo chart while the western convergence of this upper trough supports surface ridge over northern Hudson Bay.

P2...Upper trough over the western Atlantic has broken into a few shortwave upper troughs...including one southeast of Greenland whose eastern divergence is supporting 1000 mb frontal cyclone...another shortwave over eastern Newfoundland and NW Atlantic whose eastern divergence supports 1011 mb frontal cyclone...another shortwave in the vicinity of Bermuda...and cut-off upper vortex over south Florida. The National Hurricane Centerin their 48-hour Tropical Weather Outlook has highlighted the upper vortex as its eastern divergence supports some disturbed weather over the W Bahamas...W Cuba...and south Florida...in addition to a surface trough over the W Bahamas and waters east of Florida. However tropical development appears unlikely due to high surface pressures of paragraph P1 eastern US surface ridge and paragraph P4 open Atlantic surface ridge.

P3...Cut-off upper vortex previously over the Azores has become assimilated into axis of upper vorticity mentioned in paragraph P5 below. NE Atlantic upper ridge persists.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1030 mb center north of the Azores supported by southern convergence of paragraph P3 NE Atlantic upper ridge. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P5...Upper anticyclone persists over central Mexico whose upper outflow supports continued cloudiness and thunderstorms even though the remnant low of Fernand has dissipated. Large eastern Atlantic and Caribbean low-latitude upper ridge persists. This upper ridge remains split by embedded axis of upper vorticity stretching from the waters east of the Lesser Antilles and into the waters south of the Azores. A fragment of this upper vorticity has fractured off while escaping into western Europe and NW Africa.

P6...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently moving across Central America and the western Caribbean while it is producing an impressive area of thunderstorms supported by enhanced poleward outflow at the west end of paragraph P5 Caribbean/eastern Atlantic upper rige. Tropical development is not expected here due to land interaction with Central America.

P7...Tropical wave previously midway between the Cape Verdes and Lesser Antilles is approaching the northern Lesser Antilles and is currently suppressed by dry Saharan air mentioned in paragraph P4.

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