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By: NCHurricane2009 , 8:03 PM GMT on August 24, 2013
...SATURDAY AUGUST 24 2013 4:00 PM EDT...
Dry Saharan air in the Atlantic tropics appears to have diminished in areal extent. In addition...a disturbance moving across the Yucatan peninsula has the potential for development while continuing west-northwest into the Bay of Campeche waters as outlined in paragraph P7 below. Therefore I have resumed daily discussions on the Atlantic tropics.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0726Z-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...
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...Upper ridge has built across the central US. To the north of the upper ridge...the next shortwave upper trough and surface frontal system in the mid-latitudes is entering the upper-left of the above charts from Canada's Hudson Bay.
P2...Upper trough moving across Hudson Bay during previous discussion #74 is currently across the eastern US...eastern Canada...the high seas between Greenland and Canada...and Greenland. Associated surface low supported by eastern divergence of upper trough is currently over Iceland while the lenghty cold front extending from the surface low is entering the western Atlantic...and reaches into the southeastern US and central US. Western convergence of the upper trough supports 1026 mb surface ridge over SE Canada and the NE US.
P3...Shortwave upper trough and vigorous frontal cyclone over the north-central Atlantic mentioned in previous discussion #74 has since ejected northeastward out of the scope of the above charts...but leaves behind a shortwave upper trough and associated surface trough currently located in the NW Atlantic. Upper vortex over Illinois mentioned in previous discussion #74 has since moved eastward into the Atlantic waters in the vicinity of Bermuda as a shortwave upper trough. Relatively warmer air ahead of these upper vorticity features supports NE Atlantic upper ridge.
P4...Surface ridge dominating much of the open Atlantic is anchored by 1031 mb center just north of the Azores supported by southeastern convergence of paragraph P3 NE Atlnatic upper ridge. Recently the surface 1031 mb center has become vertically stacked with the upper ridge center. 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 vorticity previously in the western Caribbean has been pushed into the western Gulf of Mexico due to latent heat release associated with tropical disturbance Invest 95-L mentioned in paragraph P7. The Caribbean upper anticyclone mentioned in paragraph P6 of discussion #74 has become associated with the outflow of disturbance Invest 95-L and is currently centered over the SE Gulf of Mexico. Relatively lower pressures east of the upper anticyclone supported the formation of upper vortex over the Lesser Antilles as mentioned in paragraph P8 of discussion #74...and currently this upper vortex is centered over southern Hispaniola. To the east of the upper vortex...large eastern Atlatnic low-latitude upper ridge persists. This eastern Atlantic upper ridge is currently split by embedded axis of upper vorticity stretching from the waters NW of the Cape Verde Islands and into the Canary Islands and Morocco. This upper vorticity is a combination of Canary Islands cut-off upper trough mentioned in paragraph P3 of discussion #74 and a cut-off fragment of upper trough moving into western Europe mentioned in paragraph P2 of discussion #74.
P6...Long front extending from north-central Atlantic surface cyclone mentioned in paragraph P2 of discussion #74 left behind surface trough in the northeastern Gulf of Mexico. This system acquired the characteristics of a tropical disturbance while exhibiting thunderstorms supported by outflow of northern Gulf upper anticyclone mentioned in paragraph P2 of discussion #74...and has been mentioned in the National Hurricane Center Tropical Weather Outlook over the last couple of days. The surface trough appears to have dissipated offshore of Louisiana as of this morning in a more hositle environment of westerly vertical shear on the north side of the outflow of disturbance Invest 95-L and south side of paragraph P2 upper trough.
P7...Tropical wave has moved across the western half of the Caribbean over the last couple of days is now entering the southeastern Mexico and the Bay of Campeche while supppressed by western Gulf upper vortex mentioned in paragraph P5. While it was predicted during special update #74A that this tropical wave would not develop due to the upper vorticity....the tropical wave has triggred an extensive area of western Caribbean thunderstorms moving into the Yucatan peninsula that appear to be organizing into a surface low pressure spin located behind the tropical wave and centered over the Mexico/Belize/Guatemala border. This system has recently been upgraded to disturbance Invest 95-L on the Naval Research Laboratory site of the US Navy. If the latent heat release of the thunderstorms continue to show signs of wedging out the western Gulf upper vorticity while the spin moves over warm Bay of Campeche waters during the next 24 hours...I will be upgrading it to a special feature on this blog. Regardless of further development...expect this system to generally track west-northwest across the Bay of Campeche and into eastern Mexico over the next couple of days while steered about the southwestern quadrant of paragraph P2 1026 mb ridge.
P8...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently approaching the Lesser Antilles while inactive in enviornment of dry Saharan air mentioned in paragraph P4. Satellite animation over the last few days suggested the east side of this tropical wave left behind a small low pressure spin west of the Cape Verde Islands that is now marked as a 1011 mb low midway between the Cape Verdes and Lesser Antilles also inactive in enviornment of dry Saharan air.
P9...Tropical wave with thunderstorms and low pressure spin has recently emerged from Africa and is currently positioned southwest of the Cape Verde Islands. Although this system is taking advantage of low shear and enhanced outflow beneath paragraph P5 eastern Atlnatic upper ridge...it is headed toward unfavorable upper winds associated with axis of upper vorticity to the northwest also mentioned in paragraph P5.
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