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By: NCHurricane2009 , 5:46 AM GMT on August 15, 2014
...FRIDAY AUGUST 15 2014 1:45 AM EDT...
The vigorous tropical wave previously south of the Cape Verde Islands is currently southwest of the islands. Meanwhile a central Atlantic upper trough...as marked by a blue dashed line in the atmospheric features chart below...is shifting south in advance of a building central Atlantic upper ridge as marked by a blue H. The southward digging of the central Atlantic upper trough is creating a split in the low-latitude tropical upper ridging that has resulted in the formation of an inverted upper trough in the split and to the west of the tropical wave. Even though the tropical wave has recently formed a low pressure spin...it has also recently lost thunderstorm activity while sliding beneath the inverted upper trough (which has temporarily closed off into an upper vortex as marked by a blue L over the south part of the tropical wave). Expect the southward digging central Atlantic upper trough and inverted upper trough to merge in the next 24 hours overhead of the tropical wave...which will continue to suppress development of this system. As the combined upper trough later shifts westward around the south side of the central Atlantic upper ridge...this may allow this system to be in a marginally favorable light southerly shear environment on the east side of the upper trough...or even in a more favorable environment below a tropical upper ridge to expand from the eastern Atlantic in the wake of the upper trough. However this system is still not likely to develop while ingesting the dry Saharan air layer presently to the north and west.
The vigorous tropical wave previously over western Africa is emerging over the eastern tropical Atlantic waters while well-organized. I have upgraded it to a special feature on this blog with the expectation that it will become the next tropical cyclone in the Atlantic basin. Interests in the Cape Verde Islands should monitor the progress of this system as it is expected to pass just south of the islands. See special feature section below for additional details on this system.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1915Z-released WPC analysis.
Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.
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).
...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM WESTERN AFRICA...
Current prognosis...As of 0000Z infrared satellite imagery suggested that the tropical wave emerging from western Africa features spiral bands of showers and thunderstorms organizing around a low pressure spin centered near 12.5N-17.5W.
Atmospheric Outlook for the Forecast Period...A northwestern Atlantic low pressure has deepend from 1013 to 1008 mb in the last 24 hours while becoming re-enforced by the vigorous 1002 mb frontal cyclone and associated upper trough over eastern North America...which will cause this low to weaken the Atlantic low-level subtropical ridge as it shifts into the eastern Atlantic during the next 96 hours. Therefore my forecast below slows the westward track and deflects it a bit northward as the ridge weakens. By 120 hours the low-level ridge is forecast to rebuild which is why my final forecast point suggests a track bending more westward with an increase in forward speed. In the upper layers...a central Atlantic upper ridge is pushing a central Atlantic upper trough southward...which is later expected to retrograde westward around the south side of the upper ridge. However because this system is expected to take a slow westward track...it is expected to stay in a favorable low shear/good outflow environment associated with a tropical upper ridge to expand in the eastern tropical Atlantic in the wake of the retrograding upper trough.
Thermodynamic Outlook for the Forecast Period...The forecast track below will take the circulation center of this system along a 27 deg C sea-surface temperature isotherm. This will allow the northern part of the circulation to interact with less favorable water temps at or below 26 deg C until 120 hours when this system will be tracking into warmer waters. The potential interaction with milder waters to the north for the first 96 hours and dry Saharan air also to the north makes me show a gradual as opposed to rapid strengthening in my forecast below.
24 Hr Forecast (0000Z August 16)...Organized tropical low centered just southeast of the Cape Verde Islands near 12.5N-20.5W.
48 Hr Forecast (0000Z August 17)....40 mph max sustained wind tropical storm centered just south of the Cape Verde Islands near 12.5N-24W.
72 Hr Forecast (0000Z August 18)...45 mph max sustained wind tropical storm centered just southwest of the Cape Verde Islands near 13N-26.5W
96 Hr Forecast (0000Z August 19)...50 mph max sustained wind tropical depression centered near 14N-29W
120 Hr Forecast (0000Z August 20)...60 mph max sustained wind tropical storm centered near 14N-33W
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