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By: NCHurricane2009 , 12:47 AM GMT on July 24, 2013
...TUESDAY JULY 23 2013 8:47 PM EDT...
High probability of a tropical cyclone this week in the waters between the Cape Verde Islands and Lesser Antilles from vigorous tropical wave that has become better organized in the eastern tropical Atlantic. See special feature section below for additional details. It is quiet elsewhere in the Atlantic tropics.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1330Z-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).
...SPECIAL FEATURE...TROPICAL WAVE INVEST 98-L...
While taking advantage of low shear and enhanced upper outflow associated with its own upper anticyclone mentioned in paragraph P7...the vigorous eastern Atlantic tropical wave has organized into a surface low pressure spin while passing south of the Cape Verde Islands during the last 24 hours. As this has occurred...it appears the north half of the system is struggling to develop thunderstorms due to adjacent Saharan dry air mass mentioned in paragraph P7. The thunderstorms are also lopsided a bit to the west due to easterly shear caused by the fact that the upper anticyclone is just north of rather than directly over the system...but additional thunderstorm latent heat release could cause the upper anticyclone to build directly overhead and later on reduce the easterly shear. Additional uncertainty lies ahead...with the tropical wave soon to track toward a pool of cooler waters at and below 26 deg C located due west of the Cape Verde Islands as seen in the above thermo chart. This pool could mean low enough atmospheric instability during the next 24 hours such that the thunderstorms relax...and if this occurs the Saharan dry air has a chance of killing off tropical cyclogensis altogether. On the other hand...this system is so close to becoming a tropical cyclone I would rather not cancel it as a special feature on this blog. Plus the computer models continue to show the favorable upper anticyclone staying with this system even after passing by the cool water pool and into richly warmer waters...so tropical cyclone formation could still occur later on if it doesn't become one right before the passage thru the cooler water pool.
Marine interests in the Atlantic tropical waters between the Cape Verde Islands and the Lesser Antilles should monitor the progress of this tropical wave over the next few days as it gets steered generally westward by deep-layered easterlies south of the paragraph P6 surface ridge and paragraph P2 north-central Atlantic upper ridge. Even though the paragraph P7 mid-ocean upper vorticity will retrograde westward while getting pushed by this tropical system's upper anticyclone and south side of paragraph P2 north-central Atlantic upper ridge...longer-range computer model runs suggest this tropical wave will eventually catch up to the unfavorable environment of the upper vorticity as it nears the Lesser Antilles. However interests in the Lesser Antilles should still keep a wary eye on this tropical system until further notice.
P1...Upper trough previously over the central US and central Canada is pushing across the Great Lakes and eastern Canada. Its eastern divergence formerly supported 996 mb surface frontal cyclone currently just south of Hudson Bay that has now become stacked with the non-divergent upper trough axis. Eastern divergence of the upper trough now supports new 1003 mb depression currently over the NE US that will gradually assume dominance while the 996 mb center begins decay. Western convergence of this upper trough supports 1019 mb ridge building over the north-central US and south-central Canada.
P2...Upper trough previously over eastern Canada has merged with NE Atlantic upper trough mentioned in paragraph P3. Surface 990 mb frontal cyclone over eastern Canada has become absorbed by north side of 996 mb cyclone mentioned in paragraph P1. Low-level warmer air ahead and south of the absorbing 996 mb surface frontal cyclone's cold fronts supports upper ridging over the SW US...northern Gulf of Mexico...the waters offshore of the eastern US...and into the north-central Atlantic.
P3...Large NE Atlantic upper trough remains stationary as its eastward progression is blocked by deep-layered ridge over Europe. At the surface...the surface 1005 mb center previously moving toward the British Isles of Europe has become replaced by new 1004 mb center also moving NE toward the British Isles. This 1004 mb center has developed along the occluded front of the absorbed paragraph P2 990 mb cyclone while supported by eastern divergence of the upper trough. Western convergence of the upper trough meanwhile supports 1021 mb ridge east of Newfoundland.
P4...What is left of east-west surface troughing in the open Atlantic...formerly supported by divergence between easterlies south of the paragraph P2 north-central Atlnatic upper ridge and mainstream mid-latitude westerlies...is now a dissipating 1019 mb surface low west of the Canary Islands and south of the Azores.
P5...Upper vortex persists over the Bay of Campeche.
P6...Surface ridge dominates much of the open Atlantic basin...with a current westward extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 SW US upper ridge. The remainder of the surface ridge is supported by southeastern convergence of paragraph P2 north-central Atlantic upper ridge (as well as paragraph P2 upper ridging offshore of eastern US) and western convergence of paragraph P7 upper vortex south of Bermuda.
...TROPICAL BELT DISCUSSION...
P7...Low-latitude upper ridge covering the eastern tropical Atlantic remains split into one upper anitcyclone centered over the northern Lesser Antilles and another upper anticyclone associated with the t-storm latent heat release of tropical wave Invest 98-L...with large-scale mid-ocean upper vorticity between the two upper anticyclones. Southern Caribbean t-storms mentioned in paragraph P8 of the previous discussion have moved into Nicaragua and Honduras...with the associated latent heat release continuing to support upper ridge over Central America (central Caribbean upper trough persists between the Central America upper ridge and northern Lesser Antilles upper anticyclone). Low-level warm air advection ahead of paragraph P1 996 mb cyclone has intensified paragraph P2 upper ridging offshore of the eastern US such that the upper vortex previously SW of Bermuda has been pushed eastward to the waters south of Bermuda. South end of aforementioned northern Lesser Antilles upper anticyclone...in conjunction with the south end of the paragraph P6 surface ridge and south end of paragraph P2 north-central Atlantic upper ridge...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. Open central Atlantic upper vortex continues retrograding westward around the paragraph P2 north-central Atlantic upper ridge...and while over sea-surface temps in the 27 to 28 deg C range it appears the vertical contrast between the warm waters and cold air of the upper vortex continues to support instability and t-storms east of Bermuda.
P8...Tropical wave previously over Puerto Rico is now over Hispaniola (Haiti and the Dominican Republic). Its thunderstorm activity has declined while moving below oppressive and non-divergent upper atmosphere due south of the paragraph P7 upper vortex south of Bermuda.
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
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