2012 Atlantic Hurricane Season Birdseye Discussion #77

By: NCHurricane2009 , 10:47 PM GMT on August 12, 2012

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...AUGUST 12 2012...6:48 PM EDT...
Conditions for tropical depression seven to regenerate are increasing. Interests in the western Caribbean Sea should monitor the progress of the remnants. See special feature section below for further details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released HPC 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...REMNANTS OF SEVEN...
Remnant tropical wave of depression seven crossed the Lesser Antilles last night...and is currently moving westward across the eastern Caribbean Sea. The remnants have overcome the first unfavorable factor for tropical cyclone regeneration...which is unfavorable southwesterly shear from paragraph P3 upper vorticity retrograding into the Caribbean Sea. This is either due to faster-than-expected breakup of the upper vorticity on its own accord...or latent heat release from the t-storms expanding the paragraph P5 E Atlc upper ridge into the east Caribbean to facilitate the breakup...or a combination of both theories. There are no more unfavorable southwesterly shearing upper winds in the upstream environment...instead less hostile easterly upper winds across the central Caribbean inverted upper trough (paragraph P3) and west Caribbean upper ridge (paragraph P5). Coupled with the westward expansion of E Atlc upper ridge (paragraph P5) which is ventilating the system quiet well at this hour...the remnants have a better opportunity for tropical cyclone regeneration than I thought in the previous discussion.

However...there is no imminent threat of tropical cyclone regeneration at this hour...with some lingering unfavorable factors that still lie upstream of the remnants of Seven. The east side of the paragraph P5 W Caribbean upper ridge promotes upper convergence (like a typical mid-latitude upper ridge wave)...which is strengthening the dry air to Seven's west (source of dry air mentioned in paragraph P4). It is still possible that the remnants either ingest this dry air as it tries to spin up...or that the brisk west motion of the remnant tropical wave causes it to outrun the favorable E Atlc upper ridge and move into the dry air and less favorable central Caribbean inverted upper trough (paragraph P3).

...MID-LATITUDES DISCUSSION...
P1...Upper trough regime over central US and central Canada has spread into eastern areas and all of the Atlantic high seas. Frontal cyclone SE of Greenland in previous discussion is heading into western Europe (upper-right corner of above atmo chart)...while another frontal cyclone (1002 mb as of 1930Z HPC) dives into the top-center of above atmo-chart from Greenland. Both frontal cyclones' cool air advection support a longwave upper trough covering the entire Atlantic high seas...whose western upper convergence supports a 1023 mb ridge on the SE Canada coast. Deep-layered cyclone over E Great Lakes in previous discussion is moving NE into eastern Canada...and upper convergence behind this system supports a 1018 mb ridge over the SE US and 1017 mb ridge over Minnesota. Yet another shortwave upper trough has developed over the central US in this regime...supported by cool air advection from frontal system diving in from W Canada. Low-level warm air advection ahead of eastern Canada deep-layered cyclone supports W Atlantic upper ridge...while SW US upper ridge persists behind this regime.

P2...NE Atlantic upper trough in previous discussion has exited the picture while moving into Europe.

P3...Mid-ocean upper vorticity persists....still featuring a few upper vortex centers. One upper vortex is moving from Gulf of Mexico into NE Mexico while retrograding around paragraph P1 SW US upper ridge. A second and quiet elongated upper vortex is digging southwestward around the W Atlantic upper ridge (paragraph P1)...a fragment of which has split off and retrograded into the central Caribbean as an inverted upper trough. A third upper vortex still shows faintly in the above atmo chart 200 mb wind barbs...located SSW of the Azores.

P4...Atlantic surface ridge with 1018 mb to 10XX mb centers is supported by a few upper convergent sources while stretching from Gulf of Mexico to waters offshore of W Europe....including convergence SE of the of west Atlantic and SW US upper ridges (paragraphs P1)...and convergence behind Atlantic high seas upper trough (paragraph P1). In conjunction with south side of W Atlantic upper ridge (paragraph P1)...south side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.

...TROPICAL BELT DISCUSSION...
P5...Upper ridging across Atlantic tropics remains concentrated into two areas. An upper ridge is in the western Caribbean as a southward extension of W Atlantic upper ridge in paragraph P1...and is supported by relatively higher pressures between the Gulf of Mexico upper vortex and central Caribbean inverted upper trough mentioned in paragraph P3. Tropical upper ridging remains firmly established in eastern tropical Atlantic.

P6...Tropical wave over SE Mexico/Bay of Campeche in previous discussion has moved into the eastern Pacific in last 24 hrs...and therefore will no longer be mentioned on this blog.

P7...Remnants of Florence have dissipated north of the Bahamas in last 24 hrs.

P8...Remnants of tropical depression seven crossed the Lesser Antilles last evening...and are currently in the eastern Caribbean. Due to increased risk of regenerating into a tropical cyclone that was not previously seen on this blog...this system has been moved into its own special feature section. See above special feature section for further details on this system.

P9...Tropical wave Invest 93-L continues pushing west...and its large low pressure spin is now far WNW of the Cape Verde Islands and far ENE of the Lesser Antilles. Even though it is still under favorable upper outflow beneath paragraph P5 E Atlc upper ridge...and its westward track is still taking it into increasingly warmer waters...I still am not re-considering this a special feature on this blog due to weak t-storm activity caused by ingestion of dry air (source of dry air mentioned in paragraph P4).

P10...A tropical wave with currently disorganized t-storm activity is emerging from the west coast of Africa into the Atlantic tropical belt (lower-right corner of above atmo chart).

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1. nigel20
11:32 PM GMT on August 12, 2012
Thanks for the blog update, NC!
Member Since: November 6, 2010 Posts: 12 Comments: 8489

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