2012 Atlantic Hurricane Season Birdseye Discussion #78

By: NCHurricane2009 , 3:48 AM GMT on August 14, 2012

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...AUGUST 13 2012...11:49 PM EDT...
Remnants of tropical depression seven...currently in the central Caribbean Sea...still shows no signs of regeneration. See paragraph P6 for details.

Elsewhere...in the past 24 hrs...there has been an increase in concentrated t-storms southwest of Bermuda (end of paragraph P1) and the southwestern Gulf of Mexico (paragraph P5). However...conditions for tropical development in these locations are not showing.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1928Z-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).

...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 from Greenland in the previous discussion is pushing into Europe...with cool air advection behind this cyclone enforcing a longwave upper trough covering the entire Atlantic high seas whose western upper convergence supports a 1021 mb ridge S of Greenland. E Canada deep-layered cyclone has decomposed into an upper trough and 1008 mb surface cyclone. Shortwave upper trough over the central US remains supported by cool air advection from frontal system diving in from W Canada...which is currently centered with a 1004 mb low in southern Hudson Bay. 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. T-storms have fired up SW of Bermuda in last 24 hrs...with support of divergent W Atlantic upper ridge...and from a satellite perspective appears to be associated with cold front of E Canada cyclone. The nearest surface trough to these t-storms has been analyzed west rather than under these t-storms...suggesting a system under westerly vertical shear of E Canada cyclone's upper trough. Therefore...no signs of tropical development are occuring here at this time.

P2...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 weakening to an east-west upper trough. A second and quiet elongated upper vortex is E of Bermuda. Central Caribbean inverted upper trough in previous discussion continues retrograding westward about W Atalntic upper ridge (paragraph P1). Third upper vortex SSW of the Azores has weakened into an upper trough south of the Azores in last 24 hrs.

P3...Atlantic surface ridge with 1020 mb to 1025 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...
P4...Upper ridging across Atlantic tropics remains concentrated into two areas. Upper ridge is in the western Caribbean has moved to SE Mexico...remaining supported by relatively higher pressures between the Gulf of Mexico upper vortex and central Caribbean inverted upper trough mentioned in paragraph P2. Tropical upper ridging remains firmly established in eastern tropical Atlantic.

P5...Tropical wave moved into eastern Pacific from SE Mexico in paragraph P6 of previous discussion....but t-storms have fired up right behind...starting over the Yucatan peninsula last evening and working there way into the SW Gulf of Mexico in last 24 hrs. I am not sure if these t-storms have association with this tropical wave...but a study of upper winds shows these t-storms started thanks to split flow upper divergence between SE Mexico upper ridge (paragraph P4) and Gulf upper vortex (paragraph P2). The SE Mexico upper ridge has inflated thanks to latent heat release of these t-storms...reducing the westerly shear from the Gulf upper vortex. However...surface pressures in the Gulf are high thanks to surface ridge discussed in paragraph P3...so there are no signs of tropical development in this area at this time.

P6...Remnant tropical wave of depression seven has entered the central Caribbean. Despite semi-favorable conditions described in special feature section of previous discussion #77...there are no signs of regeneration into a tropical cyclone...so I have dropped this as a special feature on this blog. As described previously...semi-favorable conditions continue to be from divergent west end of E Atlc tropical upper ridge (paragraph P4)... as well as reduced westerly shear thanks to vast upstream upper easterlies in the central Caribbean inverted upper trough (paragraph P2). Dry air to the west (origin of which mentioned in paragraph P3) is supported by upper convergence on the east side of SE Mexico upper ridge (paragraph P4). This system could outrun the favorable E Atlc tropical upper ridge...and into the much less favorable dry air and inverted upper trough. Atlernatively...this system could ingest the neighboring dry air if it spins up at the surface.

P7...Tropical wave Invest 93-L continues pushing west...and its large low pressure spin is centered 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 P4 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 P3).

P8...Tropical wave that emerged from Africa in previous discussion is now just E of the Cape Verde Islands...and continues to show disorganized t-storm activity despite the favorable environment provided by E tropical Atlc upper ridge mentioned in paragraph P4.

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