2012 Atlantic Hurricane Season Birdseye Discussion #79

By: NCHurricane2009 , 10:30 AM GMT on August 15, 2012

...AUGUST 15 2012...6:31 AM EDT...
Remnant of tropical depression seven is currently crossing Central America and the western Caribbean. Land interaction with Central America is preventing this system from regenerating into a tropical cyclone...but it could reemerge into the Bay of Campeche and western Gulf of Mexico in the next days. See paragraph P5 for details.

Elsewhere...tropical wave Invest 93-L has rapidly organized in the last 24 hours...and is at high risk of tropical cyclone formation in the next 24 hours. Interests in the Azores should monitor the progress of 93-L as computer models suggest it near or just south of the area in the next days. See special feature section below for further details.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-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.


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).

Low pressure spin of tropical wave Invest 93-L has arrived to the waters NE of the Lesser Antilles. Finally...the favorable upper outflow beneath paragraph P4 E Atlc upper ridge...coupled with increased instability over increasingly warm waters...has allowed this system to overcome dry air(source of dry air mentioned in paragraph P3). The low pressure spin has rapidly organized in the last 24 hrs with increasing spiral bands...and is likely to become a tropical cyclone anytime in the next 24 hrs.

Short-term motion of this low pressure center is straight NW according to Figure 1...as it is currently recurving into a large-scale deep-layered ridge weakness caused by upper vorticity in paragraph P2...and caused by surface frontal and upper troughal activity in paragraph P1. This NW track should allow this system to safely pass east of Bermuda. Computer model consensus shown on www.wunderground.com/tropical has a good grip on the short-term NW motion...but I specifically prefer the models that show a track passing a little west of 55W-30N rather than over 55W-30N (due to the angle of current short-term motion). In the longer-range...the computer model consensus leans toward a recurving track that would take it south of the Azores rather than over the Azores...but interests in the Azores should watch this system.

Figure 1: Short term motion of tropical surface low Invest 93-L this morning based on 0045Z and 0745Z center fixes using satellite imagery.

P1...Upper trough regime over central US and central Canada has spread into eastern areas and all of the Atlantic high seas. Frontal cyclone heading into Europe in the previous discussion has made landfall...and yet another frontal cyclone has spun up along the cold front of this frontal cyclone. This new and rapidly developing frontal cyclone is also heading into Europe. Cool air advection behind these cyclones continues enforcing a longwave upper trough covering the entire Atlantic high seas...whose western upper convergence supports a 1024 mb ridge SW of Greenland. E Canada surface cyclone has decayed into surface troughs and east-west front across the northwest Atlantic....with its shortwave upper trough passing south of Greenland. Shortwave upper trough over the central US is pushing into the eastern US...supported by cool air advection from frontal system diving in from W Canada...currently centered with a 1007 mb low in southern Hudson Bay. Low-level warm air advection ahead of this 1007 mb cyclone supports W Atlantic upper ridge...while SW US upper ridge persists behind this regime.

P2...Mid-ocean upper vorticity persists. One upper vortex persists in the Gulf of Mexico. Elongated upper vortex E of Bermuda has weakened into an upper trough reaching into the north-central Caribbean. Central Caribbean inverted upper trough has dissipated due to tremendous latent heat release from the remnants of tropical depression seven (paragraph P5).

P3...Atlantic surface ridge with 1019 mb to 1024 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 sides of W Atlantic upper ridge (paragraph P1) and E Atlantic upper ridge (paragraph P4)...south side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.

P4...Upper ridge across the eastern tropical Atlantic has grown into the east half of the Caribbean.

P5...Remnant tropical wave of depression seven has entered the western Caribbean and Central America. Due to high split flow upper divergence between the E Atlc tropical upper ridge (paragraph P4) and W Atlantic upper ridge (paragraph P1)...this system has developed a significant increase in size and intensity of t-storm activity. Latent heat release from the t-storm activity has punched out the unfavorable central Caribbean inverted upper trough (paragraph P2)...and moisture from the t-storm activity has eradicated the dry air in the area (source of dry air in paragraph P3). Despite all of this...tropical cyclone reformation is prevented currently by land interaction with Central America. Beginning 90 hrs from now...GFS computer model has been insisting that the remnants could eventually contribute to tropical cyclone formation in the Bay of Campeche/western Gulf of Mexico. GFS shows the tropical cyclone curving slowly NW toward S Texas/NE Mexico thru 183 hrs from now...steered about the SW quad of a low-level ridge that builds behind a frontal system (this frontal system is not yet in the scope of the above charts...but will soon enter from the upper-left of the charts in next 24 hrs).

P6...Tropical wave Invest 93-L is currently NE of the Lesser Antilles. Due to its high potential for tropical cyclone formation in the next 24 hrs...it has been moved to its own special feature section above. See special feature section above for further details on this system.

P7...Tropical wave E of the Cape Verde Islands in the previous discussion is now west of the islands...and continues to show disorganized t-storm activity despite the favorable environment provided by E tropical Atlc upper ridge mentioned in paragraph P4. On the other hand...dry air is just to the northwest of this tropical wave (source of dry air mentioned in paragraph P3). For now...this dry air is likely to stall any development potential with this tropical wave.

P8...Satellite imagery suggests the next tropical wave is emerging from west Africa into the tropical belt of the Atlantic (see lower-right corner of above atmo chart).

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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