2012 Atlantic Hurricane Season Birdseye Discussion #58
...JULY 21 2012...2:08 AM EDT...
Watching the next tropical wave emerging from Africa (see paragraph P11). Pop-up disturbance in northern Gulf of Mexico...near Louisiana and Mississippi...does not appear to have tropical development potential (paragraph P6).
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1934Z-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).
P1...Next surface frontal system and upper trough in mid-latitude westerlies is entering the birdseye charts from the upper-left corner...moving into central Canada. Warm air advection ahead of this frontal system has created an upper ridge over eastern Canada.
P2...Vigorous frontal cyclone south of Greenland is maintained by divergence east of a sharp upper trough pushing offshore from eastern Canada...and is 987 mb as of 1934Z. Upper convergence behind the sharp E Canada upper trough supports a 1022 mb ridge over the Great Lakes and E Canada. Upper anticyclone over the SW US has grown into the western US behind the sharp E Canada upper trough. Cold front trailing from the 987 mb cyclone has a frontal depression and its supporting upper trough embedded...which has traveled from Michigan into the Ohio Valley in the last 24 hours.
P3...Cut-off upper vortex south of Bermuda has weakened into an upper trough in the last 24 hours...compressed between the Bermuda-area upper ridge in paragraph P6 and east Atlantic upper ridge in paragraph P7.
P4...Open Atlantic surface ridge is supported by a few upper convergent sources this early morning. Convergence south of the western US upper anticyclone (paragraph P2) supports 1020 to 1021 mb centers over the SW US and Gulf of Mexico. Convergence SE of Bermuda-area upper ridge (paragraph P6) supports a 1024 mb center east of Bermuda. Convergence behind the Canary Islands upper trough (paragraph P7) supports a 1027 mb center just south of the Azores. In conjunction with the south side of the upper ridge in paragraph P7...south side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.
...TROPICAL BELT DISCUSSION...
P5...Upper ridge over the south Caribbean Sea currently covers Central America as a wave. Divergence west of this upper ridge wave supports t-storm activity over Panama and Costa Rica.
P6...Upper vorticity in the southern Gulf of Mexico is weakening over the Yucatan and SE Mexico....and leaves behind upper vortex over the SC/GA border that has recently weakened into a SE US upper trough. Bermuda-area upper ridge persists east of all this upper vorticity. T-storm activity continues to flourish over the MS/LA area with surface trough formation...all supported by split flow divergence at the boundary between the SE US upper trough and west US upper anticyclone (paragraph P2). Latent heat release from the t-storm clouds appears to be inflating the south lobe of the west US upper anticyclone such that the disturbance is developing upper anticyclonic outflow similar to a tropical system. However...land interaction and high surface pressures from the paragraph P4 ridge limit tropical development potential. Expect SE US upper trough to merge with Ohio valley upper trough in paragraph P2...reducing the split flow upper divergence between the SE US upper trough and west US upper anticyclone supporting this weather. Therefore...if this disturbed weather loses aforementioned latent heat release driven upper outflow...it will then quickly succumb to upper convergence on the south side of west US upper anticyclone and dissipate. In the meantime...radar shows rainfall pushing out of MS/LA and toward SE Texas...while S MS and SE LA have flood advisories due to previous rainfall from this system.
P7...East Atlantic upper ridge persists. Upper vorticity is still west of the upper ridge...located in the central Caribbean Sea. This upper ridge remains dwarfed in half by Canary Islands upper trough...the western half amplifying via warm air advection ahead of paragraph P2 frontal system...the east half located toward Africa. Amplification of west half of this upper ridge is causing amplification of the Canary Islands upper trough.
P8...Tropical wave moving across SE Mexico in the previous discussion has moved into the eastern Pacific and outside the scope of the above charts. This is the last statement on this tropical wave on this blog.
P9...Tropical wave in the eastern Caribbean Sea in the previous discussion is pushing into the central Caribbean. Surface convergence east of this tropical wave axis...coupled with split flow upper divergence between the east side of the central Caribbean upper vortex and east Atlantic upper ridge (paragraph P7)...has caused t-storm activity to develop across Puerto Rico...Hispaniola...and Jamaica in the last 24 hours.
P10...Tropical wave midway between the Cape Verde Islands and Lesser Antilles in the previous discussion is approaching the Lesser Antilles. This tropical wave still has an impressive structure with a cyclonic turning of faint clouds still visible on satellite...but its t-storm activity is limited by the fact it is below non-divergent uniform easterly flow on the south side of the upper ridge in paragraph P7. The above thermo birdseye chart suggests the NW half of its cyclonic flow has ingested dry air mentioned in paragraph P4...while the SE half still has moisture.
P11...Satellite imagery suggests an impressive tropical wave (with t-storms and organized low pressure spin) has rolled off of Africa. Dry air (mentioned in paragraph P4) has been a problem for the past several tropical waves...so it is uncertain if this tropical wave will develop despite an impressive structure. GFS computer model shows no development with this tropical wave...but a study of its upper wind forecast suggests potentially favorable conditions for development. Canary Islands upper trough is currently amplifying as described in paragraph P7...and the GFS model breaks off an upper vortex from the amplifying trough that retrogrades westward about the west half of the upper ridge in paragraph P7. If this tropical wave phases properly with the forecast upper vortex...the upper vortex could enhance the northwestern upper outflow of this tropical wave in the coming days. The upper vortex is later forecast to stall while merging with the upper trough in paragraph P1...and also is forecast to leave behind upper vorticity in the Caribbean Sea and ahead of the tropical wave. Therefore...if the tropical wave does not develop east of the Caribbean Sea due to dry air...it will later encounter unfavorable upper winds as it catches up to the stalling upper vorticity.
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