2012 Atlantic Hurricane Season Birdseye Discussion #51
...JULY 14 2012...12:50 AM EDT...
While tropical development is no longer expected in the eastern Gulf of Mexico (paragraph P7)...next tropical wave emerging from Africa has potential to develop (paragraph P11).
...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).
P1...Frontal system from central Canada has dived SE into the central US. Its supporting upper trough has merged with central US upper trough from paragraph P3...and the central US upper trough looks to be re-enforced by cool air advection from another frontal system diving SE from western Canada. Upper convergence behind the central US upper trough supports a surface 1017 mb ridge over the western US. Finally...warm air advection ahead of the central US frontal system supports an upper ridge wave that has moved into the eastern US and merged with Florida upper ridge in paragraph P7.
P2...North Atlantic upper ridge has merged with east tropical Atlantic upper ridge in paragraph P8.
P3...Complex frontal system stretching from the SE US all the way toward Europe persists. Upper trough heading toward Europe is approaching landfall. Upper trough over eastern Canada has moved offshore while its eastern divergence has strengthened the northwest Atlantic surface cyclone to 998 mb as of 1930Z...and its western convergence supports a 1019 mb ridge over E Hudson Bay and 1025 mb ridge over the NE US. The central US upper trough is now part of frontal system discussed in paragraph P1.
P4...Cut-off upper vortex SW of the Azores has stalled with the dissipation of the steering upper ridge in paragraph P2. Cut-off upper trough over the Canary Islands persists.
P5...Open Atlantic surface ridge still has a strong center...1031 mb SW of the Azores as of 1800Z. It is now beneath upper divergence on the NE quad of the upper vortex in pagragraph P4...so this surface ridge is likely to weaken some in the next 24 hours. South side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.
...TROPICAL BELT DISCUSSION...
P6...Central America upper ridge persists...with a divergent anticyclonic center over the Panama area enhancing t-storms below.
P7...Caribbean upper vorticity has merged with large upper vortex N of the Caribbean Islands in paragraph P8. The eastern inflow of this upper vorticity diverges heavily with the western inflow of the cut-off upper vortex in paragraph P4...the divergence resulting in widespread cloudiness south of Bermuda. This upper vorticity still extends to an upper low in the southern Gulf of Mexico. As the upper vortex N of the Caribbean Islands moves westward toward upper vortex in the south Gulf...the Florida upper ridge has been pushed northward such that it has merged with the upper ridge mentioned in paragraph P1. Surface tropical wave in the area has moved into the eastern Gulf of Mexico while maturing into a 1015 mb low thanks to upper divergence supplied by Florida upper ridge. The 1015 mb low is tracking WNW toward the US Gulf coast about the SW quad of the 1025 mb surface ridge (paragraph P3) and open Atlantic surface ridge (paragraph P5). With the 1015 mb low soon to move over land and moving away from the divergent core of the Florida upper ridge...tropical cyclone development is not possible.
P8...Large scale upper vortex north of the Caribbean Islands has merged with Caribbean area upper vorticity mentioned in paragraph P7. Behind this...the east Atlantic upper ridge has rebuilt from western Africa...now featuring an anticyclonic center present WNW of the Cape Verde Islands and embedded inverted upper trough west of the Cape Verde Islands.
P9...Tropical wave midway between the Cape Verde Islands and Lesser Antilles in previous discussion is approaching the Lesser Antilles. It still features a surface low on its south end that has weakened to 1010 mb. It has exited the unfavorable dry air mentioned in paragraph P5...but is now entering the unfavorable westerly vertical shear induced by the upper vorticity mentioned in paragraph P7. A southwesterly jet on the SE flank of this upper vorticity may enhance the poleward upper outflow of this tropical wave...so some shower or t-storm activity is possible as the tropical wave crosses the Lesser Antilles in the next 24 hours.
P10...Tropical wave over the Cape Verde Islands in the previous discussion has moved quickly west to the waters midway between the Cape Verdes and Lesser Antilles. The western side of the tropical wave is suppressed by dry air mentioned in paragraph P5. Surface convergence on the east side of the the tropical wave...coupled with enhanced poleward upper outflow (induced by east flank of inverted upper trough in paragraph P8)...has significantly increased t-storm activity SW of the Cape Verde Islands.
P11...Satellite imagery suggests the next tropical wave had just rolled off of Africa...and is currently SE of the Cape Verde Islands. It has a decent structure with good spin and t-storm bursts on satellite animation. The tropical wave in paragraph P10 is producing a large area of t-storms SW of the Cape Verde Islands that is protecting this tropical wave from the dry air in paragraph P5. Moreover..a gander at the GFS model suggests the upper winds could become favorable thru the next 72 hours...so this tropical wave appears to have potential to become a tropical cyclone. The GFS model suggests that the anticyclonic center of the paragraph P8 upper ridge will be pushed southward by a merger between the cut-off upper vortex in paragraph P4 and east Canada upper trough in paragraph P3. The southward displacement of this upper anticyclonic center would enhance the upper outflow of the tropical wave. Morover...the GFS model suggests this anticyclonic center should shift westward with the tropical wave...thanks to Canary Islands upper trough in paragraph P4 forecast to dig southward toward the Cape Verde Islands.