2012 Atlantic Hurricane Season Birdseye Discussion #50
...JULY 13 2012...12:40 AM EDT...
Tropical cyclone development in the eastern Gulf of Mexico looking less likely. See paragraph P7 for details.
...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...Frontal system from western Canada is moving into central Canada. Warm air advection ahead of this system supports an upper ridge wave over central Canada...while the upper ridge over the western US once supported by the same warm air advection is left behind.
P2...North Atlantic upper ridge persists via support of southwesterly warm air advection ahead of complex frontal system discussed in paragraph P3.
P3...Northwest Atlantic surface cyclone and its supporting longwave upper trough have degenerated into a less organized...complex frontal system stretching from the SE US all the way toward Europe. At the surface...the northwest Atlantic surface cyclone is diffuse with multiple low pressure centers on the east coast of Canada...in the vicinity of Greenland...and heading into western Europe. There are also surface frontal depressions in the western Atlantic and SE US supported by eastern divergence of the longwave upper troughing. The longwave upper troughing has decomposed into one trough heading toward Europe...another over east Canada...and a third over the central US. Upper convergence on the back side of the longwave upper troughing supports a 1017 mb surface ridge over E Hudson Bay...1022 mb ridge over the Great Lakes...and 1017 mb ridge over the SW US.
P4...Northeast Atlantic upper trough has moved into Europe...but leaves behind a cut-off upper vortex SW of the Azores retrograding westward about the upper ridge in paragraph P2...and a cut-off upper trough over the Canary Islands.
P5...Open Atlantic surface ridge still has a strong center...1032 mb SW of the Azores as of 1800Z...now supported by upper convergence between southerlies (on the NE flank of the cut-off upper vortex in paragraph P4) and easterlies (on the south side of the upper ridge in paragraph P2). In conjunction with upper ridge in paragraph P2...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 and northern South America upper ridge persists...with divergence on its southwest side supporting t-storm activity over the Panama area.
P7...Caribbean upper vorticity has elongated into a few features while wedged between the Central America upper ridge in paragraph P6 and North Atlantic upper ridge in paragraph P2. This upper vorticity still extends to an upper low in the southern Gulf of Mexico...while its upper trough near the Bahamas has been absorbed by incoming upper vortex mentioned in paragraph P8. There is still a divergent Florida upper ridge separating the south Gulf upper vortex from the incoming vortex in paragraph P8...but the mid-level low and tropical wave below have not taken much advantage of the upper ridge as they both push into the eastern Gulf of Mexico (sat imagery suggests the mid-level low is moving west over Tampa and heading into the Gulf). The tropical wave and mid-level low are now running out of time to develop beneath the Florida upper ridge before moving into the less favorable environment beneath the south Gulf upper vortex. NAM model still suggests tropical development...and tracks it WNW toward the Louisiana coast about the SW quad of the Great Lakes surface ridge (paragraph P3) and open Atlantic surface ridge (paragraph P5). GFS model still shows no tropical development.
P8...Large scale upper vortex from the eastern Atlantic is ejecting westward and passing north of the Caribbean Islands while retrograding about the upper ridge in paragraph P2. The eastern inflow of this upper vortex diverges heavily with the western inflow of the cut-off upper vortex in paragraph P4...the divergence resulting in widespread t-storm activity across the eastern semicircle of this upper vortex. Behind the retreating upper vortex...the east Atlantic upper ridge is rebuilding from western Africa.
P9...Tropical wave midway between the Cape Verde Islands and Lesser Antilles still features a 1008 mb surface swirl on its south end...and is still suppressed by dry air mentioned in paragraph P5. Outside of the dry air...the immediate environment of this tropical wave is favorable for development thanks to low shear on the south side of the rebuilding east Atlantic upper ridge in paragraph P8. However...I still expect the tropical wave to eventually encounter westerly vertical shear on the south side of the upper vortex also mentioned in paragraph P8.
P10...Tropical wave that has recently emerged from Africa is marked over the Cape Verde Islands as of 1800Z TAFB analysis. If the tropical wave in paragraph P9 is a good analogue...expect this tropical wave to become suppressed by dry air.