2012 Atlantic Hurricane Season Birdseye Discussion #52
...JULY 15 2012...1:20 AM EDT...
Still watching to see if tropical wave develops in waters east of the Lesser Antilles...prior to reaching unfavorable upper winds (see paragraph P10). Otherwise...the Atlantic tropics remain calm.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0129Z-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...Central US surface frontal system has dissipated...but leaves behind its supporting upper trough. Another frontal system diving SE from western Canada has arrived to central Canada via Hudson Bay...and its upper trough has merged with the central US upper trough. Upper convergence behind the central US upper trough supports a surface 1018 mb ridge over the western US. Finally...warm air advection ahead of the Hudson Bay frontal system supports an upper ridge covering the eastern US and eastern Canada.
P2...Complex frontal system stretching from the SE US all the way toward Europe has consolidated in the north Atlantic south of Greenland. Upper trough heading toward Europe has made landfall....no longer in the scope of this blog. Upper trough that moved offshore from eastern Canada yesterday is now south of Greenland while supporting the 998 mb surface cyclone in the area. This surface cyclone has maintained strength in the past 24 hours...but now that it is beneath the less divergent axis of the upper trough...expect it to begin decaying.
P3...Cut-off upper vortex SW of the Azores persists. Cut-off upper trough over the Canary Islands is digging southward while orbiting the anticyclonic center of the upper ridge in paragraph P7...and as such this feature has been moved to paragraph P7.
P4...Open Atlantic surface ridge center has weakened from 1030 mb to 1028 mb in the last 24 hours. I had expected this weakening yesterday as the ridge center was beneath upper divergence on the NE quad of the upper vortex in paragraph P4. Now that the surface ridge center has relocated westward beneath the upper convergence on the NW quad of this upper vortex...expect the surface ridge to maintain strength. South side of this surface ridge is helping to waft Africa desert dry air westward across the Atlantic tropics.
...TROPICAL BELT DISCUSSION...
P5...Central America upper ridge now covers the south half of the Caribbean Sea.
P6...Caribbean area upper vorticity is dominated by large scale upper vortex that was N of the Caribbean Islands 24 hrs ago. Now...this large upper vortex is entering the southern Gulf of Mexico while retrograding about the east US upper ridge in paragraph P1. The eastern inflow of this upper vorticity diverges heavily with the western inflow of the cut-off upper vortex in paragraph P3...the divergence resulting in widespread cloudiness from near Bermuda all the way to western Cuba...and resulting in a new surface trough over Bermuda and the waters SW. There is also a new upper ridge just NE of Bermuda that separates this upper vorticity from the upper vortex in paragraph P3. E Gulf of Mexico 1015 mb low is tracking WNW into Louisiana while weakening into a surface trough...steered about the SW quad of the open Atlantic surface ridge (paragraph P4). Recently...this surface trough has been extended southward into the western Caribbean...perhaps caused by the divergent westerly jet between the upper vorticity discussed in this paragraph and upper ridge in paragraph P5. Alternatively...the southward extension of this surface trough may be the tropical wave from which this surface trough originated.
P7...East Atlantic upper ridge persists...still featuring an anticyclonic center WNW of the Cape Verde Islands. The embedded inverted upper trough on the south side has ejected westward about the anticyclonic center...and is now disorganized upper vorticity located toward the Lesser Antilles. The Canary Islands upper trough on the northeast side (paragraph P3) is moving southward about the anticyclonic center and toward the Cape Verde Islands.
P8...Tropical wave approaching the Lesser Antilles in the previous discussion has crossed the islands into the eastern Caribbean. It is suppressed by westerly vertical shear induced by the upper vorticity mentioned in paragraph P6.
P9...Tropical wave midway between the Cape Verdes and Lesser Antilles is speeding westward toward the Lesser Antilles. The western side of the tropical wave is suppressed by dry air mentioned in paragraph P4. Surface convergence on the east side of the the tropical wave...coupled with enhanced poleward upper outflow (induced by west flank of upper anticyclonic center trough in paragraph P7)...is creating a moist air buffer seen in the above thermo birdseye chart.
P10...Satellite animation suggests the tropical wave SE of the Cape Verde Islands in the previous discussion is now SW of the islands. This is the second time I have analyzed this wave in the above birdseye charts while the NHC TAFB maps have yet to acknowledge it...but I am confident that the tropical wave exists. Satellite animation suggests the t-storms of the tropical wave have been squashed into its south half...and the t-storms have become less distinguishable within an east-west ITCZ band. This tells me the tropical wave has been affected by northerly shear on the east flank of the upper anticyclone in paragraph P7...and this shear has also allowed the dry air in paragraph P4 to intrude into the north half of the tropical wave. However...there is still a moisture buffer west of the tropical wave as explained at the end of paragraph P9...and the GFS model still suggests the upper anticyclone in paragraph P7 will be pushed southward by a merger between the cut-off upper vortex in paragraph P3 and upper trough in paragraph P2. The southward displacement of this upper anticyclone would enhance the upper outflow of the tropical wave. Moreover...the GFS model suggests this upper anticyclone should shift westward...thanks to Canary Islands upper trough (paragraphs P3 and P7) digging southward toward the Cape Verde Islands. Because model runs do not show this upper anticyclone expanding westward beyond the Lesser Antilles...I think this tropical wave has a chance to become a tropical disturbance (such as an "Invest" on the Navy NRL site)...or at most a weak tropical cyclone...while it is east of the Lesser Antilles. Beyond that...it looks like unfavorable upper winds will stop this wave from developing.
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