2012 Atlantic Hurricane Season Birdseye Discussion #28
...JUNE 15 2012...12:20 AM EDT...
As far as tropical cyclone activity is concerned...all clear in the Atlantic tonight.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1923Z-released HPC analysis.
In light blue is upper air anlaysis, 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 indicating surface lows, Hs indicating 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 cyclone from SW Canada continues east...and associated upper trough is moving across the western US tonight. Warm air advection ahead of this frontal system has generate a new shortwave upper ridge over the W Great Lakes. Cold front extending from SW Canada cyclone is pushing across the central US with associated severe t-storms.
P2...Shortwave upper trough has moved from the central US into the SE US in the last 24 hours. Divergence ahead of this upper trough now supports a 1014 mb frontal low over the AL/GA border...and a 1010 mb frontal low SE of Virginia...both frontal features left behind by old Hudson Bay system as mentioned in paragraph P3 below.
P3...Surface frontal cyclone that was over Canada's Hudson Bay has left behind several features. In the upper-levels...an upper trough is over E Canada (once caused by the cyclone's cold air advection) and upper ridge is over the W Atlantic (once caused by the cyclone's warm air advection). Convergence behind the E Canada upper trough supports 1030 mb center below and a 1028 mb center exiting Michigan. Convergence ahead of W Atlantic upper ridge supports 1030 mb center S of Greenland. Finally...this Hudson Bay cyclone had left behind a decaying front with a 1006 mb low over E Canada and 1009 mb low offshore of Virginia. The 1006 mb low is now 1010 mb but supported by divergence ahead of E Canada upper trough. The 1009 mb low offshore of Virginia is now 1010 mb...and the decaying front has yet another low of 1014 mb at the AL/GA border. Both the 1010 and 1014 mb lows are now associated with upper trough mentioned in paragraph P2 above.
P4...Upper vortex in NW Atlantic persists...and remains nearly stacked with 1009 mb low in the above charts. The Bahamas surface trough left behind by this system has been cancelled in NHC TAFB analyses...and the associated leftover clouds are pulling NE away from the Bahamas while associated with divergence on the back side of W Atlantic upper ridge (mentioned in paragraph P3 above). I stopped considering the 1009 mb surface low a threat for subtropical cyclone development in my previous discussion. However...it is interesting to note that the NHC dropped all fronts attached to the 1009 mb low in the recent 1800Z TAFB analysis as if it is less non-tropical. I still do not expect subtropical development as the convective cloudiness refuses to improve...and the thermodynamic picture gets less favorable with time as the 1009 mb low is forecast to track ENE toward even cooler waters.
P5...Deep-layered anticyclone S of the Azores has vertically de-coupled...with the upper anticyclonic center moving ENE while becoming associated with warm air advection ahead of system in paragraph P6 below. Surface 1026 mb center S of the Azores remains at this location and has weakened to 1025 mb in the last 24 hours.
P6...Relatively new upper trough persists in the NE Atlantic...supported by cold air advection behind the strengthening surface cyclone it has manifested with divergence E of the upper trough axis. This surface extratropical (non-tropical) low is not in the scope of TAFB nor HPC analyses...so I am using satellite imagery to fix the position of this low in the above charts. This surface low is moving into W Europe...and appears vigorous based on its satellite organization.
...TROPICAL BELT DISCUSSION...
P7...Upper trough in the Gulf of Mexico is absorbed by upper trough mentioned in paragraph P2 above.
P8...I forecasted in discussion #27 pargraph P10 that the Panama upper anticyclone (in the Caribbean) would shift west over the building latent heat release of eastern Pacific TD 3-E (which is now TS Carlotta)...and in turn shearing upper northwesterlies would spread across the Caribbean in the wake of the exiting upper anticyclone. Instead...Carlotta has built a seperate upper anticyclone overhead while the Panama upper anticyclone has remained stationary...and a new Yucatan upper trough has formed between the two upper anticyclones. Despite this deviation from my forecast...vast shearing upper westerlies still have developed outside of these upper anticyclones...and the Caribbean Sea tropical wave following behind Carlotta stands no chance of developing beneath this shear. This could be a particularly dangerous situation for the S coast of Mexico as E-Pac TS Carlotta continues to strengthen beneath its upper anticyclone...and get steered NW toward the area by the Panama upper anticyclone. As Carlotta and its upper anticyclone shift northward & closer to the Atlantic side of things...computer models still want to take advantage by expanding said upper anticyclone and develop a tropical cyclone below it in the Bay of Campeche beginning June 20. As we get closer to the June 20 timeframe thru this week...it will become clearer exactly how (or even if) this situation plays out.
P9...In discussion #27 paragraph P10...a new central Caribbean upper trough was briefly mentioned...which developed in the wake of the upper anticyclones discussed in paragraph P8 above. This upper trough has shifted ENE into the NE Caribbean while gravitated toward the upper vortex mentioned in paragraph P4 above.
P10...Upper ridge in E tropical Atlantic has finished reversing into an upper vortex. This reversing occurred as the upper-levels of anticyclone to the north (in paragraph P5) gained strength from warm air advection. The upper vorticity midway between the Lesser Antilles and Azores (discussion #27 paragraph P8) has been absorbed into this new E Atlantic upper vortex.
P11...Upper ridging persists south of the paragraph P4 1009 mb deep-layered cyclone (where upper-level pressures are relatively higher)...located across the E Caribbean and central tropical Atlantic.
P12...Tropical wave continues approaching the Lesser Antilles tonight...but is under a hostile westerly shear enivronment on the north side of the upper ridge mentioned in paragraph P11 above. Cloud cover already exists over the Lesser Antilles and ahead of this tropical wave...thanks to upper divergence ahead of upper trough in paragraph P9. As the tropical wave interacts with this upper divergence...weather activity over the Lesser Antilles is bound to increase.
P13...Tropical wave that emerged western Africa last evening is S of the Cape Verde Islands tonight. Since the E Atlantic is now covered by an upper vortex (as explained in paragraph P10 above)...upper winds will be unfavorable for this tropical wave to develop.
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