2012 Atlantic Hurricane Season Birdseye Discussion #26
...JUNE 12 2012...10:57 PM EDT...
Tonight...watching NW Atlantic for possible subtropical cyclone development. Caribbean Sea activity is increasing. See paragraphs P2 and P6 for further details on these situations.
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1924Z-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...Strong surface frontal cyclone persists over Canada's Hudson Bay...still supported by divergence ahead of vigorous central US upper trough. Convergence behind central US upper trough supports a 1024 mb ridge marked in the above charts. 1017 mb low in W North Carolina has weakend to a SE US pre-frontal surface trough in last 24 hrs. Warm air advection ahead of Hudson Bay frontal cyclone supports east US upper ridge that extends along the Gulf coast. Westerly flow at the base of the central US upper trough diverges with northerly flow across Gulf coast portion of upper ridge...this divergence supporting surface lows of 1014 mb (N Texas) and 1017 mb (LA/MS/AK border)...along the cold front extending far from the Hudson Bay cyclone. The upper ridge's eastern convergence supports surface 1022 mb centers offshore of Atlantic Canada.
P2...Upper vortex in NW Atlantic persists...and remains stacked above 1010 mb frontal low. Accelerational divergence SE of this upper vortex still supports a bare surface front across the central Atlantic...a fragment of which has decayed into a surface trough over the central Bahamas. This surface trough may merge with N end of Caribbean Sea tropical wave (mentioned in paragraph P6 below). The 1010 mb frontal low below the upper vortex has begun firing convective cloudiness...perhaps as the upper vortex is cold enough to de-stabilize the atmosphere despite waters of 23 deg C. Albeit...I would like to see convective cloudiness fire much closer to the center than currently seen to more seriously consider this a candidate for subtropical development. If convective cloudiness does not improve from current structure in the next 24 hours...I will be calling off this area for subtropical development.
P3...Deep-layered anticyclone S of the Azores (with surface center of 1030 mb) has vertically re-coupled.
...TROPICAL BELT DISCUSSION...
P4...In yesterday's discussion (paragraph P1)...upper trough associated with Hudson Bay cyclone was absorbing an old central US upper trough. What has not been absorbed is across the Gulf of Mexico tonight.
P5...East-west upper trough remains across the Caribbean Sea. Upper vorticity midway between the Lesser Antilles and Azores persists. Remainder of the dry air in the tropical belt at this time has collected beneath both these upper features...when looking at tonight's thermodynamic birdseye chart.
P6...Long-lived Caribbean upper ridging persists...currently forked in half by east-west upper trough of paragraph P5. The northern half is an upper anticyclone over Cuba...the southern half is an upper anticyclone near Panama which continues to fire strong t-storms over the surface ITCZ in the area. Tropical wave that was over the Lesser Antilles yesterday (discussion #25 paragraph P9) is zooming west across the Caribbean and may add fuel to the disturbed weather beneath the Panama upper anticyclone. If so...the Panama upper anticyclone would intensify via latent heat release of the t-storm activity...and in turn the upper anticyclone would aid in outflow for surface pressure falls and tropical development. Considering computer models have wanted to flare up the upper anticyclonicity in this region (and develop a tropical cyclone beneath it)...we will be watching this carefully. To be honest...the models have wanted to develop this tropical cyclone activity no sooner than June 18...almost suggesting that tonight's Panama upper anticyclone/surface tropical wave pair is not what the models have been developing. The GFS model solution for future Caribbean tropical activity is complex tonight...suggesting that the upper trough in paragraph P1 and upper vortex in paragraph P3 merge..afterwards the merger leaving behind an upper vortex offshore of SE US that entagles itself with a 1st tropical-to-subtropical cyclone that tracks from the Caribbean to Bahamas (June 18 to 20 timeframe). The GFS then develops a 2nd Caribbean tropical cyclone that tracks into the Bay of Campeche (June 20 to 24 timeframe).
P7...Upper ridge in E tropical Atlantic continues to keep air moist in the area thanks to its upper outflow.
P8...Tropical wave passing S of the Cape Verde Islands 24 hrs ago is WSW of those islands tonight. It has left the favorable upper ridge mentioned in paragraph P7...entering less favorable dry air and westerly vertical shear associated with features in paragraph P5 above.