2012 Atlantic Hurricane Season Birdseye Discussion #20
...MAY 29 2012...9:28 PM EDT...
Threat of Beryl shifting into large section of Carolinas...SE Virginia...and SE Maryland south of the Delaware border. See special feature section for further details.
This is the twentieth birdseye discussion of the 2012 Atlantic Hurricane Season. See previous discussion #3 concerning the idea behind this new type of discussion forum.
...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 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).
...SPECIAL FEATURE...TROPICAL DEPRESSION BERYL...
Beryl will move NE from here on out while in southwesterly flow ahead of frontal system in paragraph P1. No change to the track forecast from the previous discussion...as the NHC forecast came into agreement with mine yesterday and the NHC has ever-since kept the track forecast the same. Albeit...Beryl is a bit behind in schedule from yesterday's track forecast...so the time points have been moved back a bit along the forecast track. Latest forecast for Beryl in Figure 2 below. NHC and computer models continue insisting that she will begin re-strengthening while taking advantage of frontal upper trough divergence associated with the system in paragraph P1. The status of Beryl will then become questionable as such a re-strengthening method is a non-tropical method. However...what supports Beryl being tropical during some of this duration is that very recently...some of the upper ridging in paragraph P2 is now directly overhead of Beryl. This upper ridging will allow Beryl to resemble a warm core structure in the upper-levels...where the upper ridge can ventilate the system like a tropical system. However...I expect Beryl to be fully non-tropical (extratropical) by Thursday.
Impact swath drawn in Figure 2 is based on recent radar structure shown in Figure 1. Notice now that the heaviest rains are now on the NE side of the center...something that we have been expecting thanks to shear from the incoming frontal upper trough of paragraph P1. The radar presentation in Figure 1 has forced me to expand the impact swath to now include north-central NC...SE Virginia...and Maryland (S of Delaware border). It should be noted that my impact swath yesterday did not include those areas. Rain and t-storms are occuring to the west of and outside my impact swath...in a band associated with the incoming frontal system in paragraph P1. In fact...this band is seen towards the upper-left side of the radar image in Figure 1. It should be noted my impact swath is focused exclusively on the spiral of Beryl...and not this band of t-storms (not associated with Beryl).
Figure 1: Radar image of Beryl taken at 7:15 PM EDT on May 29, 2012.
Figure 2: My current best-guess forecast for Tropical Depression Beryl.
P1...Frontal system in the central US is pushing into the eastern US at the expected pace...and therefore the NE track forecast for cyclone Beryl is essentially maintained from the previous discussion (see special feature section for details). Lowest surface pressure of this frontal system currently is 1002 mb over the W Great Lakes. Upper convergence on the west side of the system's upper trough supports some weak surface ridging tailing the system...such as the 1014 mb centers seen to the left side of the above charts...and the 1021 mb center in NE Montana.
P2...Central US upper ridge has broken into two fragments...one over Texas and northern Mexico...the second moving into the eastern US. This upper ridge continues to be supported by warm air advection ahead of frontal system in paragraph P1. Eastern convergence of this upper ridge system now supports the long-lived dry air in the Gulf of Mexico...Gulf of Mexico surface ridging...a 1021 mb ridge over the E coast of Canada...and another 1021 mb ridge center over Bermuda.
P3...See paragraph P8 of previous discussion #19 for how a few weather systems created a longwave upper trough regime across the entire high seas of the Atlantic. This longwave upper trough has an upper low vortex at its north end...and this entire longwave upper trough is cut-off to the south of the upper anticyclone in paragraph P4. At the surface...dominant feature is frontal system that was located in the high seas W of Greenland 24 hrs ago. It contained a 1005 mb center S of Greenalnd that has rapidly deepend to 988 mb as shown in the above charts. The rapid deepening was supported by split flow divergence between the upper low vortex (mentioned earlier in this paragraph) and upper anticyclone (mentioned in paragraph P4). Expect this 988 mb cyclone to whirl to a position beneath said upper low vortex...which will create a deep-layered low. On the south side of this emerging deep-layered low...a new 1004 mb frontal depression (marked in the above charts) is taking advantage of accelerational upper divergence and could intensify rapidly while moving ENE around the south side of the emerging deep-layered low.
P4...Full-fledged and anomalous upper anticyclone west of the British Isles continues. Days ago...its eastern convergence supported Atlantic surface subtropical ridging that has since weakened (due to the surface ridge separating from the upper convergence). Currently this weaker surface ridge consists of 1021 to 1019 mb centers SE of the weather system mentioned in paragraph P3.
...TROPICAL BELT DISCUSSION...
P5...Upper vorticity very near Tropical Depression Beryl has degenerated into a weak shortwave upper trough over the SE US. Upper convergence west of this shortwave (and east of the upper ridge in paragraph P2) supports long-lived sinking dry air across the Gulf of Mexico. As this shortwave upper trough gets absorbed by frontal upper trough mentioned in paragraph P1...responsibility of the Gulf dry air will shift to the upper ridge in paragraph P2. As discussed yesterday...upper divergence on the NE side of this vorticity had created a weak mid-level low pressure spin seen in satellite animations well E of Beryl that was heading east toward Bermuda. The mid-level low is not as defined from a satellite perspective today while it crossed Bermuda. Instead...it seems to live on as a shortwave upper trough over Bermuda at this hour. I believe this shortwave upper trough was caused when the mid-level low had advected in some of the upper vorticity very near Beryl. I expect this shortwave upper trough over Bermuda to move east and assimilate into the upper-levels of the weather system in paragraph P3.
P6...Long-lived Caribbean upper ridging persists. What's left of the embedded upper trough in this upper ridge is currently an upper vortex over the Yucatan and SE Mexico. See paragraph P10 of discussion #19 on how a tropical disturbance developed beneath this upper ridge. The surface trough of the disturbance was SW of Jamaica at 1200Z TAFB yesterday...and now is over the Yucatan at 1800Z TAFB tonight...as it seems the surface trough was steered west by Gulf of Mexico surface ridging mentioned in paragraph P2. Because the surface trough is now aligned with the upper vortex over the Yucatan...the system is analyzed as a deep-layered trough over the Yucatan in the above charts. The disturbance has not done what it needed to do for tropical cyclone devlopment...which was to maitain intense T-storm clouds to inflame the Caribbean upper ridging directly overhead of itself (to reduce vertical shear and enhance outflow). Now...the best of the caribbean upper ridging is found east of of the disturbance...and so the disturbance is in unfavorable southerly vertical shear E of the Yucatan deep-layered trough and W of the Caribbean upper ridge. Coincidentally...the southerly upper flow is also divergent...and so t-storms continue in the western Caribbean sea.
P7...Tropical wave that has been kept stationary (midway between Cape Verde Islands and Lesser Antilles) is finally moving westward in TAFB analyses...and will be reaching the Lesser Antilles soon. Currently...the tropical wave is in a hostile westerly vertical shear environment on the south side of weather system in paragraph P3.
P8...Upper ridge over the E tropical Atlantic continues.