2012 Atlantic Hurricane Season Birdseye Discussion #19
...MAY 28 2012...4:55 PM EDT...
Beryl inland near the Florida-Georgia border and has weakened to a tropical depression. Watching new disturbance in the western Caribbean Sea. See special feature section and paragraph P10 in tropical belt discussion for further details.
This is the nineteenth 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 1200Z, and the 1321Z-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...
Not a whole lot to say about Beryl today...since it pretty much followed both the track and intensity forecast I presented in the previous discussion. For the NE recurvature forecast...I was a bit left of yesterday's NHC's track based on the timing of the frontal system mentioned in paragraph P1 below. The frontal system's timing remains on cue...and today's NHC forecast track has "dead-nuts" lined up with the track I presented yesterday...so my updated track forecast in Figure 1 below is a continuation of the previous. Beryl weakened a tad faster than I forecasted...so I am now expecting a 30 mph remnant low by 11 PM tonight instead of by 11 AM Tuesday. I still have some re-strengthening after 11 AM Tuesday as the NHC and computer models insist that the frontal upper trough recurving her NE will supply some supportive upper divergence...so the status of Beryl is questionable during the NE recurvature as such a re-strengthening method is a non-tropical (extratropical) method.
Diameter of blue-dashed impact swath in Figure 1 is based on the current diameter of the spiral rain shield seen on radar. The impact swath diameter I drew in during the NE-recurvature today is larger than the drawn-in diameter during NE-recurvature yesterday. This is because I am a bit surprised how far out the spiral rain bands from Beryl are reaching on current radar...but the gusty winds can only be near the center of Beryl...or in any severe T-storms that Beryl produces. I expect this rain shield will eventually get distorted to a bias E of center as the incoming frontal upper trough shears Beryl. However...with a NE track also expected...the impact swath remains symmetric about the forecast track.
Figure 1: My current best-guess forecast for Tropical Depression Beryl.
P1...Frontal system from the western US is ejecting eastward into the central US at the expected pace...and therefore the NE recurvature forecast for cyclone Beryl is maintained from the previous discussion (see special feature section for details). Lowest surface pressure of this frontal system currently is 1000 mb in SE Manitoba. Upper convergence on the west side of the system's upper trough supports a 1020 mb surface ridge in N Utah.
P2...Central US upper ridge continues to be supported by warm air advection ahead of frontal system in paragraph P1. This upper ridge is now quiet expansive...and extends eastward into the NW Atlantic. Eastern convergence from this upper ridge supports a plethora of surface ridging...including a 1015 mb center in SW Louisiana...1019 mb center in N Virginia..and 1023 mb center near Bermuda.
P3...A frontal system has entered the high seas W of Greenland as expected 24 hrs ago...but further east progression is being halted by an anamalous full-fledged upper anticyclone mentioned in paragraph P6. Its upper trough supports a 1005 mb center S of Greenland with eastern divergence...and supports a 1027 mb center over S Hudson Bay with western convergence. We were discussing a southern fracture of this upper trough 24 hrs ago...which continues SE into the open Atlantic at a position E of Bermuda.
P4...Upper vortex NW of the Azores continues to support a less-than-1012 mb surface frontal cyclone...and is cut-off to the south of anamalous upper anticyclone in paragraph P6. The cold front attached to the frontal cyclone is decaying rapidly...and leaves behind a surface trough just NE of a 1023 mb ridge center as shown in the above charts.
P5...Upper vortex located well NE of the Lesser Antilles 24 hrs ago has moved eastward to a position NW of the Cape Verde Islands...where it has weakened to an upper trough...and where its eastern divergence is producing a comma shaped cloud mass.
P6...Full-fledged upper anticyclone west of the British Isles continues to be associated with warm air advection ahead of frontal system in paragraph P3. 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 1023 mb centers SE of the less-than-1012 mb cyclone in paragraph P4.
P7...Deep-layered non-tropical low continues spinning on satellite to the SW of the British Isles as marked in the upper-right corner of the above charts...trapped on the south side of the upper anticyclone mentioned in paragraph P6.
P8...The weather systems in paragraphs P3...P4...P5...and P7 are beginning to create a longwave upper trough regime that spreads across the entire high seas of the Atlantic. Accelerational divergence on the east side of this emerging regime appears to have created a 1011 mb surface depression over Spain as marked in the above charts and 1200Z TAFB.
...TROPICAL BELT DISCUSSION...
P9...Upper vorticity remains trapped offshore of SE US and E Gulf of Mexico...and is located very near Tropical Depression Beryl. Upper convergence west of this vorticity (and east of the upper ridge in paragraph P2) supports long-lived sinking dry air across the Gulf of Mexico. Upper divergence between the NE side of this vorticity and mainstream upper westerlies has created a weak mid-level low pressure spin seen in satellite animations E of Beryl and west of Bermuda that was getting some attention from bloggers yesterday. This mid-level low is turning eastward toward Bermuda (while steered by the north side of 1023 mb low-level ridging seen in the above charts)..and shows no signs of developing under an unfavorable northwesterly shear environment caused by the upper ridge system in paragraph P2.
P10...Long-lived Caribbean upper ridging persists...and its eastern convergence supports persistent dry air in the eastern half of the Caribbean and waters E of the Lesser Antilles. This upper ridge had an embedded central Caribbean upper trough (as mentioned in discussion #18 paragraph P8)..and divergence E of this upper trough was moistening the air in the western Caribbean 24 hrs ago. Also mentioned in previous discussion # 18 (paragraph P9) was a dissipating tropical wave that had entered the Caribbean...and it appears the remnants of the tropical wave interacted with the divergence E of the central Caribbean upper trough to produce a tremendous increase in T-storms last night...and now we have a new disturbance to watch in the Caribbean Sea. This t-storm mass locally inflamed the Caribbean upper ridging with latent heat release such that the central Caribbean upper trough has split into an upper low vortex over the Yucatan and upper trough SE of Jamaica. 1200Z TAFB has just added a surface trough SW of Jamaica associated with this new disturbance...but the heaviest rains/cloudiness appear to be headed for the Cayman Islands and eventually Cuba. Current prognosis is that if the system wants to develop into a tropical cyclone...the system needs to keep firing t-storm activity to further inflame Caribbean upper ridging...which would reduce southwesterly shear and enhance its outflow.
P11...Tropical wave has been kept essentially stationary (midway between Cape Verde Islands and Lesser Antilles) in the last four days of TAFB analyses. A t-storm mass E of the tropical wave is present along the ITCZ...but the mass will remain sheared-off from the tropical wave by the emerging longwave upper trough regime to its north (discussed in paragraph P8 above). I beleive the formation of this T-storm mass was caused by convergence E of the tropical wave and enhanced poleward upper outflow from the longwave upper trough regime in paragraph P8.
P12...Upper ridge over the E tropical Atlantic continues.