2012 Atlantic Hurricane Season Birdseye Discussion #42A (Special Update)
...JULY 4 2012...3:25 PM EDT...
Two areas of interest have quickly popped up on this 4th of July. One is located over the Lesser Antilles...Virgin Islands...Puerto Rico...and eastern Caribbean Sea...associated with the tropical wave in full discussion #42 paragraph P11. The second is located offshore of the northeastern United States...associated with southern Hudson Bay frontal cyclone mentioned in paragraph P1 of full discussion #42. Both pop up areas of interest and their surrounding environment are shown in Figure 1.
Figure 1: Two pop-up areas of interest this afternoon and their surrounding environment. Paragraph numbers are associated with full discussion #42.
Cocerning the eastern Caribbean tropical wave (full discussion #42...paragraph P11)...the National Hurricane Center introduced it into their tropical weather outlook this afternoon because of gusty winds measured over the Virgin Islands. This re-enforces the vigor of the tropical wave...but the National Hurricane Center gives it a 0% chance of developing in the next 48 hours. While it is currently under a favorable east Caribbean upper ridge (paragraph P9...discussion #42) that is enhancing its upper outflow...the tropical wave is not producing enough storm activity & associated latent heat release to expand the size of this upper ridge. Therefore...I too still expect no development with this tropical wave as it encounters unfavorable westerly vertical shear associated with central Caribbean upper vorticity (as shown in Figure 1 above).
Concerning the quickly growing cluster of thunderstorms offshore of the northeastern United States...this is associated with the warm front of the southern Hudson Bay frontal cyclone mentioned in paragraph P1 of discussion #42. This area of disturbed weather should move east away from land while located amongst westerly flow on the north side of the open Atlantic ridge (paragraph P5...discussion #42). Because warm air advection ahead of the Hudson Bay frontal cyclone has amplified central North American upper ridging over the warm front and disturbed weather (as shown in Figure 1)...I believe this has a better chance of developing than the eastern Caribbean tropical wave...especially if the upper ridge axis stays aligned with the disturbed weather such that it continues to enhance its upper outflow similar to a tropical cyclone. Water temps over the south half of the disturbance are at or above 26 deg C...sufficiently warm for tropical development. Meanwhile...the Tennessee Valley cut-off upper low and surface trough it is supporting...also left behind by this Hudson Bay frontal cyclone...shows only widely scattered t-storms across the SE United States on radar.
Return to full discussion #42 for current situation across the rest of the Atlantic tropics.