Tropical weather analysis - June 14, 2010

Invest 92L, much to my surprise, did not become a tropical depression this morning. It appears that a burst of southerly shear impinged upon the system this morning, significantly disrupting its previously impressive organization. Estimated center position based on the last of the visible satellite animation loops is 11N 42W. Clearly, this system has gained considerable latitude since this time yesterday, when it was still at 7 to 8N. This gain of latitude is important, because the further away from the equator a storm is, the greater amount of spin is available thanks to the Coriolis Force. This in turn allows a better chance for tropical cyclogenesis, since, obviously, tropical cyclones contain a lot of cyclonic vorticity. The system is currently moving WNW, based on various satellite animations.

Also, the southern half of the circulation is slightly exposed south of the deep convection, which is elongated S to N and not well-organized. Analysis of water vapor animations as well as University of Wisconsin CIMSS wind shear data indicates that 92L is experiencing about 20 kt of southwesterly vertical shear on its western side. The catalyst for this shear is a large and persistent TUTT (Tropical Upper Tropospheric Trough) located across the central Caribbean.

However, this shear has not penetrated the core just yet, as evidenced by the greater convective organization there. Overall, low- to mid-level vorticity has become better organized today, though it is still not perfectly aligned in the vertical. As per CIMSS analysis, upper-level divergence and low-level convergence have remained constant throughout the day, with the latter actually slightly increasing over the last three hours. This will support continued convective development, since dry air not an issue.

However, I think the models are grossly overestimating the magnitude of the current shear, and I am not expecting 92L to become a tropical depression, at least in the near-term. At most, it has a 24 hour opportunity with which to intensify before shear gets even stronger. And even that estimate seems a little generous based on what I see.

However, beginning in around 72 hours, models unanimously predict a substantial relaxation of the TUTT. By this time, 92L should be nearing the Leeward Islands. Assuming its structure isn't too disrupted by the current hostile environment, it may have a greater shot (relative to this morning) at becoming a tropical depression during this time, and beyond. I am expecting a continued WNW movement throughout the period, albeit with brief oscillations to the north and south. Smoothing out all of the wobbles leads me to a mean WNW motion toward the central Leeward Islands in about four days.

Regardless of development, locally heavy rainfall and strong gusty winds are a strong likelihood across the Leeward Islands and Puerto Rico in about four to five days, and residents in those locations should carefully monitor the progress of this system.

Elsewhere

Elsewhere, as per 1200 UTC analysis from the National Hurricane Center, a tropical wave is noted from 2N to 12N 25W, moving W. This wave has been generating persistent deep convection for nearly 24 hours, and certainly bears watching. Upper-level winds appear rather conducive for development of this system over the next several days. A general W movement should continue with this system over the next several days. This system might be the one to watch, not 92L.