FLHurricane.com: TD 20 Forms in the Caribbean, TD 19 Out at Sea

System NW Caribbean: What's interesting in watching this area of disturbed weather over the last couple of days is that it keeps generating these llv vorticity maxims that summarily decay. I've seen 3 so far do this, where/when a tightly clustered region of cold cloud tops amid the greater area of convection decay, and in their wake there is a "tendency" in visible imagery for llv cloud rotation. These that I have witnessed have been on the order of a mere 50 nautical miles in diameter (est) and do not persist for too long before decaying them selves.... At which point, there is already another cluster of intense convection developing in a separate area, and the cycle seems to repeat. It really does appear that this region of the W and NW Caribbean is creating weak tropical lows as a response to convection "not quite" persisting in the same location long enough to make use of the time-dependency and corriolis forcing with air that is moving inward toward the upward moving air of these thunderstorm clusters. Moreover, if you look at the cirrus blow-off from Yucatan thunderstorms you note that they are moving E or ESE pretty clearly...This tells me that there is shear in the environment.. Not sure but do suspect this is partly why any given thunderstorm cluster isn't persisting, because the mechanics in the U/A are not quite right for difluent motion at this time... As HPC is pointing out however, these U/A conditions are expected to be more favorable sooner rather than later so it may just take off like all at once, once these U/A winds come around to a better anticyclonic impression.

We'll, see..

System S of Louisiana and near the mouth of the Mississippi: Frankly and surprisingly it appears like it has a better llv vis sat presentation than 99L. The upper U/A is a bit hostile however. What is interesting to me is that if this feature can persist beneath the mean steering field it would like avail of better U/A later on... Interesting prospect when you consider that we are likely better than 50% that a system will finally wrap up near 99L and the proximity of the two systems are close. If the system in the Gulf never does get deeper in the troposphere that is, it would likely just be asorbed in the circulation field of 99L.

System of the SE US Coast: That event (if occurs) is interesting... At first glance of the global based model I'm inclined to think it is primarily driven to existence by numerical instability of have a strong anticyclone moving off the NE US Coast, which in turn imparts a long fetch of modifying continental polar air over the still very warm Atlantic waters. This enhances baroclinicity in that region as a natural conclusion. Essentially, this configuration of having a trough developing in the Nations heart land, balanced against a anticyclone near 60W/45N (appr loc) teleconnects nicely to a weakness along the SE US Coast, and combined with said temperature gradients N/S in the west Atlantic Basic is actually quite often a precurser forecasters look for prior to Nor'easter/coastal cyclogenesis in the winter... Therefore, it is difficult to be totally certain that whatever forms there (if anything) wouldn't be more of a hybrid type subtropical low... In either event, there should certainly be an inverted trough in that location. Should the apparent developing gyre near 58W/21N assume a true warm core and attending structure, that would confuse this, because it is likely in my mind that an inverted trough/subtropical low could form off the SE US Coast without this feature currently moving WSW through said lat/lon. You could actually end up with an inverted trough that has a true tropical system approaching its lower axis from the ESE.

Definitely lots to consider!

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