Personally, I think this scenario is a classic "slow fuse" development. Most Caribbean August "messes" start as an interaction between a sfc trough, weak upper low, and mid-level energy. First, instability supports divergence-induced convective activity and thunderstorms, but low-level shear is too strong. Later, the upper low fills and moves westward, and it leaves a piece of sfc trough-induced "energy" over the Caribbean Sea. You slowly begin to observe decreasing shear, intermittent convective bursts (but nothing immediately sustained), and increasing low to mid-level vorticity. It takes time for a sfc low formation, but you eventually witness development. Once you get a defined low-level circulation under these increasingly favorable conditions, you can see quick development to a TD, TS, or hurricane (homegrown cyclogenesis). Convective activity sustains itself during the day, and we have an imminent developing tropical system.
I would not write this system away - as I mentioned in a previous post, all ingredients for development are there; look at the weak low-level inflow on most sides of the system. That's a sign of a weak building anticyclone. Actually, it looks more interesting than earlier today -
look at this shortwave loop. Note the increasingly "consolidated" appearance of the convection near 16N and 79W. Low-level convergence is very well established across the central Caribbean Sea, so the "fuel" (including instability) for convective thunderstorms has been initiated. The upper low is moving westward across the Florida Keys, so the energy will remain in place across the central Caribbean basin. Additionally, low to mid-level shear is relaxing per obs. I think the stage is set for the beginning stages of cyclogenesis. Upper-level support is becoming more conducive for the establishment of a sfc low (possibly low-level circulation because of the excellent low-level conditions).
Latest shear charts:
http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.htmlI think we will soon see our next INVEST within the next few days.