The vigorous tropical wave that left Africa days ago is now sharpening and becoming more convectively active as it enters the western Atlantic. The signal on guidance has favored tropical cyclone genesis for days now--much closer to the U.S., and the NHC now designates the area as having 60% odds of development in the next week.
Originally, the sprawling wave traversed the eastern and central Atlantic devoid of convection due to the presence of strong SAL. While this prevented convection from developing, a combination of low level moisture pooling, high SSTs/OHC, light wind shear, and diminishing influence of SAL has allowed for gradual disorganized convective development, the first step toward TC genesis that's most likely days from now.
https://tropic.ssec.wisc.edu/real-time/mtpw2/product.php?color_type=tpw_nrl_colors&prod=natl×pan=120hrs&anim=html5
The large wave is now draped across the Greater Antilles, and there are numerous questions over the evolution of the wave in the next 5-7 days. First, how does the wave interaction with the Antilles spur or tighten vorticity? The GFS tried to spawn more robust vorticity after interacting with Haiti/DR, while the Euro for the most part has focused an eventual vortex in the convection that is north of the islands. This obviously has track implications.
Second, how does a developing wave take advantage of what is likely to be a favorable upper level environment closer to the US? Does it develop faster, as the Euro until today suggested, and get pulled northward and then kicked OTS or NE by a developing Midwest trough, or, if things are delayed and track into the Gulf as the GFS suggests, where does it go?
Third, what will be the steering pattern? There's an increasing signal that the steering pattern between an Atlantic ridge and Midwest trough breaks down as the disturbance reaches the east coast or Gulf, creating immense uncertainty on both track and intensity forecasts.
The bottom line is that there's a lot of uncertainty with the forecast ahead. Ensembles are the way to go as we move forward the next few days to get a sense of the envelope of possibilities--which are very broad as it stands. OTS to a Gulf threat are on the table. The Gulf and SE US should watch this closely.