Tomorrow is going to be quite interesting. Biggest challenge is going to be where that sfc low develops and tracks which is going to be heavily influenced by the Ohio Valley/Tennessee Valley convection. I would think the most favorable track for this would be just south of southern New England, but is it across Long Island or just south of Long Island?
In terms of any severe weather potential, this track is key because if the track is across Long Island, the true warm sector and triple point will likely scoot across southern Connecticut, Long Island, Rhode Island, and Cape Cod. There would be potential for some brief tornadoes. If the track is south of Long Island, severe potential is nada (except maybe Nantucket and the Vineyard).
Regardless, I think we're in line for some flash flooding rainfall. upper-level dynamics are pretty strong and we look to be in a very favored position for enhanced upper-level divergence. Looks like H7 warm front pushes well into the region which will aid in lift as well. In addition, we'll have the nose of a strong low-level jet and a very moist airmass.