A stream of deep tropical moisture remains over the area through which impulses of very heavy rain are moving. Additional torrential showers and thunderstorms are expected in parts of the area through the afternoon, exacerbating the flooding situation. It does look like the setup changes a bit after that and we will no longer have that convergent focusing mechanism. Nevertheless it looks like there will still be a few showers and thunderstorms around Friday and Saturday and there is at least a chance of one on Sunday.
The rain that occurred yesterday (and especially last night) was heavy enough to cause flash flooding, and we aren’t totally done with rain just yet. There was close to 4 inches at BWI, but some spotter reports indicated greater than 6 inches in some neighborhoods.
There are a series of “plumes” of rich, tropical moisture that are helping to feed these heavy rain showers and thunderstorms. One of them early this morning is causing flooding just east of Philadelphia, and it is extending all the way up into central New England. Some of those places (like in Vermont) that experienced massive flooding when Irene moved through are again being threatened by serious flooding.
Katia will be spreading heavy wave action along the East Coast, and there are already some advisories out for high surf and strong rip currents. These will probably be in effect for the next couple of days, and this whole miserable pattern doesn’t look like it’ll completely unravel until some time later this weekend or early next week. As we had discussed yesterday, there’s no mechanism located upstream that will be able to “boot” all of this rich, tropical moisture.