Yeah, it's funny because last night they were predicting a low chance of development. However Bertha is moving on-shore at Charleston which is helpful.
I've read up on the abort scenarios (and posted an article above) but there seems to be some black magic in determining how many and which of the abort locations have to have acceptable weather for launch. NASA hasn't actually posted a solid number, but I'm assuming that is due to making some compromise decisions on which sites are acceptable.
And just because these things happen, in an article about the DoD teams that support abort landing, we have this tidbit:
Oops! It's going to be a nasty day to be launching aircraft from CharlestonAny other Atlantic splashdown would fall to Rescue 2 from Charleston [South Carolina] because they have more powerful aircraft that could reach Starliner or Dragon or Orion quicker than the Patrick [Florida] support craft.