That's a good question and something I have been watching intently! It's a tough call this many days out. I don't think we will see remnants of Isaac for at least a week. Models are showing between Tuesday and Wednesday at this point, right now! However, at worst, I think we only see about 2-3 inches of rain at max. After Isaac moves inland it is going to move north through the midwest then east into the Ohio Valley. Between the midwest and the Ohio Valley, I think these areas will pretty much get the most of the moisture, which they greatly need.
I will certainly keep an eye on this and more to come as it develops.