It's been a few years since we were there in May, but it seems like a perfect time to go. The weather was warm (not quite hot enough for a native North Carolinian who loves the heat AND the humidity

) enough to need the water parks/rides, but the nights were very comfortable.
I completely agree. We went at the end of May a couple of years ago and it was perfect. Crowds were low, there were only a couple of rides we did the fast pass on.
Hey UNCCLaw, we are from Raleigh as well and are going in Sept time frame.
Have fun.