I think the weather will be perfect for your trip and for the water parks, but please do not take what I say as set in stone, since the weather patterns are crazy this year. It also depends on where you are coming from........I think you will be fine with shorts and tees and perhaps a pair of slacks and a light jacket just in case. As far as the pools they are heated, I haven't been to a water park in a few years but I am sure they are too. I find the Fall in FL to be alot like the summers of up north without the humidity. The best thing to do is check the weather sites before closing up those suitcases. I personally like to pack a light jacket or sweater anyways since I always freeze in the restaurants in the evenings, but that is just me. I think you have chosen a great time to visit, Hurricane season is usually over and the rains of summer have subsided.