B/4 our trip it said 60% chance of rain for 4 of the days we were going to be there. It only rained for two and for only about 15 minutes each. It was heavy rain but we had a stroller cover which kept everything dry, including our kids!!
www.wftv.com is a great local station. When it is hot and humid we do get afternoon rains. They are widely scattered so one part of the park may get rain and not the other. Just bring your poncho and you will be fine.