We always go in August and yes it is hot and humid! First thing I plan on is that it is going to be that way and prepare for it! Don't wear anything heavy! Never wear jeans there! I bring board shorts and other clothes made of microfiber. They are light weight and dry quickly.
Drink lots of water, but not the water out of the drinking fountains and tap! Yuck! I bought some Britta water bottles off ebay. Money well spent! They have their own little filter. We fill them with mostly ice to start with and can even drink out of the drinking fountains with them!
Next, sunscreen!, sunscreen!, sunscreen! Never leave home without it! LOL!
We will be there around Aug. 15th for about a week. Then we are supposed to go to the Keys for about 5 days and then will be coming back to Disney for the remainder of our trip. I am booked at SSR for the first part of our trip and BCV for the last part.