Hi squeekymouse, welcome to the DIS!
You will discover that it is VERY hot and humid in Florida during the month of August. Often there will be an afternoon shower as well. The great thing about being at WDW is that it's easy to duck into an air-conditioned building quickly if you need to get out of the heat. We just visited Cedar Point last week and I was amazed at how difficult it was to find air-conditioned buildings, especially restrooms! At WDW all the shops, pavillions, inside rides, restaurants, etc are nicely air-conditioned.
When we visit WDW during the summer months we always get up early and head to the parks as soon as possible. If you arrive at opening you can enjoy a couple of hours with a little more comfortable weather and lighter crowds. We then plan a nice sit down lunch somewhere and head back to the hotel for swimming/rest and relaxation. All refreshed we'll head back to the parks in the evening and hope that it has cooled off a little bit so that we can enjoy the evening entertainment.
Be sure to bring plenty of sunscreen and plan on taking it slow. Have a great trip!