Splashmom, I completely understand your concern about the heat. Were we live we are use to the heat, but not the humidity. We have never gone in August, but late September was pretty intense last year. This is what we did:
Be sure to wear a hat and sunglasses and use suncreen.
We purchaes the insullated water bottle holders, which have a zipper closer and a strap to make it easier to carry. We put the water bottle in the very top of the room frig and it would get a bit frozen. We also would add ice water from any CS place. They will give you a cup of water at no charge. So we would order an item and water.
Go early in the day then head back to the resort for a swim, nap or just enjoy the resort. We love Animal Kingdom Lodge because there is so much to see without going outside in the heat.

We would then head back to the parks in the late afternoon for a sit-down dinner then enjoy the cooler evening hours.
Another idea was to head to one of the large Epcot areas inside. One of our favoites is The Living Seas or Innoventions. We save those for either the heat or rain.
My DH has a health issue that requires him to not get over-heated, so we purchases one of the neck wraps which you soak in cold water then place around your neck. That with a hat and sunglasses really helped him. Also, look for shade whenever possible while wating.
If you plan your days it really isn't that bad. Just remember to take breaks and if you get over-heated go into an air conditioned area or at least shade. Remember to keep hydrated and that means water or a sports drink. You are going to LOVE AKL
Angel