We went in August last year (sounds such a long time ago now

).
Are you staying on-site?
August is very hot and humid, and last year it was very wet too. The usual climate is high heat and humidity; which triggers afternoon thunderstorms, which are over in an hour or two (last year they seemed to stick around all afternoon and evening!).
The beginning of August is busy, although crowds fall off towards the end of August due to a lot of schools going back in some US states. We stayed on-site and didn't find the crowds that bad as longas you get to the parks early, (we skipped breakfast and had an early lunch), and then go back to your hotel in the hottest part of the day for a swim or siesta. Then return to the parks later in the day/evening.
Take plenty of water with you, the heat and humidity is really sapping. You can use the water fountains, but I find the water tastes yucky!
Opening hours tend to be long in the summer, so you can spread your park touring and not burn yourselves out.
We made PSs for most of our sitdown type meals and I think in general it's recommended, unless you eat at less busy times. We got a seat in the restaurant in Morrocco without a PS in the early evening without having to wait.
The more popular dining locations do get booked up very quickley though.
We found eating lunch early was good - from 11-11:30 most of the counter service places were empty
