Okay....I've been to WDW in August more than once. The reason I won't be going back at this time???? The extreme heat/humidity. You notice I say nothing about rain. We had one stay in mid-August that we prayed for rain, every day. But it never happened. It was brutal.
We have been there with a hurricane...Charley passed right overhead on that stay.
It rains in Orlando almost every day during the summer. When it does, it feels so much better afterwards. With that in mind....every day, when you are packing up to leave the resort for the parks, put a disposable poncho for each person in your daypacks. That way, if the skies do open up, you're good to go. The one time I didn't do that, it poured. Poured and stormed badly enough to shut the monorail line at MK down for almost an hour!!! The sky was beautiful when we left the Polynesian, by the time we got to MK, the storm was over us and the monorail stopped dead in it's tracks. Hundreds of guests stayed on that platform, waiting for the storm to pass. Finally, after about 40 mins, some of us got tired of waiting and dashed for it. It was so dark, at 3pm, that the lights came on in MK!!! Oh, man...that rain was incredible. But it sure did clear out the park!!! And of course, that was the day we had no ponchos with us. So, pack them...everyday.