I grew up in FL. That is the typical forecast for the month of August. You will probably get a quick thunderstorm every afternoon between 3 and 5. You will have a great time!!!
We were there the 3rd week in September last year. Forecast was 92-93 with t-storms everyday. We saw some nasty looking clouds but the only time we experienced actual rain was for about 10-15 while we were on the bus back to the resort for an afternoon break. The temperature forecast was correct.
We just got back today.
And that pretty much describes our weather but it honestly was fine. Definitely either take a poncho with you or just be prepared to buy one if you need one. Most of the time the rain was so short that we could easily get inside to wait it out. Sometimes we would be inside an attraction when it happened and it had stopped when we got out, but we knew it rained because everything was wet. A few times we did need ponchos but we just kept on going.
There were a couple of times when thunderstorms did interfere with our plans- like when the Dream castle show ended suddenly only halfway through due to lightening, or when LMA was delayed 20 minutes (and the stands were packed already) but really those were the times you just had to go with the flow.
The plentiful clouds and frequent rain did actually help to cool the air much of the week, I thought.
Please don't worry, have fun! Wish I was still on the "before" side of my trip!