We are leaving Sept 1...hoping for a good weather trip...we have a fireworks cruise booked during the trip...hoping for clear skies.
Back in my very early teens I went to WDW during a tropical depression that seemed to sit over the Orlando area, the whole time we were on vacation. We never saw the sun...the rides were up and the parks were dead...I have a distinct memory of riding space mountain over and over, just running around the building and through the lines and walking right in.
I did get athlete's foot for the first time ever in my life, because of constantly wet feet..THAT was very uncomfortable...if you have a overly rainy trip, I'd suggest (based on my experiences) water proofing sneakers and lots of pairs of socks or shoes that dry very quickly, or 2-3 pairs of shoes...wet socks are icky! lol!
Besides that I'd go to the parks like normal. I would not worry about a poncho if it is going to be constant rain with high humidity, because ponchos just make me feel hot, sweaty and trap way too much humidity. Either way, you are going to be wet. I'd prefer the rain....sweaty drowned rat or just drowned rat...your choice! LOL!
oh.. and avoid wearing denim shorts. They turn into heavy wet denim never-seeming-to-dry shorts...Let's just say "avoid the chafe".