Walt Disney World is in Florida and according to Google, it is 'humid subtropical', a fancy way of saying, hot, humid and rainy. I have had vacations at WDW with nary a drop of rain and then there have been vacations where there was a rainy period every day.
In May of 2014, it was hot and humid the whole time I was there. On my last day at the Magic Kingdom there was a little bit of relief, it rained!
I was near Space Mountain when it started and I decided I wasn't going to get my rain poncho out, I went in the store at the end of Space Mountain and found not only a place to sit but I had free entertainment when a group of teenagers decided to wait out the rain by charging their phones.
When the rain stopped I got right back outside to enjoy those few minutes when it feels cooler before the sun comes out again and steams up the rain water and raises the humidity again!
Afternoon rain showers are common at WDW, you can be prepared with a plastic rain poncho and just keep going, often the ride line-ups thin out when it rains. Or you can duck into a store and do some shopping. I have heard a lot of people complain that rain just ruins their vacation . . . it doesn't have to, have a rain strategy and the magic never has to stop!
If you want a great idea of what to do with your Disney Poncho when you get home, check out this article, also by Gaylin.-Nick