If you are going to Disney World, it will rain. It doesn’t matter what time of year you go, it will rain. Most of the time these showers are heavy, but only last for a few minutes (unless you hit a real storm like we did once where it rained for 4 hours straight, no joke). The best thing you can do when it rains is put a poncho on, and go about your day.
I prefer a heavy duty reusable one that I can use over and over, but disposable ponchos will work too.