There is always a chance of rain in Orlando! Chances are, you will just get a brief shower and you can just head to a shop, restaurant, or indoor ride while it passes.
On our last trip, late one afternoon while we were at EP, it started to rain. We'd left our ponchos in the hotel so quickly bought some and tried still doing World Showcase. We were drenched despite the ponchos and miserable, and since it didn't look like the rain was a passing shower, we headed to our resort instead. But that was a heavy, steady rain that is more unusual for the area.