The operative words are "isolated", "chance" "maybe" perhaps" ,"localized" etc etc. Meaning they really don't know if or when or even where it may (or may not) rain.
Our experience in going to WDW this time of year (since 1975) is that IF it rains, it's usually later in the afternoon, and for about an hour or so. Then it drys up, the sun comes out, and you don't even know it did rain!!