It is full summer weather that last week of May. The humidity is still down (compared to July and August), but the temps are in the upper 80s and 90s. For some reason, the weather seems to really heat up in May. At the beginning it is usually 70-80 and by the end of the month, in the 80s and 90s.
Now, I don't live in Florida, so maybe someone else has a better perspective, but that has been my experience. May (other than Memorial Day weekend) is my favorite time to go. Unfortunately, with two older kids, missing school is just not an option anymore.