That time of the year is VERY hard to predict, and as the other poster said, you never know what it's going to be like from day-to-day.
The best thing to do is bring along the swimsuits and hope for the best.
The pools are all heated, so as long as you don't mind getting out into the cold, you can still swim. They only close the pools when it's thundering, or for another saftey type reason.
Have fun!
Anne