I've never needed bug spray in October, and that is the only time of year I go. We didn't need a jacket, either. It was nice at night, and 80's during the days. We swam every night around 11, and the only problem we had was being a little chilly when we were wet after swimming & walking back to the room.
I've gone twice in the past 3 years during October, and had rain maybe 10 minutes out of 13 days total. But be prepared for anything. It can get hot, it can get chilly, it can be dry, and there can be a hurricane!!!!
Robyn