No windbreakers needed, maybe just in case, doubt youll use it, especially during the day. Ive done the blue hole, turneffe\lighthouse trip myself 3 times all over night trips. I slept in a t shirt and laid on a sleeping bag out on the dock, dont imagine a windbreaker will be used, but nice to be safe if the wind becomes a factor. The weather is like most tropical destinations, unpredictable. Ive dove in rain before, didnt change a thing. I can tell ya that rain clouds down there blow by so fast you could go in to use a restroom in your apartment and come back out and would have rained, not to say that it cant rain longer, but you get my drift. I would say June and July were the wettest months I ever spent there, and if I recall October was rainy too, but I dont think its a specific schedule when the rains come and go, all do to convection and moisture from the warm ocean. I only spent 8 months down there, but thats what I have come up with. Its a great place, your gonna love it!