Hi
The weather should still be very nice in September, or least I hop so because I am going back next week!
I went in May, and was told not to expect hot weather as it was very early on in May and is the ealy season. But in fact there was only two thunder storms (at night) and the rest of the time the weather was in the 90's!
It was loverly if all you want to do is laze on the beach. I should imagine that the temperature average for that time of year is still in the eighties, as currently its around 88!
Have a great time!
Kate