Hi Kymma,
I tried replying earlier, but I think it went to the "electronic ether...."
Anyway,
I agree with the other replies: Bring a suit of some type-to avoid stings, etc. You should also consider how much diving you plan to do, and what are you doing when not diving.
For example, last Aug. I was in GC, average water temps in the 82-85 degree range. For the first 2 days, (4 dives a day), a 1 mil. neoprene skin was fine. By the end of the third day, I was a bit chilly. I added a 3 mil vest, 2 lbs,of weight, and all was fine. {I did get an odd look and a "You're layering for 83 degree water?" question, but that was before dive # 15.}
I should add that, in addition to 4 dives a day, I am a devout "shade seeker"on the boat, and elsewhere.
If you are planning 2 dives a day,and the rest of the day "sunning" on the beach, then you might not need the vest.
I'd suggest bringing it-you don't have to wear it, and besides, it is better to be better too warm, and let some "cooler" water into the suit, than too cold.
Whatever you decide, I hope you enjoy your trip.
Good luck,
Mike