Hi Dave – I’d expect water temp to be around 80F-82F, so the thermal requirement would be pretty personal. Very possible to go with no wetsuit.
Despite that, I would recommend something that gives you more protection than a shortie. Maybe a diveskin or a light weight fullsuit. Don’t buy anything, just think about it and maybe rent something to try out.
When my wife & I started diving, it was mostly warm weather vacations including the Caymans. We rented all equipment apart from mask & fins, usually including shortie wetsuits. We eventually bought our own 3ml fullsuits, mostly because even when you’re careful, you can inadvertently touch stuff that burns or cuts and it’s nice to be protected. There is sand with fire coral debris in it, stinging soft corals, and if you are in a wreck, lots of sharp edges. Also tripping and falling in difficult shore entries & exits.
We also discovered that even though we’re used to Canadian lakes & 65deg beaches, after we’d been in 80 degree plus water for an extended amount of time without any neoprene 3,4 5 times a day, it got cool. I can’t say that on some specific warm water dive, I absolutely needed a fullsuit, rather than a shortie for warmth but I’ve always been comfortable and never felt overheated in a 3ml. That’s just me.
It’s great that you are asking “what should I try” rather than “what should I buy”. Try different stuff before you decide to buy anything.
And have a super time in GC !
BillF