I don't want to give you the wrong impression that it's astronomically hot. It's probably cooler than if you came to visit central SC in August. Here are a couple sites about the trends for GC:
http://www.caymanactivityguide.com/Weather.htm
http://www.frommers.com/destinations...177020006.html

I find that Frommers typically has pretty good "When to Visit" summaries in their guides.