Very hot and humid, and often rainy (it's hurricane season!). That said, we always go during this timeframe due to the Food and Wine Festival!
I use a mini-mister-fan (found it at Walmart) which I love. This next trip, I'm also going to bring a bandana to put around my neck (wet), and some ice in a ziploc bag. Take indoor breaks whenever possible (go into the shops, into a restaurant, or into an indoor attraction to cool off).
I find that if I go back to my hotel mid-day, take a quick shower, and change my clothes, it's very refreshing (I hate sweaty clothes!). If you have the time, you can also take a quick dip at the pool mid-afternoon to cool off.
Drink tons of water - it's very easy to get dehydrated before you realize it.