Their peak season is between February and May. June will see a decrease in rates, and a corresponding increase in temperature and humidity

While I've never been in August (the natives swear its unbearable), I have stayed in June...and I much prefer the extra heat and humidity to the throngs of people present in March/April.

I'd be weary about a vacation down there between July and September though due to hurricane season being at its peak. It's probably a 1/1000 chance, but still something to consider.

Hope this helps!

Matt