August is hurricane/tropical storm season, although in the Western Caribbean storms are much more likely September through early November.
I've enjoyed quite a few early Augusts on Ambergris, and the weather generally has been pretty good -- quite warm and humid, but not a lot of rain. Of course it's impossible to predict the weather for any particular period, and this year seems more unusual than most in the Western Caribbean and Gulf, with heavy rains from early tropical storms, so anything could happen.
--Lan Sluder