Hot and it can be very WET as well. I swore off September visits for a while after our trip in Sept. '02. We stayed for 6 days and had at least a half-day of rain (started mid-afternoon and ran well into the night) 4 of the 6 days.
One of the people in our party had golf outings planned 3 days, and only went once due to unplayable conditions. I'm not sure that he even finished the round.
Other people will tell you that they had great, dry weather that time of year. Just be aware that it is one of the riskier times to visit, IMO. It does fall well within hurricane season, so you can never tell what sort of storm front might move in from the gulf.