This link is from the Weather Channel and shows average highs, lows, and rainfall for each month in Orlando. It shows ON AVERAGE that September is still wet. But your experience will vary.
Also, it's big-time hurricane season - most of the hurricanes seem to hit the gulf coast in September - If you are putting out lots of "$$$$" for your trip, would include trip insurance. And yes, September can be very hot still, if that is an issue with you. Of course, always exceptions! As you can see from the chart, the averages for April - Oct. don't vary a whole lot. I can attest to that being from near the gulf coast.