This year will be the third year that I've been to Orlando in September - the weather is superb, nice hot days with a cooling downpour part way through the day - which due to the heat virtually disappears almost instantly. Arriving early at the parks mean you can do all the big rides with virtually no queues leaving you to explore the parks when it gets busier later on through the day - this to me is the biggest advantage of going in September, superb though the rides are, I wouldn't necessarily want to spend a huge chunk of my holiday queueing for them.
As regards hurricanes, we caught hurricane Jeanne last year, it meant we had one day confined in the hotel which wasn't particularly a big deal, and seeing the hurricane was certainly an experience! We're going for three weeks this year and I wouldn't be surprised if another hurricane hit, but they are certainly prepared for them over there and they respond magnificently, so selfish as it may sound, it doesn't affect your holiday too much.