Been there the 3rd -- 4th week in Sept three times in the last 10 years. I consider it hot and humid (not like August, though). About 90 degrees, and be prepared for showers ---- usually brief, but a few torential downpours for a short time. Crowds were low the years we went, which is a big advantage. It's a great time to go, but I still have to pace myself in the heat.