We have had 4 trips during the 3rd week of Oct.
It is usually mid 80's, but still feels hot due to the humidity. One year we had record breaking heat- had temps in upper 90's the whole week. We would walk out the door in the am, and the temp would already be 86! We kind of melted that week, but still had a great time, just drank a lot of water!
It is still pretty crowded at that time, but we rode all rides multiple, multiple times with Legacy FP. AM EMH was awesome, we could do all of fantasyland in first hour.