I've been lots of times in October and am about to go again later this month. I feel you on the uncertainty!
There's a huge chance the weather will be lovely, with highs in the 80's. But one year (2008, in fact) a weird cold front came through on October 28. We were totally unprepared and had packed only shorts and short-sleeved tops! It became jeans and long-sleeved top weather overnight . . . I want to say maybe highs in the upper 50's or so. Deep in our Disney cocoon, we hadn't heard a weather forecast and foolishly left for the parks in our shorts; we rapidly became miserable and were forced to buy jackets.
Now I pack mostly shorts and t-shirts, but throw in a few pairs of jeans and a light/medium weight jacket as well.