The temperatures in October can vary. I have been there and it was hot and humid and then in the same week had to wear long sleeves at night. It also depends on what time in October you go - earlier or later! I would prepare for hot but have a jacket if temps get cool at night. As for the rain, one year we didn't have any rain then the next it rained every day! I know this is not a lot of help but the moral of the story is it is unpredictable and just be prepared.
Also a rainy day at Disney is better than a sunny day at work/home!!! Have a great trip.