I've done five October trips, at different times throughout the month. Weather had varied a lot from trip to trip -- and has even varied greatly throughout the same trip!
I've had: fairly cool for October (low 60s) and very windy; pleasantly warm and not too humid; hot and humid; sweltering hot and humid; and "surface of the sun" hot and humid. One trip, in 2009, it started out in the upper 90s and very humid every day 10 days later, it dropped 30 degrees overnight, and became very windy. I had packed mostly sleeveless shirts and shorts, and wasn't prepared for cool and windy! Had to layer the best I could, but it was tough!
And the rain! I've had trips with little to no rain; trips where we had brief afternoon showers; trips with 2 or three hours of rain per day; and one hurricane!
So it's best to prepare for everything, especially clothing-wise. I now bring long pants, warm socks, jacket, a rain poncho, and even gloves for every trip, even at supposedly hot times of the year! And I always bring my Coleman mini-fan, too. It might seem like "over packing" to some people, but it will save you from having to buy expensive WDW clothing!