I ran in 75 degree temperature 70 % humidity last night on a little race pace test. I will likely need to slow my best race pace 30 seconds per mile. It's totally bearable for someone acclimated. You just need to take the edge off your effort. Many people treat this as a run party, not a race anyway, so it should be pretty good if we see about 75 or cooler.
Near term forecast for Kissimmee predicts 89, 90, 90 degree highs for Sun., Mon., Tues. That could mean 82-84 degree race start temps. If we see that on Nov. 7, it will present problems for many. It's still way too early to tell. I would bring a cool costume/outfit as a backup. I have a feeling it's going to be hot at race start.
I found a weather site that has predicted Jet Stream and surface winds and temp images:
http://www.weatherstreet.com/states/gfsx-300-forecast.htm