Just got back. It's all relative. We are from NH but we travel in the tropics every summer and can deal with humidity and heat. For the most part, the temps this past week were from the high eighties to low nineties.
The temp wasn't the killer- it's more the humidity. Also, the shade was so much cooler than the sun. I can't stress this enough- if you're out of the sun you should be fine. I never got burned and never used sunscreen this whole trip. However, do bring sunscreen!
You'll have a great time. It did thunder and stuff but most of the time it was a false alarm. For the week that we were there, there were occassional passing showers but nothing lasted longer than 15 min. At night, there was heat lightning sometimes. It added special effects to Illuminations! I saw people carrying around ponchos- what a waste. If you just duck into an indoor attraction or shop you should be fine within a few minutes.
The first day we arrived, there was a huge thunder storm. Every precipitation seemed to be in the afternoon around 3pm. Luckily at this time we were in our resort relaxing so we never had to worry about being caught in the park.
Check accuweather.com -It's a good site. Don't be wary about 30-40% chances of precipitation. Be more wary over 50%. We had the pics of thunderstorms the whole week we were there and everything was fine.