Gman!
We have already been having outside temps of high 80's and 90's (we even reached 100 last month once). When the outside temps get this high, I turn my tub down to 97-98. That is body temp, so I still get some therapy, it is still warm, and I don't get too overheated!
Play around and you will find the temps that feel right to you, at all times of the year! That is how I had to figure out what was right with me! Hmmm...sounds like the process of wet testing!