#1, I get a lot more vigilant about how I’m feeling anytime out in the heat. I’ll back off the intensity and/or shorten intervals. I don’t do too many rides over 3 hrs when it’s this hot, but if I do plan for a longer ride, I leave earlier in the am. I keep an eye on the forecast…the temps tend to be higher in the afternoon, but the humidity is lower (if it doesn’t rain), so a “mostly cloudy” afternoon with a decent breeze may be better than riding in the morning at 90% humidity.
I try to choose routes that have more shade. I keep moving to get the benefit of air moving over my skin (in this FL humidity). I use more ice in bottles and over 2 hours I carry a 3rd bottle with just ice water to squirt on my head and back. I get out in the heat and push acclimating as soon as the temp starts rising in the late spring…it’s easier to hide in the a/c in summer, but it will do you good to spend some time in the heat every day.