Heat is something your body can acclimate to fairly easily.

[war story] When I hit the ground in Saudi Arabia in 1990, it was 104 F at 2 a.m.. We saw temps as high as 135 F, and we were wearing chem gear over BDU uniforms. That's like wearing a quilt. It was damn hot. It took water, and very little time, to be able to function in this heat for 12 hour shifts. [/war story]

The key is hydration, nutrition, and acclimation. Ride year round or at least start early as it starts to warm, and at least a little daily. Your body will be ready as it gets hotter. Same thing in the fall. Done gradually, the human body can adapt to an incredible range.

And this is coming from someone that's not happy if it's about 75 F.