It is Summer here in Portugal and while I don't live in the warmer midlands, the coastal regions get quite hot too. It was 95-105 F on my ride mid-day on Thursday. That was my limit since it was tough to train properly. Just cycling like a tourist, no problem, but to train I prefer cooler. The wind was like a hot blow-dryer!
Generally I ride at 6h30 now so that I am home before noon.