Invest in a cooling vest. I have one and have worn it many times when riding in the desert with the temps over 100 degrees and have felt very comfortable.
The only drawback is that it is a wet vest so keep your wallet someplace dry.
It acts like a swamp cooler with the wind blowing through it keeping you cool. When you are stopped, that's a different story.
They're well worth the money spent on it for keeping your core temps down and preventing heat exhaustion or heat stroke !