I'm born and raised in the SoCal desert. I commute everyday. Summer temps here average 105 and approach 120 occasionally. So yea I know hot, here's what works for me...
A solid jacket that vents well not a mesh jacket. The problem with mesh is that once the ambient temp hits about 95 the air going over your skin starts to heat you up not down. Sounds counter intuitive I know but it's true. Here's a wind chill calculator
, enter 95 deg and 65 mph.
I do wear mesh pants because solid ones get too sweaty, there's not much airflow on my legs. The heat from the motor is greater than the ambient usually anyway.
Once the temp hits the upper 90s I wear an evaporative vest
under the jacket. I have 2 types, a fiber one that lasts about 45 minutes (that I wear for my afternoon commute) and a crystal one for longer rides. The crystal vest is heavy when fully saturated but lasts 4-5 hours.
Another thing is to seal the neck area (so hot air is not blowing in) with some type of lightweight wind fabric. I like a Buff
Rig up a drinking system that will let you drink water as you ride. Take sips of water every 10-15 minutes or so. I partial freeze water bottles and keep them in my tank bag. I have a tube that connects to the bottle and clips onto to my jacket. Having cold water available goes a long way as far as tolerating the heat.
Lastly it takes a mind set that yea it's hot but not unbearable. Riding in the heat is doable for sure maybe not pleasant like a nice spring day but hey you're riding right?
Hope this helps someone...