As a general rule on the coast, May June and July have higher temperature then it will sag in August, September and 1st two weeks in October but the humidity spikes. Hottest day I have experienced in Mulege was 100.6 F with a humidity of 78% it was unbearable. A decade or so ago a gringo group sat at an outdoor patio and had a late dinner in July. Around 10:00 PM, the wind increased to about 50mph, the temperature was near a hundred degrees.
When I arrived in Laughlin Nevada at 12:01AM in 2010, the temperature was 101F. Could not walk within 20 feet of the concrete hotel casino. The concrete wall was radiating heat like a blast furnace. When I had passed through Lukeville, the CBP dial thermometers were reading 122F
I tried to go to the library in Ajo NV. Found a sign on the front door -- TOO HOT WENT HOME!
I learned the hard way to carry a bundle of cheesecloth and 5 gallons of water when it's dangerously hot but arid. Soak the cheesecloth in water then drape it around you. Beware of yellowjackets.