Have lived in Tucson, AZ for 33+ years. Now retired, but commuted to work year-round for over 16 years every day.
Warmest I've commuted in: 117 degrees, 2% humidity.
Wet cycling cap, wet bandana around neck, one bottle of cold water and pedal home.
Have also done a century on our tandem in Maryland in summer: 98 degrees, with 98% humidity.
Neither rides were not fun, but do-able . . . Hard to find a shade tree in the desert . . . if you're lucky a telephone pole or saguaro cactus could give you a brief respite.
We've got distances here with 50 miles of no shade, no convenience stores, no people; a-h-h-h-h but we've got sunshine year 'round!
Pedal on!
Rudy/zonatandem