Ugh! It’s not just hot, but humid too. Humidity hurts because it hinders your body’s natural ability to cool itself. The air has more moisture in it so the moisture from your body (sweat) really has no where to go except into your shorts, socks and shoes. In the Midwest, it can get particularly nasty for extended periods of time during the summer months.
While you can still run in hot humid conditions, you are wise, at least when the muggies first start, to slow your pace down. Your heart will have to work harder to keep your body cool which means that you are actually getting a decent workout even though your paces have slowed. Revise your training and racing expectations and have fun with it. Be sure to drink plenty of fluids and get electrolytes. I prefer taking Elete tablets than dosing with Gatorade or other “sports drinks”. Mostly that’s because of my food allergies. I take at least one tablet a day in the summer and when I’m doing long runs in the summer, I may take 2-3 during the run itself and carrying water with me. Sure I sweat a ton and it gets uncomfortable and I’m constantly doing laundry, but I figure I’ll be in awesome shape come fall!