I did my first century yesterday up in IL/WI and the heat about killed me. I'm very heat intolerant to begin with, and it was around 100 degrees (humid, too) with no shade where we were riding. I bonked around mile 80 and had to be pulled the rest of the way by my partners, but the bad stuff came later. After the ride, I was lightheaded, barfing and felt hotter than I've ever been. Couldn't concentrate on anything and thought I might croak. I kept rubbing ice all over myself and hung out in the air conditioning. Drank a lot of ice water, went to bed early, and didn't start to feel like a human until around 2am.
I'm glad I got a century, but I think if you're heat intolerant you should watch yourself. I really should have SAGged out of the ride.
Bring on Autumn, please!!!