It was by far the hottest, most humid day we've had this summer. Friends who have ridden far more difficult rides recently, in terms of terrain, felt that it was the hardest thing they had done in a long time.

I think moisture (perspiration and rain) were probably the real culprits. One issue could be that your shorts/chamois are not good for hot weather. I have some shorts that feel very clammy on hot days compared to others. Also you might find that powder like Anti-Monkey Butt would be helpful.

For rain, the best thing is a rear fender to keep spray off your back, and a good jacket that covers your butt. I did not have my fenders on Saturday and my shorts were far more soaked by the rain than they would have been with a fender.