NY, I have had the same experience with humidity. It's the same thing early in the morning, when I ride. The temperature is coolish, but the humidity makes it feel warm. It's the only reason I have ever arrived at work sweaty, when commuting, too.
We are experiencing early September like temperatures and rising humidity. I hate this. And we are getting that rain, too, on Monday and Tuesday.
I rested today. I have my bootcamp tomorrow; debating whether to ride there as my warm up, or ride to work, or both (or neither). Riding 2.3 miles to work is starting to feel like too much prep, for such a short ride. I always feel good, but... planning some long rides this weekend.