I got a really nice Scorpion Cool Rod mesh jacket for Father's Day.  It is very light and flows great.  Wore it the other day about 90+ no problem at all.   Don't know about the "almost 100 with 90 percent humidity" days we have here in East NC, but don't know of any jacket that is great for those days.   The quality of the jacket is very very excellent.   I got the white/black which is great for increased visibility now that my bike is black instead of Hemi orange.   For about a buck 50 this is a great deal.   

glad to hear you found one that you like.  And i hear ya on the almost 100 and 90% humidity days, not much you can do besides jump in a fountain and bee damp and cool for the next 20 minutes of riding 

I've got a Tourmaster/Cortech HRX mesh jacket bought from newenough.com (it has since been discontinued/replaced with a newer versions) and it flows a lot of air. It's also got CE armor in the elbows, shoulders, and back along with leather in those same impact areas.
Tony

I sold my old triumph summer jacket after I sold my bike and didn't think I would be riding, which I wish I hadn't done. It was one of the nicest summer jackets I'd seen. I can't imagine some of the cheaper summer jackets doing much of anything in a crash.

I think it actually felt good to wear the mesh jacket in summer, because any time I'd stop at a light I'd start to sweat a little bit, then when I'd get moving I'd feel way cooler than if I had on a t shirt and wasn't sweating anyway.