I live in south central Alabama. We have high heat and high humidity. I've found that the high humidity negates a lot of options, especially on a fully faired bike like a Spyder RT or my old BMW R1100RT. There's very little air flow.
Because of the humidity, I've found that artificial fabrics like mesh Cordura and Under Armor-type clothing don't wick well. I also have an evaporative cooling vest, but it's only good for about 30 minutes, after which time it works its way up to match the outside temperature and I feel like I'm wearing a warm wet blanket, and it no longer cools.
Over the years I've found that cotton works best for me down here during the summer. It wicks and absorbs moisture away from my skin. so I wear
Diamond Gusset Defender jeans with kevlar cloth at the butt, hips, and knees. Lately on really hot days, I've taken to wearing just a long-sleeved, cotton shirt. If it's tad cooler, I'll wear a cotton t-shirt under a
Draggin' Jeans kevlar mesh shirt. My choice of gear obviously lacks impact pads, but I figure the kevlar will at least minimize road rash if I slide. I always wear gloves, boots, and a full-face helmet.
For the cooler times, I have a two-piece Aerostich Roadcrafter. I wear the jacket and Defender jeans a lot; the Roadcrafter pants only if it's really chilly/wet.
As a matter of fact, I went for a ride today and the temperature was 95 degrees, and showers gradually built up, so the humidity was way up there -- as usual.
Updated: I should add that, while I've read of good results of an evaporative vest under a mesh jacket, the price of mesh jackets makes this an expensive experiment, IMO.