I live down here in sunny FL, and I hike/bike/camp year-round. From the lows in the twenties during our week of winter here to 95+ degrees with 100% humidity during May to October, I do it all. It helps that I tend to bike to the campsite; you always have a breeze on a bike.
Even so, I hiked the Ocala South section of the FL Trail last August. It was when I could get two days off from work. I didn't see anyone on the trail outside of the established campgrounds (water stops), and it was wonderful for that.
I highly recommend going out during the "off" seasons for your area if you want to be alone on larger trails. As long, of course, as you have the skill set to deal with problems under those conditions (be they heat or cold).

