I also live in a hot and humid area and I'm also dealing with this now (and for the past 20 years). As Gator rate said, some tech/calcs can help you account for it, but others don't consider temps/humidity.
For me, my cool weather "bottom of zone 2 pace" stays in my zone 2 heart rate range (rising, but staying below zone 3), even if I go for two hours in zone two with no fluids. In the summer here, I'm dealing with temps above 80 degrees even early in the morning and high humidity as well. I can only run at the bottom of zone 2 pace for about an hour before my heart rate starts threatening zone 3. Sooo, if I'm out there for an hour or less, I pretty much just run my zone 2 pace. For a long run, I'll probably start a bit slower and tolerate popping into zone 3 at the end. Also, I pretty much cap my summer long runs at 2 hours just because it's just so miserable.