You need to make sure your body is acclimated to the temperature and humidity, which can take about 2 weeks if you're in good condition, so take it easy at first. The problem with high humidity is that you can't perspire and have it evaporate, so you will overheat. If you can change clothing to allow drier clothes then that will help, but even staying hydrated won't help in high heat with high humidity. Give yourself some time to acclimate, but if you start feeling dizzy or sick, or bad in any way, stop and get out of the heat immediately as it can be dangerous.

If you have access to a local school, check with their Athletic Trainer to see what recommendations he/she has for their athletes as that should transfer to you too.