Two things are key when running in humidity. One, as
@BuckeyeBama said above, you need to slow down. Instead of running by pace, run by level of effort. Trying to maintain your normal pace in hot and/or humid conditions will be very difficult and can lead to overexertion issues. Keeping your effort the same, however, will naturally reduce your pace to a level where you can safely get your run in. The second key is to make sure you are well hydrated before and during your run. You'll be sweating more than normal, so you need to drink plenty of fluids during the day. I'd also recommend taking salt tabs for runs of over 90 minutes. They'll help replace the electrolytes you lose when sweating that much. A last point: don't push it. Don't think that just because you can run 10 miles at home means you can go right out and run 10 miles in different conditions. Be smart and safe and ease into it for a few days while you acclimate.