Sounds like typical humidity problems. Normally you'll see humidity on the ends of the lenses (or inside it even).
The best thing to do when shooting or dealing with Humidity is to open the body, remove the lens and its caps, about 15-20 minutes prior to going out to shoot. The humidity will clear up, and everything'll be good. Don't use a cloth to clean the lens, as it'll just make it harder to clean up in the end and won't deal with the humidity problem.
I've had this problem...many times, in Puerto Rico, Acapulco, Miami, works every time.
Chances are that it isn't a problem, and if it isn't affecting your final shots, i wouldn't worry about it.