Condensation can be a sign of high humidity. When warm, humid air contacts a cold surface, condensation may form. (To see this, remove a cold bottle of water from a refrigerator and take it outside on a hot day. Typically, condensation will form on the outside of the bottle.) Humidity can be measured with a humidity gauge or meter; models that can monitor both temperature and humidity are generally available for less than $50 at hardware stores or on the Internet.