Is relative humidity or dew point a better indicator of the feeling of humidity?
Dew point, a direct measure of atmospheric moisture, is a much better indicator of discomfort than relative humidity. It is a conservative feature, meaning it remains reasonably constant during the day, barring a change of air mass. In contrast, relative humidity can vary tremendously during the day, often by 70 percent or more. It’s usually highest at daybreak and lowest in the mid-afternoon. Most people begin to feel some discomfort when the dew point approaches 65, and by the time it climbs to 75, almost everyone is uncomfortable. Chicago’s record-high dew point, a steamy 83, was recorded on July 30, 1999. The world’s highest dew points have reached the middle 90s and have been reported near the very warm waters of the Red Sea and the Persian Gulf.