How does increased moisture impact the heat index?

Increased moisture in the atmosphere directly impacts the heat index by making it feel warmer than the actual temperature. The heat index is essentially a measure of how hot it feels when humidity is factored in with the actual air temperature. When humidity levels rise, sweat on the skin evaporates less efficiently, which is the body's natural cooling mechanism. As a result, the body retains more heat and feels warmer than the standard air temperature might suggest.

This effect is particularly important in hot weather where high humidity can lead to uncomfortable and potentially dangerous heat stress conditions. Therefore, as moisture in the air increases, the heat index rises significantly, indicating a higher perceived temperature which reflects the combined effect of heat and humidity on the human experience.