How do you determine the heat index?

Dear Tom,

How do you determine the heat index?

Sue Peron

Dear Sue,

The heat index is the apparent temperature felt by the skin rather than the actual temperature as determined by the humidity level. In hot weather, the human body normally sweats and body heat is removed by the evaporation of the sweat. The humidity level affects the rate of evaporation, which, in turn, affects the temperature the skin feels. The computation extremely complicated and calculators have been developed using inputs of temperature and relative humidity or dew point. A link to the calculator can be found at Back in the 1960s the National Weather Service’s first attempt at addressing discomfort was the implementation of the Temperature Humidity Index or THI.