heat index

[ heet in-deks ]

noun

, Meteorology.

1. a formulaically calculated approximation of how hot it feels given the temperature of the air combined with the relative humidity, based on the fact that an actual temperature will feel warmer as the relative humidity rises and causes a decrease in the natural evaporative cooling from perspiration. : HI, H.I.

heat index

1. A measurement of the air temperature in relation to the relative humidity, used as an indicator of discomfort. The heat index is higher when high air temperatures occur with high humidity, and lower when they occur with low humidity. The heat index is based on studies of skin cooling caused by the evaporation of sweat.
2. Also called apparent temperature

Word History and Origins

Origin of heat index¹

First recorded in 1975–80

Example Sentences

The heat index — a measure that includes temperature and humidity to showcase how hot it actually feels — topped 100 degrees in some areas, and temperatures reached as high as 95 degrees in cities like Bangor, Houlton and Millinocket, according to the National Weather Service.

From New York Times

The heat index in western Pennsylvania has been in the 90s, and could reach over 100 degrees this week.

From New York Times

See detailed maps about the latest heat index forecasts.

From New York Times

The heat index — a combination of air temperature and humidity to indicate how the heat feels to the human body — neared triple digits in parts of south Texas on Monday.

From Seattle Times

Miami hit a record high temperature for the date of 96℉ on Sunday, and the heat index near the Texas-Mexico border is expected to near 120℉ on Monday.

From Salon