heat index

noun

plural heat indexes or heat indices

: a value that indicates what the ambient temperature feels like to the human body and that is derived from a calculation using air temperature and relative humidity

The most likely chances for a heat advisory are Thursday and Friday, when the heat index could approach at least 100 degrees, according to National Weather Service meteorologists …

—Julie E. Greene

The heat index is defined as a function of temperature and relative humidity. The combination of the two results in an apparent temperature that gives an idea of what the hot and humid air feels like to the average person.

—Neil MacFarquhar

Examples of heat index in a Sentence

Recent Examples on the Web

At a heat index of 105 or higher, heat exhaustion is more likely. — Janet Loehrke, USA Today, 25 June 2026

Miami’s heat index was over 100 degrees. — Claire Heddles, Miami Herald, 25 June 2026

More rain is expected on Wednesday and will likely keep our heat indices below the criteria required for a heat advisory. — Lissette Gonzalez, CBS News, 24 June 2026

Humidity will also play a role along the Gulf Coast, bringing heat index values even higher. — Kathryn Prociv, NBC news, 23 June 2026

Temperature highs will be in the low-to-mid 90s and peak afternoon heat index values at 102-107 degrees. — Garfield Hylton, The Orlando Sentinel, 22 June 2026

Temperatures will continue to climb into the mid-90s each afternoon, with heat indices in the 105 to 110 range. — Bill Kearney, Sun Sentinel, 22 June 2026

Charlotte has already experienced triple-digit heat indexes this summer. — Eva Flowe june 22, Charlotte Observer, 22 June 2026

Many of the games will have temperatures in the 80s and 90 degrees Fahrenheit range, with heat index values exceeding 100 degrees F in some cases. — Omer Awan, Forbes.com, 16 June 2026

Word History

First Known Use

1984, in the meaning defined above