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

Forecasters also warned that dangerous heat will build across the Southeast into the week, with heat indices potentially exceeding 110 degrees. — Thao Nguyen, USA Today, 20 July 2026

Temperatures reached as high as 102 degrees in Texarkana with a heat index value of 117. — Miceala Morano, Arkansas Online, 20 July 2026

Charlotte reached a high of 98 on Friday and a heat index of 103, NWS meteorologist Chris Horne said Saturday. — Joe Marusak, Charlotte Observer, 18 July 2026

Temperatures are gong to be in the low-to-mid 90s across the region, with peak heat indices ranging from 100 to 107 degrees. — Garfield Hylton, The Orlando Sentinel, 17 July 2026

Word History

First Known Use

1984, in the meaning defined above