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
Julie E. GreeneThe 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
Neil MacFarquharExamples of heat index in a Sentence
Recent Examples on the Web
Peak heat index values are between 99 and 104 degrees.
—Garfield Hylton, The Orlando Sentinel, 7 July 2025
The high Tuesday will be near 92 degrees and heat index values are set to be as high as 102 degrees.
—arkansasonline.com, 7 July 2025
Northeast and southeast portions of North Dakota could see heat index values up to 101, the NWS said.
—Joe Edwards, MSNBC Newsweek, 4 July 2025
Temperatures are expected to be around 92 degrees, with heat index values in the mid- to upper 90s, according to the weather service.
—Kansas City Star, 3 July 2025
Surface dew points will likely reach near 70 on Saturday, July 5, which limits the maximum heat index values to below 100.
—Haadiza Ogwude, The Enquirer, 3 July 2025
Officials have been preparing as Indianapolis is expected to experience heat indices of up to 103 degrees until June 24, the city said.
—Matthew Cupelli, IndyStar, 2 July 2025
What’s the difference between temperature and heat index?
—Brandi D. Addison, Austin American Statesman, 2 July 2025
The early-summer heatwave continues in the Chicago area, with the National Weather Service forecasting more air temperatures in the 90s and even hotter heat indices, and public health leaders urging caution.
—Jessi Virtusio, Chicago Tribune, 1 July 2025
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Garfield Hylton, The Orlando Sentinel, 7 July 2025
The high Tuesday will be near 92 degrees and heat index values are set to be as high as 102 degrees.
—arkansasonline.com, 7 July 2025
Northeast and southeast portions of North Dakota could see heat index values up to 101, the NWS said.
—Joe Edwards, MSNBC Newsweek, 4 July 2025
Temperatures are expected to be around 92 degrees, with heat index values in the mid- to upper 90s, according to the weather service.
—Kansas City Star, 3 July 2025
Surface dew points will likely reach near 70 on Saturday, July 5, which limits the maximum heat index values to below 100.
—Haadiza Ogwude, The Enquirer, 3 July 2025
Officials have been preparing as Indianapolis is expected to experience heat indices of up to 103 degrees until June 24, the city said.
—Matthew Cupelli, IndyStar, 2 July 2025
What’s the difference between temperature and heat index?
—Brandi D. Addison, Austin American Statesman, 2 July 2025
The early-summer heatwave continues in the Chicago area, with the National Weather Service forecasting more air temperatures in the 90s and even hotter heat indices, and public health leaders urging caution.
—Jessi Virtusio, Chicago Tribune, 1 July 2025
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 17 Jul. 2025.
Copy CitationLove words? Need even more definitions?
Merriam-Webster unabridged
Share