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
On Thursday, high temperatures will rise into the low 90s with plenty of sunshine, and heat indices will reach the mid- to upper 90s.
—Lissette Gonzalez, CBS News, 6 May 2026
The demonstration on Friday, with a heat index projected to hit 100 degrees, kicked off Miami-Dade’s heat season, which now arrives earlier, lasts longer and is more intense because of climate change.
—Ashley Miznazi, Miami Herald, 4 May 2026
Highs in the mid 90s inland by Thursday, heat index near 100.
—Bill Kearney, Sun Sentinel, 4 May 2026
The highest actual temperatures and heat indices are forecast for Saturday.
—Sarah Perkel, USA Today, 1 May 2026
Monday and Tuesday could be a few degrees warmer, with heat index values of up to 102 degrees possible.
—Anthony Franze, San Antonio Express-News, 24 Apr. 2026
The change will ensure these households can use fans or air conditioners when the NWS issues heat indexes of 95 degrees Fahrenheit or above.
—Sophie Hartley, IndyStar, 27 Feb. 2026
The Marines worked in hot, humid conditions with a heat index above 100 degrees.
—Erika I. Ritchie, Oc Register, 27 Nov. 2025
In 2024, Miami-Dade County experienced 60 full days with heat indexes greater than 105 degrees Fahrenheit.
—Vann R. Newkirk Ii, The Atlantic, 10 Nov. 2025
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Lissette Gonzalez, CBS News, 6 May 2026
The demonstration on Friday, with a heat index projected to hit 100 degrees, kicked off Miami-Dade’s heat season, which now arrives earlier, lasts longer and is more intense because of climate change.
—Ashley Miznazi, Miami Herald, 4 May 2026
Highs in the mid 90s inland by Thursday, heat index near 100.
—Bill Kearney, Sun Sentinel, 4 May 2026
The highest actual temperatures and heat indices are forecast for Saturday.
—Sarah Perkel, USA Today, 1 May 2026
Monday and Tuesday could be a few degrees warmer, with heat index values of up to 102 degrees possible.
—Anthony Franze, San Antonio Express-News, 24 Apr. 2026
The change will ensure these households can use fans or air conditioners when the NWS issues heat indexes of 95 degrees Fahrenheit or above.
—Sophie Hartley, IndyStar, 27 Feb. 2026
The Marines worked in hot, humid conditions with a heat index above 100 degrees.
—Erika I. Ritchie, Oc Register, 27 Nov. 2025
In 2024, Miami-Dade County experienced 60 full days with heat indexes greater than 105 degrees Fahrenheit.
—Vann R. Newkirk Ii, The Atlantic, 10 Nov. 2025
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 11 May. 2026.
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