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
In fact, the high temperature today in Surprise (updated from the time your question was initially posed) is expected to be 101 degrees, with a heat index of 103.
—Jon Wilner, Mercury News, 23 May 2025
Meteorologist Ivan Cabrera forecasts low- to mid- 90s Thursday with a heat index in the triple digits.
—Howard Cohen, Miami Herald, 22 May 2025
Temperature highs will be in the low-to-mid 90s with a peak afternoon heat index between 100 and 105 degrees, according to NWS Melbourne.
—Garfield Hylton, The Orlando Sentinel, 20 May 2025
Across central and southern Texas, heat index values — a measure of what conditions feel like when air temperatures and humidity are combined — will range from 105 degrees to 108 degrees Fahrenheit on Thursday.
—Denise Chow, NBC news, 15 May 2025
Elsewhere in the state, heat index values up to 112 were forecast for inland Kleberg, Nueces, and San Patricio Counties on Wednesday.
—Joe Edwards, MSNBC Newsweek, 13 May 2025
Humidity will pick up toward the weekend as well, bringing heat indices up to the triple digits in the interior.
—Bill Kearney, Sun Sentinel, 12 May 2025
Warm temperatures will continue through Wednesday, with some locations west of Cumberland Plateau Region experiencing heat index values up to around 105 degrees.
—Diana Leyva, The Tennessean, 5 Aug. 2024
The scientists then compared shifts in people’s biological age to the historical heat index readings of their location and the number of heat days recorded by the National Weather Service’s Heat Index Chart between 2010 and 2016.
—Brian Mastroianni, Health, 10 Mar. 2025
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Jon Wilner, Mercury News, 23 May 2025
Meteorologist Ivan Cabrera forecasts low- to mid- 90s Thursday with a heat index in the triple digits.
—Howard Cohen, Miami Herald, 22 May 2025
Temperature highs will be in the low-to-mid 90s with a peak afternoon heat index between 100 and 105 degrees, according to NWS Melbourne.
—Garfield Hylton, The Orlando Sentinel, 20 May 2025
Across central and southern Texas, heat index values — a measure of what conditions feel like when air temperatures and humidity are combined — will range from 105 degrees to 108 degrees Fahrenheit on Thursday.
—Denise Chow, NBC news, 15 May 2025
Elsewhere in the state, heat index values up to 112 were forecast for inland Kleberg, Nueces, and San Patricio Counties on Wednesday.
—Joe Edwards, MSNBC Newsweek, 13 May 2025
Humidity will pick up toward the weekend as well, bringing heat indices up to the triple digits in the interior.
—Bill Kearney, Sun Sentinel, 12 May 2025
Warm temperatures will continue through Wednesday, with some locations west of Cumberland Plateau Region experiencing heat index values up to around 105 degrees.
—Diana Leyva, The Tennessean, 5 Aug. 2024
The scientists then compared shifts in people’s biological age to the historical heat index readings of their location and the number of heat days recorded by the National Weather Service’s Heat Index Chart between 2010 and 2016.
—Brian Mastroianni, Health, 10 Mar. 2025
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 5 Jun. 2025.
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