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
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
Friday forecast High: 96 Low: 76 Partially cloudy skies with a maximum heat index of 104 degrees.
—Bianca Moreno-Paz, Austin American-Statesman, 16 Sep. 2024
Sunday High: 95 Low: 75 Low chances of rain, with a maximum heat index of 103 degrees.
—Bianca Moreno-Paz, Austin American-Statesman, 10 Sep. 2024
The study used heat index, rather than just air temperature, to take relative humidity into account, Ailshire noted in the release.
—Khloe Quill, Fox News, 5 Mar. 2025
Wednesday forecast High: 96 Low: 75 Partly cloudy skies with a heat index up to 104 degrees.
—Bianca Moreno-Paz, Austin American-Statesman, 16 Sep. 2024
Based on the weekend's temperatures, this year’s festival had an average high of 93 degrees with heat indexes stretching into triple digits in the blazing sun, hotter than any previous Bonnaroo’s average temperature for more than 10 years.
—Melonee Hurt, Nashville Tennessean, 17 June 2024
Schools with no air conditioning in gyms that are hotter than the outside heat index play PE-style games around desks in cooler classrooms.
—Bill Frist, Forbes, 22 Jan. 2025
In Caribou, Maine, for example, the NWS issued its first-ever excessive heat warning for a heat index near 110°F on June 19.
—Andrew Freedman, Axios, 15 Jan. 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.
Brian Mastroianni, Health, 10 Mar. 2025
Friday forecast High: 96 Low: 76 Partially cloudy skies with a maximum heat index of 104 degrees.
—Bianca Moreno-Paz, Austin American-Statesman, 16 Sep. 2024
Sunday High: 95 Low: 75 Low chances of rain, with a maximum heat index of 103 degrees.
—Bianca Moreno-Paz, Austin American-Statesman, 10 Sep. 2024
The study used heat index, rather than just air temperature, to take relative humidity into account, Ailshire noted in the release.
—Khloe Quill, Fox News, 5 Mar. 2025
Wednesday forecast High: 96 Low: 75 Partly cloudy skies with a heat index up to 104 degrees.
—Bianca Moreno-Paz, Austin American-Statesman, 16 Sep. 2024
Based on the weekend's temperatures, this year’s festival had an average high of 93 degrees with heat indexes stretching into triple digits in the blazing sun, hotter than any previous Bonnaroo’s average temperature for more than 10 years.
—Melonee Hurt, Nashville Tennessean, 17 June 2024
Schools with no air conditioning in gyms that are hotter than the outside heat index play PE-style games around desks in cooler classrooms.
—Bill Frist, Forbes, 22 Jan. 2025
In Caribou, Maine, for example, the NWS issued its first-ever excessive heat warning for a heat index near 110°F on June 19.
—Andrew Freedman, Axios, 15 Jan. 2025
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 4 May. 2025.
Copy CitationLove words? Need even more definitions?
Merriam-Webster unabridged
Share