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
Washout or not, expect above average temperatures around 90 or just above with a heat index of 100 during the day on Monday, according to the weather service.
—Howard Cohen, Miami Herald, 10 June 2026
Hot and humid conditions are expected to push afternoon temperatures into the upper 80s and lower 90s, with heat index values climbing to the 96-102 range.
—Paula Wethington, CBS News, 10 June 2026
Temperatures are expected to reach around 88 degrees, with heat index values climbing to the mid-90s, according to the weather service.
—Kansas City Star, 10 June 2026
Heat advisories are in effect for dozens of states from Minnesota down to Mississippi, as heat index values, or what the temperatures feel like, are expected to reach 100 to 110 degrees.
—Melissa Griffin, ABC News, 9 June 2026
New York City is heading into its hottest stretch of weather since July, with forecasters signaling a multi-day warming trend that could push temperatures into the lower 90s by midweek and drive heat indices near 100 later in the week.
—Brandi D. Addison, USA Today, 8 June 2026
Afternoon heat index may reach 100 on Thursday afternoon along the I-95 corridor.
—Doris Alvarez Cea, Florida Times-Union, 6 May 2026
Highs in the mid 90s inland by Thursday, heat index near 100.
—Bill Kearney, Sun Sentinel, 4 May 2026
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Howard Cohen, Miami Herald, 10 June 2026
Hot and humid conditions are expected to push afternoon temperatures into the upper 80s and lower 90s, with heat index values climbing to the 96-102 range.
—Paula Wethington, CBS News, 10 June 2026
Temperatures are expected to reach around 88 degrees, with heat index values climbing to the mid-90s, according to the weather service.
—Kansas City Star, 10 June 2026
Heat advisories are in effect for dozens of states from Minnesota down to Mississippi, as heat index values, or what the temperatures feel like, are expected to reach 100 to 110 degrees.
—Melissa Griffin, ABC News, 9 June 2026
New York City is heading into its hottest stretch of weather since July, with forecasters signaling a multi-day warming trend that could push temperatures into the lower 90s by midweek and drive heat indices near 100 later in the week.
—Brandi D. Addison, USA Today, 8 June 2026
Afternoon heat index may reach 100 on Thursday afternoon along the I-95 corridor.
—Doris Alvarez Cea, Florida Times-Union, 6 May 2026
Highs in the mid 90s inland by Thursday, heat index near 100.
—Bill Kearney, Sun Sentinel, 4 May 2026
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 12 Jun. 2026.
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