Noun
heat index (plural heat indexes or heat indices)
(US, meteorology) A figure used by American meteorologists to describe the apparent heat felt by a person as the result of a combination of temperature and humidity.
Mostly sunny, with a high near 90. Heat index values as high as 95. Calm wind becoming northeast 5 to 7 mph in the afternoon. Source: Internet
Heat index values nearing 100. Source: Internet