How to use in-sentence of “heat index”:
+ The humidex differs from the heat index in using the dew point rather than the relative humidity.
+ The humidex differs from the heat index used in the United States, in being derived from the dew point rather than the relative humidity.
+ The heat index and humidex figures are based on temperature measurements taken in the shade and not the sun, so extra care must be taken while in the sun.
+ The heat index is defined so as to equal the actual air temperature when the partial pressure of water vapor is equal to a baseline value of 1.6 kPa.
+ When the temperature felt outside is higher than the real temperature, the heat index is used.
+ Sometimes the heat index and the wind chill are denoted collectively by the single terms “apparent temperature” or “relative outdoor temperature”.
+ The heat index is calculated only if the actual temperature is above 27 °C, and relative humidities higher than 40%.
+ The heat index was developed in 1978 by George Winterling as the “humiture” and was adopted by the National Weather Service a year later.