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The formula below approximates the heat index in degrees Fahrenheit, to within ±1.3 °F (0.7 °C). It is the result of a multivariate fit (temperature equal to or greater than 80 °F (27 °C) and relative humidity equal to or greater than 40%) to a model of the human body.
12 Μαΐ 2022 · The Rothfusz regression is not appropriate when conditions of temperature and humidity warrant a heat index value below about 80 degrees F. In those cases, a simpler formula is applied to calculate values consistent with Steadman's results: HI = 0.5 * {T + 61.0 + [ (T-68.0)*1.2] + (RH*0.094)}
The Heat Index (or apparent temperature) is the result of extensive biometeorological studies. The parameters involved in its calculation are shown below (from Steadman, 1979).
1 Οκτ 2013 · Extensive details are given in the original paper that developed the heat index (Steadman 1979a) to describe how physiological heat-regulation principles were used to incorporate both air temperature and moisture to determine heat index values for specific weather conditions.
For example, when the temperature is 35°C and the dewpoint is 25°C, the air feels oppressively hot; whereas if the dewpoint is only 5°C, a temperature of 35° can seem almost tolerable. The index that finds current favor in the U.S. is the Steadman heat index or simply heat index.
Heat Index is calculated using this formula: where T - air temperature in Fahrengeit and RH - relative humidity in percents. If RH is less than 13% and air temperature is between 80 and 112F, the following adjustment is subtracted from HI:
HI is the heat index expressed as an apparent temperature in degrees F. If the RH is less than 13% and the temperature is between 80 and 112 degrees F, then the following adjustment is subtracted from HI: ADJUSTMENT = [ (13-RH)/4]*SQRT { [17-ABS (T-95.)]/17} where ABS and SQRT are the absolute value and square root functions, respectively.
