Apparent Temperature Heat Index

First posted on the 1st July, 2012 – IT
Last modified on the 1st July, 2012, at 7:07 pm

Was looking around for an index to some how combine the influence of relative humidity on temperature and came across the heat index of apparent temperature (TA). The apparent temperature is calculated from the temperature in Fahrenheit or Celsius and relative humidity in percent using the following empirical equation:

TA = c0 + c1 T + c2 H + c3 TH + c4 T2 + c5 H2 + c6 HT2 + c7 TH2 + c8 T2H2

The proportionality constants for calculation in both Celsius and Fahrenheit are:

TA °F TA °C
c0 -4.238 × 10+1 -8.786
c1 +2.049 +1.611
c2 +1.014 × 10+1 +2.335
c3 -2.248 × 10-1 -0.146 × 10-2
c4 -6.838 × 10-3 -1.231 × 10-2
c5 -5.482 × 10-2 +1.643 × 10-2
c6 +1.228 × 10-3 +2.210 × 10-3
c7 +8.528 × 10-4 +7.254 × 10-4
c8 -1.995 × 10-6 -3.582 × 10-6

Proportionality constants for Celsius were calculated from those given for Fahrenheit using the standard conversion from Celsius to Fahrenheit and simplifying.

The relationship between apparent and the true temperature and humidity is best shown in a contour plot:

The current apparent temperature is now also reported along with actual temperature and humidity. When I get around to updating the temperature history logs the apparent temperature will also be logged.