2017-03-06

Heat Index in Celsius

Usually someone has created and put on the net everything you might possibly want, but there doesn't seem to be a formula for heat index in Celsius yet. So here it is:

HI=
-0.000003582 * RH² * T²
0.0022117 * RH * T²
-0.0123 * T²
0.0007254 * RH² * T
-0.14611 * RH * T
1.611 * T
-0.01643 * RH²
2.34 * RH
-8.9               

where RH is relative humidity in percents, and T is temperature in Celsius. Notice that the formula stops working below ~26 °C and ~40 %.

The above is slightly prettified from the original formula, but is accurate to 0.03 °C, which should be accurate enough, considering the formula is based on subjective impressions of heat.


This corresponds with the original formula:

HI=
-0.000003582 * RH² * T²
+0.002211732 * RH * T²
-0.012308094 * T²
+0.00072546 * RH² * T
-0.14611605 * RH * T
+1.61139411 * T
-0.0164248278 * RH²
+2.3385488389 * RH
-8.7846947556

Yet another formula, that works on values less than 40 % humidity:

HI=
-1.561599e-10 * RH³ * TC³
-7.0770996e-8 * RH² * TC³
+4.6241604e-6 * RH * TC³
-1.2521304e-4 * TC³
-6.8105952e-9 * RH³ * TC²
+1.460390688e-5 * RH² * TC²
+8.68291488e-4 * RH * TC²
+0.0102724812 * TC²
+1.03391224e-7 * RH³ * TC
-2.286195888e-4 * RH² * TC
-0.07376580288 * RH * TC
+0.669176288 * TC
+1.931219745777775e-5 * RH³
-0.005028108526222222 * RH²
+1.428727636266666 * RH
-0.429784071111111

The table is from the simpler formula.

RH (%)
100 28 36 44 54 66 78 92 108 125 143 163
95 28 35 42 51 62 74 87 101 117 134 152
90 28 34 41 49 58 69 81 95 109 125 142
85 28 33 39 47 55 65 76 88 102 116 132
80 28 32 38 44 52 61 71 83 95 108 123
75 27 31 36 42 49 58 67 77 88 101 114
70 27 31 35 40 47 54 63 72 82 94 106
65 27 30 34 39 44 51 59 67 77 87 98
60 27 29 33 37 42 48 55 63 71 81 91
55 27 29 32 36 40 46 52 59 66 75 84
50 27 28 31 34 38 43 49 55 62 69 78
45 26 28 30 33 37 41 46 51 57 64 72
40 26 28 30 32 35 39 43 48 54 60 66

26 28 30 32 34 36 38 40 42 44 46 T (°C)

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