Heat index or HI is sometimes referred to as the "apparent Temperature". The HI, given in degrees F, is a measure of how hot it feels when relative humidity (RH) is added to the actual air temperature.
Calculate the heat index using the Meteorological calculator Javascript .
HEAT INDEX CHART
AIR TEMPERATURE (F)
70 75 80 85 90 95 100 105 110 115 120 125 130
0 64 69 73 78 83 87 91 95 99 103 107 111 117
5 64 69 74 79 84 88 93 97 102 107 111 116 122
R 10 65 70 75 80 85 90 95 100 105 111 116 123 131
E 15 65 71 76 81 86 91 97 102 108 115 123 131
L 20 66 72 77 82 87 93 99 105 112 120 130 141
A 25 66 72 77 83 88 94 101 109 117 127 139
T 30 67 73 78 84 90 96 104 113 123 135 148
I 35 67 73 79 85 91 98 107 118 130 143
V 40 68 74 79 86 93 101 110 123 137 151
E 45 68 74 80 87 95 104 115 129 143
50 69 75 81 88 96 107 120 135 150
H 55 69 75 81 89 98 110 126 142
U 60 70 76 82 90 100 114 132 149
M 65 70 76 83 91 102 119 138
I 70 70 77 85 93 106 124 144
D 75 70 77 86 95 109 130
I 80 71 78 86 97 113 136
T 85 71 78 87 99 117
Y 90 71 79 88 102 122
95 71 79 89 105
(%) 100 72 80 91 108
To find the heat index value or HI, look at the heat index chart. For example, if the air temperature is 95 degrees fahrenheit (found at the top of the table) and the relative humidity or RH is 55% (found on the left side of the table). The HI, "or how hot it really feels" is 110 degrees Fahrenheit. This is at the intersection of the 95 fahrenheit row and the 55% Column.
HI = -42.379 + 2.04901523T + 10.1433127R - 0.22475541TR
- 6.83783x10 -3 T 2 - 5.481717x10 -2 R 2
+ 1.22874x10 -3 T 2R + 8.5282x10 -4 TR 2
- 1.99x10 -6 T 2 R 2
where
References
Rothfusz, L. P., 1990:The heat index equation (or, more than you ever wanted to
know about heat index). NWS Southern Region Technical Attachment, SR/SSD 90-23,
Fort Worth, TX.
Last modified 05/31/96