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Heat Index
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 .
The following equation approximates the Heat Index. There are many assumptions made
produce this, far too many to list here. The equation was obtain by multiple
regression analysis and there is a +-1.3 degree oF error.
HI = -42.379 + 2.04901523T + 10.14333127R - 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
- T = ambient dry bulb temperature degrees Farhrenheit
- R = relative humidity
-
| HEAT INDEX °F (°C) |
| |
RELATIVE HUMIDITY (%) |
| Temp. |
40 |
45 |
50 |
55 |
60 |
65 |
70 |
75 |
80 |
85 |
90 |
95 |
100 |
110
(47) |
136
(58) |
|
|
|
|
|
|
|
|
|
|
|
|
108
(43) |
130
(54) |
137
(58) |
|
|
|
|
|
|
|
|
|
|
|
106
(41) |
124
(51) |
130
(54) |
137
(58) |
|
|
|
|
|
|
|
|
|
|
104
(40) |
119
(48) |
124
(51) |
131
(55) |
137
(58) |
|
|
|
|
|
|
|
|
|
102
(39) |
114
(46) |
119
(48) |
124
(51) |
130
(54) |
137
(58) |
|
|
|
|
|
|
|
|
100
(38) |
109
(43) |
114
(46) |
118
(48) |
124
(51) |
129
(54) |
136
(58) |
|
|
|
|
|
|
|
98
(37) |
105
(41) |
109
(43) |
113
(45) |
117
(47) |
123
(51) |
128
(53) |
134
(57) |
|
|
|
|
|
|
96
(36) |
101
(38) |
104
(40) |
108
(42) |
112
(44) |
116
(47) |
121
(49) |
126
(52) |
132
(56) |
|
|
|
|
|
94
(34) |
97
(36) |
100
(38) |
103
(39) |
106
(41) |
110
(43) |
114
(46) |
119
(48) |
124
(51) |
129
(54) |
135
(57) |
|
|
|
92
(33) |
94
(34) |
96
(36) |
99
(37) |
101
(38) |
105
(41) |
108
(42) |
112
(44) |
116
(47) |
121
(49) |
126
(52) |
131
(55) |
|
|
90
(32) |
91
(33) |
93
(34) |
95
(35) |
97
(36) |
100
(38) |
103
(39) |
106
(41) |
109
(43) |
113
(45) |
117
(47) |
122
(50) |
127
(53) |
132
(56) |
88
(31) |
88
(31) |
89
(32) |
91
(33) |
93
(34) |
95
(35) |
98
(37) |
100
(38) |
103
(39) |
106
(41) |
110
(43) |
113
(45) |
117
(47) |
121
(49) |
86
(30) |
85
(29) |
87
(31) |
88
(31) |
89
(32) |
91
(33) |
93
(34) |
95
(35) |
97
(36) |
100
(38) |
102
(39) |
105
(41) |
108
(42) |
112
(44) |
84
(29) |
83
(28) |
84
(29) |
85
(29) |
86
(30) |
88
(31) |
89
(32) |
90
(32) |
92
(33) |
94
(34) |
96
(36) |
98
(37) |
100
(38) |
103
(39) |
82
(28) |
81
(27) |
82
(28) |
83
(28) |
84
(29) |
84
(29) |
85
(29) |
86
(30) |
88
(31) |
89
(32) |
90
(32) |
91
(33) |
93
(34) |
95
(35) |
80
(27) |
80
(27) |
80
(27) |
81
(27) |
81
(27) |
82
(28) |
82
(28) |
83
(28) |
84
(29) |
84
(29) |
85
(29) |
86
(30) |
86
(30) |
87
(31) | |
| Category |
Heat Index |
Possible heat disorders for people in high risk groups |
Extreme
Danger |
130°F or higher
(54°C or higher) |
Heat stroke or sunstroke likely. |
| Danger |
105 - 129°F
(41 - 54°C) |
Sunstroke, muscle cramps, and/or heat exhaustion likely. Heatstroke possible with prolonged exposure
and/or physical activity. |
Extreme
Caution |
90 - 105°F
(32 - 41°C) |
Sunstroke, muscle cramps, and/or heat exhaustion possible with prolonged exposure and/or physical
activity. |
| Caution |
80 - 90°F
(27 - 32°C) |
Fatigue possible with prolonged exposure and/or physical activity.
|
|
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.
Questions or comments about these pages? Send to Ron Murphy
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