Heat Index vs. Humidity
The influence of humidity on the apparent temperature and the heat index.
The Heat Index - or the Apparent Temperature - is used to indicate how hot it feels when relative humidity is combined with temperature.
With increased humidity it feels hotter as indicated in the Heat Index table bellow:
| Heat Index | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dry Temperature | Relative Humidity (%) | |||||||||||
| (oF) | (oC) | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 |
| 70 | 21.1 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 70 | 71 | 71 | 72 |
| 75 | 23.9 | 69 | 70 | 72 | 73 | 74 | 75 | 76 | 77 | 78 | 79 | 80 |
| 80 | 26.7 | 73 | 75 | 77 | 78 | 79 | 81 | 82 | 85 | 86 | 88 | 91 |
| 85 | 29.4 | 78 | 80 | 82 | 84 | 86 | 88 | 90 | 93 | 97 | 102 | 108 |
| 90 | 32.2 | 83 | 85 | 87 | 90 | 93 | 96 | 100 | 106 | 113 | 122 | |
| 95 | 35 | 87 | 90 | 93 | 96 | 101 | 107 | 114 | 124 | 136 | ||
| 100 | 37.8 | 91 | 95 | 99 | 104 | 110 | 120 | 132 | 144 | |||
| 105 | 40.6 | 95 | 100 | 105 | 113 | 123 | 135 | 149 | ||||
| 110 | 43.3 | 99 | 105 | 112 | 123 | 137 | 150 | |||||
| 115 | 46.1 | 103 | 111 | 120 | 135 | 151 | ||||||
| 120 | 48.9 | 107 | 116 | 130 | 148 | |||||||
Heat and Humidity Index Danger Zones
- 90 - 104 : Heat cramps or heat exhaustion possible
- 105 - 130 : Heat cramps or heat exhaustion likely, heatstroke possible
- 130 and more : Heat stroke highly likely
Example - Apparent Temperature
From the table - with dry temperature 85 oF and relative humidity 80% - the apparent temperature - or Heat Index - is 97 oF.
