The heat index (HI) is an index that combines air temperature and relative humidity, in shaded areas, to posit a human-perceived equivalent temperature, as how hot it would feel if the humidity were some other value in the shade. The result is also known as the "felt air temperature", "apparent temperature", "real feel" or "feels like". --Wikipedia August 2nd, 2020.
The following tool uses the formula developed by the U.S. National Oceanic and Atmospheric Administration. The Heat Index effect goes from 26° Celsius (79 Fahrenheit) to 43° Celsius (110 Fahrenheit).
| Celsius | Note |
| 26-32 | Caution: fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps. |
| 32-41 | Extreme caution: heat cramps and heat exhaustion are possible. Continuing activity could result in heat stroke. |
| 41-54 | Danger: heat cramps and heat exhaustion are likely; heat stroke is probable with continued activity. |
| +54 | Extreme danger: heat stroke is imminent. |
Note: Exposure to full sunshine can increase heat index values by up to 8 °C (14 °F).