The Heat Index (HI), also known as the "apparent temperature" or "feels-like temperature," is a measure of how hot it feels when relative humidity is factored in with the actual air temperature. It takes into account both the air temperature and the level of humidity to provide a more accurate representation of how the human body perceives the temperature.
The formula used to calculate the Heat Index is based on the heat stress experienced by the human body. When the air is humid, it can hinder the body's ability to cool down through the evaporation of sweat, making it feel hotter than the actual air temperature. On the other hand, in dry conditions, the body's natural cooling mechanism is more effective, and the apparent temperature may be closer to the actual air temperature.
The exact formula for calculating the Heat Index varies from one region to another, but it generally involves using the air temperature and relative humidity to compute the apparent temperature. The result is usually expressed in degrees Fahrenheit or degrees Celsius.
Heat Index warnings and advisories are often issued by meteorological agencies to help people take precautions during hot and humid conditions, as high heat indices can increase the risk of heat-related illnesses. It's important to stay hydrated, stay cool, and take precautions when the Heat Index is elevated, especially during hot and humid weather.