Understanding the Heat Index

Recently, the term ‘heat index’ has become common in weather reports. It measures how hot the air feels when both temperature and humidity are considered. Often, the heat index is higher than the actual temperature. For instance, if the temperature in Central Park is 98 degrees, the heat index could be 105 degrees. This happens because humidity affects perspiration evaporation, making it feel hotter.

The heat index is more than just a simple measure of temperature and humidity. It’s based on an equation that takes into account these two factors. The formula involves complex calculations where specific constants are applied to the temperature and humidity values.

It’s not just the heat, it’s (T × 2.049) + (H × 10.143) – (T × H × 0.225) – (T² × 0.007) – (H² × 0.055) + (T² × H × 0.001) + (H² × T × 0.001) – (T² × H² × 0.000002) – 42.379.

The formula was developed by Lans Rothfusz, a retired meteorologist from the National Weather Service. He created it in 1990 while working as an intern at the Weather Service’s Southern Region Headquarters in Fort Worth. Rothfusz, who later received accolades such as the National Weather Association’s 2014 operational achievement award, crafted the equation that is now essential in assessing how weather conditions feel to the human body.