In recent days, discussions about a discomfort metric known as the heat index have become common. This measure aims to evaluate how hot the air feels by considering both temperature and humidity.

The heat index often shows a higher number than the actual temperature. For instance, while the temperature in Central Park may be 98 degrees, the heat index might be 105. The reason for this discrepancy is that increased humidity impairs the evaporation of sweat from the skin, making the air feel warmer.

What Is the Heat Index?

The heat index is a more detailed way of saying, “it’s not just the heat, but the humidity.” The formula involves variables of temperature (T) and relative humidity (H) in a complex equation:

“(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”

Origin of the Heat Index

The equation was developed by Lans Rothfusz, a former National Weather Service meteorologist. Mr. Rothfusz created the heat index formula in 1990 during his time as an intern at the Weather Service’s Southern Region Headquarters in Fort Worth. His work on the heat index has been recognized, earning him the National Weather Association’s operational achievement award in 2014.

This calculation provides a more accurate representation of how people experience heat, especially in conditions where high humidity is present. It highlights the important role humidity plays in altering perceived temperature, which can be critical for understanding weather conditions and planning.