What does the "heat index" measure?

The heat index measures the perceived temperature, which is a combination of the actual air temperature and the relative humidity. This index reflects how hot it actually feels to the human body, as our perception of temperature can be significantly impacted by humidity levels. When humidity is high, sweat does not evaporate as quickly, making it feel hotter than the actual air temperature. This makes the heat index particularly important in weather forecasting, as it helps to communicate heat-related risks and advisories, especially during hot weather when humidity levels can elevate the risk of heat-related illnesses. Understanding the heat index is critical for both safety and comfort in warm climates.