The heat index provides information about how hot it feels outside in the shade. It is a measure of the air temperature in relation to the relative humidity for a particular day. The temperature feels hotter when the humidity is higher.
The National Weather Service lists a heat index each day in the newspaper to alert people of the risk for a heat-related illness. Direct exposure to the sun can increase the risk for a heat-related illness on days when the heat index is high. Babies, older adults, or anyone with a health condition may have more risk of problems with the heat because of their age and general health.
Prevention measures during days of high heat index will help reduce the risk of a heat-related illness. When the outdoor humidity is high, losing body heat by sweating is not as effective, so other measures to keep cool are needed.