When the weather turns sultry, we see and hear references to the “heat index’” For example, this was the forecast on the Treasure Coast for Sunday, June 30th: “Showers and thunderstorms after 11 a.m. High near 92. Heat index values as high as 101.” What the heck is the heat index? The heat index combines air temperature and relative humidity in a formula to determine how hot it feels to us. Heat is removed from the body through evaporation – that is, perspiring. But when the humidity is high, evaporation is blocked, and we experience the sensation of being “hot and sticky.” You can determine the heat index by going online. Just put “heat index” in a search box and click on a link to a heat index chart. You’ll see that when the air temperature is 90 and the relative humidity is 50 percent, the heat index is 95. When the temp is 94 and the humidity is 60, the heat index is 105. And when the temp is 96 and the humidity is 75, the heat index is a whopping 132. In which case, stay inside where it’s air conditioned. The heat index is a valid measurement and has the National Weather Service seal of approval. On many days this summer, the heat index has been higher in the Northeast and Midwest than it has been on the Treasure Coast. Lucky us. For 88.9 FM, this is Paul Janensch.