Temperatures that hover 10 degrees or more above the average high temperature for a region and lasts for several weeks are defined as extreme heat. Humid or muggy conditions, which add to the discomfort of high temperatures, occur when a "dome" of high atmospheric pressure traps hazy, damp air near the ground. Droughts occur when a long period passes without substantial rainfall. A heat wave combined with a drought is a very dangerous situation.
During an ordinary Florida summer, outdoor high temperatures average near 90 degrees, and combined with the normally high humidity's, produce a "heat index" (the temperature that it feels like) which averages around 100 degrees. But the heat indices can exceed the danger category of 105 degrees for several days in a row. When this extreme heat is expected the National Weather Service will issue heat advisories to alert the public to the danger.