Thursday was plagued by heat advisories across much of Florida. The entire peninsula, covering more than 50 counties, was under a Heat Advisory, meaning that between 11 a.m. and 7 p.m., temperatures would be dangerously high, with heat indices reaching as high as 111°F. The culprit behind this extreme heat is a high-pressure system that brings sinking air over Florida. As the air sinks, it compresses and warms.