The heat index considers the actual temperature and amount of moisture in the air using the dew point or relative humidity.

At 2:08 p.m. on Monday, the National Weather Service released a heat advisory in effect until Tuesday at 9 p.m. for Lauderdale, Colbert, Franklin, Lawrence, Limestone, Madison, Morgan and Cullman counties.

A heat advisory has been issued for Miami-Dade and Broward counties for Monday and will be in effect noon to 6 p.m. South Florida also was under a heat advisory on Friday. Although the weekend was scorching hot in the region, the National Weather Service in Miami didn’t issue heat advisories for Saturday and Sunday.

The National Weather Service office in Mobile, Alabama, issued a heat advisory in Escambia, Santa Rosa and Okaloosa counties between 10 a.m. and 7 p.m. Monday. Heat index values are forecast to reach as high as 109℉ in portions of south central and southwest Alabama, northwest Florida and southeast Mississippi.

All of Florida will be under heat advisories Monday, July 21, as a heat dome spreads from the Ohio and Mississippi valleys. Here's what to know.

How low should you set your thermostat for as record-breaking heat sweeps over the country? Here's what experts and other Floridians say.

A heat advisory is in effect from noon until 8 p.m. Heat indices will soar up to 108° this afternoon. Isolated to scattered showers & storms are likely. Any storm that develops could produce wind gusts of 40-60 mph, heavy rainfall, and small hail. High temperatures will soar into the mid-upper 90s in the Upstate, and near 90° in the mountains.