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.

Heat advisory issued by NWS Jacksonville for high heat index values up to 110 in parts of Florida and Georgia.

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.

The National Weather Service says heat indices as high as 114 are possible in Panama City and issued an advisory. Meanwhile an Atlantic system brews.

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

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

The National Weather Service has issued another heat advisory for Central Florida, which includes Walt Disney World and Universal Orlando.