The system has now graduated to Category 2 hurricane status and is expected to reach Category 3 (with winds in excess of 110 mph) when it makes its US mainland landfall on Wednesday afternoon. The storm was centered about 365 miles south of Apalachicola and 395 miles south of Panama City, Florida.
The consensus of the various meteorological models is that the track of Michael will cross the state southeast of Laurens County, but the county is well within the storm's so-called "cone of uncertainty".
Landfall is expected Wednesday on the northeastern Gulf Coast, where authorities warned of a potentially devastating strike.
The Republican governor, who is campaigning for a US Senate seat in the November congressional elections, warned of the potential for a deadly storm surge that could be as much as 12 feet (3.7 meters) above normal sea water levels. With Michael's winds projected to be even stronger, residents there were urged to evacuate inland.
Hurricane Michael will influence South Florida's weather for the rest of the week, but the effects are not expected to be significant, forecasters say.
The storm's center and where it makes landfall with its destructive winds represent just one of several concerns.
However, the cold front should pick up Michael as it moves north, and kick the center of it out to sea. "Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other risky conditions", the hurricane center said.
Hurricane Michael strengthens, Florida panhandle braces
The storm is expected to cause wide-spread power outages, high winds and heavy rain in Alabama.
Governor Scott also warned in a news conference that Hurricane Michael is a "massive storm that could bring total devastation to parts of our state, especially in the panhandle".
Farther inland, in the state capital, Tallahassee Mayor Andrew Gillum, Florida's Democratic nominee for governor, helped people fill sandbags.
The alert came as the tropical storm system strengthened to a Category 1 hurricane, packing maximum sustained winds of 120 kilometres per hour, earlier in the day.
A hurricane warning was in effect for the Alabama-Florida border to the Suwannee River, with a hurricane watch in place from the Alabama-Florida border to the Mississippi-Alabama border.
By Monday evening, lines had formed at gas stations and grocery stories as people sought emergency supplies even as the anticipated evacuations would be intensifying in coming hours.
Residents of Florida's Panhandle frantically filled sandbags, boarded up homes and secured boats in harbours Monday as they anxiously awaited Hurricane Michael, which forecasters warned could smash into the northeast Gulf Coast as a unsafe major hurricane within days.
In Alabama, the entire state was under an emergency declaration.
Michel Barnier primed for No 10's middle way on Irish border
Asked if an exit from Brexit was still possible, Mr Juncker said: "That is in the discretion of the British Parliament and the Government".