Governor Rick Scott’s office said mandatory evacuation orders were in place for parts of Bay County, which includes the popular Panama City beach resort, and areas in nearby Gulf and Franklin counties.
“EVERY FAMILY must be prepared. We can rebuild your home, but we cannot rebuild your life,” Scott said.
The alert came after the tropical storm system strengthened to a Category 1 hurricane, packing maximum sustained winds late Monday of 85 miles (140 kilometers) per hour, the Miami-based National Hurricane Center (NHC) said.
Michael was forecast to have the power to uproot trees, block roads and knock out power for days by the time it hits Florida on Wednesday. Then it is forecast to lash the southeastern United States through Thursday.
Earlier it said Michael could produce three life-threatening hazards along portions of the northeastern Gulf Coast: storm surge, heavy rainfall, and hurricane-force winds, with storm surge and hurricane watches in effect.
The first rains from Michael already started to soak the Florida Keys on Monday. Up to four inches (10 centimeters) were expected to fall through Tuesday.
Late Monday, residents of far western Cuba were forecast to get up to eight inches of rain.
“This rainfall could lead to life-threatening flash floods and mudslides,” the NHC warned.
Scott declared a state of emergency for 35 counties, activating 1,250 National Guard troops in preparation for the storm.
Florida State University announced it was closing for the week on Tuesday, along with schools in Leon County, home to the state capital Tallahassee.
The Carolinas are still recovering from Hurricane Florence, which left dozens dead and is estimated to have caused billions of dollars in damage last month.
It made landfall on the coast as a Category 1 hurricane on September 14 and drenched some parts of the state with 40 inches of rain.
Last year saw a string of catastrophic storms batter the western Atlantic — including Irma, Maria and Hurricane Harvey — causing a record-equaling $125 billion in damage when it flooded the Houston metropolitan area.