But heavy rain could trigger "life-threatening flash floods" in the Florida Panhandle, southeastern Alabama, Georgia, the Carolinas, and southern Virginia as the storm moves to the northeast, according to the National Hurricane Center.
Florida Gov. Rick Scott described it as a "monstrous storm" and urged people to get out of the way.
This will be the third storm to hit Northwest Florida this year.
Along with the mandatory evacuation orders come a notably tighter security. That put it just shy of a Category 5 hurricane, which would require wind speeds of 157 miles per hour, but Michael is nevertheless one of the strongest storms to ever strike the American mainland.
As of late afternoon, the storm's winds had dropped to Category 3 strength at 125 miles per hour and was moving north-northeast at 16 miles per hour.
Even before Hurricane Michael made full landfall - which is the point where the eye of the storm hits land - it was knocking down trees with powerful winds and had caused flooding in the town of Apalachicola and Port St Joe, where more than 1.5 metres of water was reported.
Pensacola Mayor Ashton Hayward on preparations ahead of Hurricane Michael.
Michael's pressure was 919 millibars as of 1:00 p.m. ET, making it more powerful than Hurricanes Katrina or Andrew.
This map shows the probable path of Hurricane Michael which made landfall Wednesday.
The hurricane was set to make landfall later on Wednesday on Florida's Panhandle and could drive sea water levels as high as 14 feet above normal in some areas, the center said.
Warning Coordination Meteorologist Nick Petro with the National Weather Service Office in Raleigh says Michael will be a wind and rain event locally, with the possibility for gusty winds and 3-5 inches of rainfall. Several dozen people were killed in the storm, which also ended a catastrophic drought in the region.
Where the military ends up responding could shift north as Michael moves up the coast to the Carolinas, which are still recovering from Hurricane Florence. Wind shear is when there's a mismatch either in speed or direction between winds near the surface and those five to six miles (8 to 10 kilometers) up. While the latest storm isn't expected to dump as much rain on the Palmetto State as its predecessor, winds are expected to be stronger in some areas. Heavy rainfall will drench Florida's Panhandle, Alabama, Georgia and SC; up to 12 inches is possible in isolated locations.
"We expect Michael to intensify right up to landfall", he said.
The storm's center is now on track to make landfall "pretty close to Panama City" early Wednesday afternoon, Graham said. Total rainfall for most of the area will be between 3 to 4 inches with isolated higher amounts.