Drawing energy from warm waters of the Gulf of Mexico, the storm strengthened rapidly into a potentially devastating Category 3 during the day and just kept getting stronger in the hours ahead of an expected Wednesday landfall. Forecasters said Michael was expected to strengthen further overnight and become a Category 4 brute before slamming ashore.
The core of the storm was expected to crash ashore around midday Wednesday near Panama City Beach, along a lightly populated stretch of fishing villages and white-sand spring-break beaches.
Florida officials said that roughly 375,000 people have been urged or ordered to evacuate. Those evacuations stretched across 22 counties from the Florida Panhandle down into north central Florida. But there were fears, however, that some people weren't heeding the calls to get out despite predictions of a life-threatening storm surge.
Franklin County Sheriff A.J. Smith said his deputies had gone door to door in some places along the coast to urge people to evacuate. "We have done everything we can as far as getting the word out," Smith said. "Hopefully more people will leave."
While Florence took five days between the time it turned into a hurricane and the moment it rolled into the Carolinas, Michael gave Florida what amounted to two days' notice. It developed into a hurricane on Monday, and by Tuesday, more than 180,000 people were already under mandatory evacuation orders.
"We don't know if it's going to wipe out our house or not," Jason McDonald, of Panama City, said as he and his wife drove north into Alabama with their two children, ages 5 and 7. "We want to get them out of the way."
At 11 p.m. EDT, the eye of Michael was about 220 miles (355 kilometers) south-southwest of Panama City, Florida. It also was about 200 miles (325 kilometers) south-southwest of Apalachicola, Florida. But forecasters said its winds and outer rainbands would begin to start lashing the coast hours ahead of the eye.
Florida Gov. Rick Scott warned it was a "monstrous hurricane," and his Democratic opponent for the Senate, Sen. Bill Nelson, said a "wall of water" could cause destruction along the Panhandle.
"Don't think that you can ride this out if you're in a low-lying area," Nelson said on CNN.
But some officials were worried by what they weren't seeing - a rush of evacuees.
"I am not seeing the level of traffic on the roadways that I would expect when we've called for the evacuation of 75 percent of this county," Bay County Sheriff Tommy Ford said.
Aja Kemp, 36, planned to stay in her mobile home in Crawfordville. She worked all night stocking shelves at a big-box store that was closing later Tuesday, then got to work securing her yard.
Kemp said the bill totaled over $800 when she and her family fled Hurricane Irma's uncertain path last year.
"I just can't bring myself to spend that much money," she said. "We've got supplies to last us a week. Plenty of water. I made sure we've got clean clothes. We got everything tied down."
In the dangerously exposed coastal town of Apalachicola, population 2,500, Sally Crown planned to go home and hunker down with her two dogs.
"We've been through this before," she said. "This might be really bad and serious. But in my experience, it's always blown way out of proportion."
Mandatory evacuation orders went into effect in Panama City Beach and other low-lying areas in the storm's path. That included Pensacola Beach but not in Pensacola itself, a city of about 54,000.
Forecasters said parts of the Panhandle and Florida's marshy, lightly populated Big Bend area - the crook of Florida's elbow - could see 9 to 13 feet (2.7 to 4 meters) of storm surge.
About 20 miles (32 kilometers) in from the coast, in Tallahassee, the state capital, people rushed to fill their gas tanks and grab supplies. Many gas stations in Tallahassee had run out of fuel, including the Quick 'N' Save, which was also stripped clean of bottled water and down to about two dozen bags of ice.
Tallahassee Mayor Andrew Gillum, Florida's Democratic nominee for governor, helped people fill sandbags.
Several people were taken by van from coastal Wakulla County to Tallahassee's Leon County to the north. Wakulla County's shelters are not considered reliable against storms stronger than a Category 2.
Michael could dump up to a foot (30 centimeters) of rain over some Panhandle communities before its remnants go back out to sea by way of the mid-Atlantic states over the next few days.
Forecasters said it could bring 3 to 6 inches (7 to 14 centimeters) of rain to Georgia, the Carolinas and Virginia, triggering flash flooding in a corner of the country still recovering from Florence.
"I know people are fatigued from Florence, but don't let this storm catch you with your guard down," North Carolina Gov. Roy Cooper said, adding, "A number of homes have rooftop tarps that could be damaged or blown away with this wind."
While Florence wrung itself out for days and brought ruinous rains, fast-moving Michael is likely to be more about wind and storm surge.
As the storm closed in on the U.S., it caused havoc in the Caribbean.
In Cuba, it dropped more than 10 inches (27 centimeters) of rain in places, flooding fields, damaging roads, knocking out power and destroying some homes in the western province of Pinar del Rio. Cuban authorities said they evacuated about 400 people from low-lying areas.
Disaster agencies in El Salvador, Honduras and Nicaragua reported 13 deaths as roofs collapsed and residents were carried away by swollen rivers.
Lush reported from St. Petersburg, Fla. Associated Press writers Jonathan Drew in Raleigh, N.C., and Jay Reeves in Troy, Alabama, contributed to this report.
Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.