Michael is expected to be the strongest hurricane, based on wind speeds, to make landfall in the continental USA since Irma in September of previous year.
The communities along the Panhandle coast can be hard to reach, with two-lane roads connecting several towns, and bridges that have never experienced the powerful winds Michael promises to pack.
Gov. Rick Scott and state emergency officials were already gearing up for a lengthy recovery process, anticipating days of power outages and promising extensive efforts to rescue those who didn't evacuate and get food and water to those in need.
Michael is forecast to lash coastal areas of Florida, Alabama and Georgia with as much as 12 inches of rain.
NHC Director Ken Graham said Michael represented a "textbook case" of a hurricane system growing stronger as it drew near shore, in contrast to Hurricane Florence, which struck North Carolina last month after weakening in a slow, halting approach.
The storm will quickly move inland and race to the northeast through the Southeastern US, exiting the Mid-Atlantic and sliding south of New England before the weekend.
Separately, the National Weather Service in the state capital Tallahassee issued a dramatic appeal for people to comply with evacuation orders. Scott on Monday also declared a state of emergency in 35 Florida counties.
"Storm surge is the No. 1 problem that you can see from these storms".
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Michael's eye was about 140 miles (225 kilometers) from Panama City and 130 miles (209 kilometers) from Apalachicola, but moving relatively fast at 13 mph (21 kph).
Top sustained winds were reported to be near 140 miles per hour at 5am.
President Donald Trump, who was in Orlando delivering an address to a global association of police chiefs, said the federal government was ready and urged residents to be prepared for the worst.
Michael could cause as many as 1.8 million customers to lose power across the Florida Panhandle and southern Georgia, according to a computer model run by the Guikema Research Group at the University of MI. There are specific protocols to its possible closure: Panama City Mayor Greg Brudnicki told CNN on Tuesday that officials will close the bridge when winds reach 50 miles per hour and stay that strong for longer than two minutes.
A storm surge warning is in effect from the Okaloosa-Walton County line to the Anclote River in Florida.
"That means the water will come miles inshore and could easily be over the roofs of houses", Scott said. Airbnb is offering free shelter to evacuees in some parts of Florida, Georgia and Alabama.
"The last thing we need is more water", said Carolyn Causey, business manager of the Trinity United Methodist Church in Conway, South Carolina.
Meanwhile, tropical storm watches were in effect in some coastal areas of Mississippi, Florida, Georgia, and SC.
"We're looking at a significant storm with significant impact, possibly greater than I've seen in my 59 years of life", Johnson said of his city on Apalachicola Bay, where about 90 percent of Florida's oysters are harvested.