The storm made landfall as a powerful Category 4, the second highest rating on the Saffir-Sampson wind scale, and strike a stretch of the state's north-western coastline known as the Florida Panhandle.
As it came ashore, Michael was just shy of a Category 5 - defined as a storm packing wind speeds of 250km/h or above.
Rick Reichmuth, Fox News' chief meteorologist, said Michael was the fourth most powerful storm to ever make landfall in the U.S.in terms of wind, and the third most powerful in terms of pressure, at 919 mb.
Michael benefited from deep pockets of warm water in the Gulf, which meant that even as the storm stirred the water it crossed, it wasn't churning up cool water that could sap its strength, said Bryan Norcross, a hurricane specialist with WPLG, a TV station in South Florida.
Forecasters said it would unleash damaging wind and rain all the way into the Carolinas, which are still recovering from Hurricane Florence's epic flooding.
"Along our coast, communities are going to see unimaginable devastation", Scott said, with storm surge posing the greatest danger.
"That's what happened with Hurricane Andrew - [the National Hurricane Center] looked at the pressure and reanalyzed and upgraded it to a Category 5 storm. We can rebuild your house, but we cannot rebuild your life", Scott said at a press conference Tuesday, warning that "this storm can kill you". "As this thing pushes through, you're going to see a lot of inland wind damage, you're going to see a lot of power outages for multiple weeks".
"My God, it's scary. I didn't expect all this", said Bill Manning, 63, a grocery clerk who left his camper van in Panama City to move into a hotel where the power eventually went out.
More than 17,000 people tuned into the broadcast, including Sen.
By Wednesday night, more than 403,000 homes and businesses were without electricity in Florida, Georgia and Alabama, utility companies said.
"We are catching some hell" was how a Panama City Beach resident who chose to ride it out described Michael as it made landfall.
Patterson said about 2,500 of the town's 3,500 people were still there, including about 100 in a beachside area who ignored a mandatory evacuation order.
Michael is the lowest pressure hurricane to strike the USA mainland since 1969.
Damage in Panama City was so extensive that broken and uprooted trees and downed power lines lay almost everywhere.
Speaking in the Oval Office Donald Trump said: "This started off very innocently a week ago, a small storm".
Trees and wires are down throughout Florida Gulf Coast towns.
Based on wind speed, Michael is the fourth-strongest USA -landfalling hurricane, behind Andrew, Camille in 1969, and the biggest one of all, an unnamed 1935 Labor Day storm that had winds of 184 miles per hour.