Anxious meteorologists said it had the potential to become one of the worst storms in the history of Florida's Panhandle. It's expected to cause life-threatening flash floods and send surges of ocean water into coastal areas along the Gulf, from Pensacola around the coast to Tampa.
Michael, which increased to a Category 1 hurricane midday Monday, will rapidly intensify over the next 24 to 36 hours, Orrock said.
The neighbouring states of Alabama and Georgia have also declared a state of emergency.
"Today is the day". Michael is now centered about 360 miles south of Panama City, Florida, and landfall is likely to occur sometime around midday Wednesday between the Florida Panhandle and the state's Big Bend.
Michael could dump up to 30 centimetres 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. Weakening is expected after landfall as Michael moves across the southeastern United States.
President Trump has approved Florida's declaration of emergency.
Hurricane Michael has grown stronger tonight and is now up to category four status with winds at.
About 2,500 National Guard troops were deployed to assist with evacuations and storm preparations, and more than 4,000 others were on standby.
Though Michael has a fierce core of winds around its eye, one of the biggest concerns with its eventual landfall is the storm surge likely to come in points east of wherever the hurricane's eye makes landfall.
On the exposed coast of Florida's Big Bend, most of the waterfront homes in Keaton Beach stood vacant amid fears of a life-threatening storm surge in an area that hadn't seen a potentially catastrophic major hurricane in decades. But the surging seawater could also create perilous problems far from the coast, raising rivers and bays to risky levels as it pushes as much as 10 to 15 miles inland.
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"In comparison, AccuWeather's final damage and economic impact prediction of $60 billion (£52,479,000,000) for Florence was largely due to the storm's inland flooding and damage".
"The good news is, if anything, it'll be moving so quickly that by the time it gets up to mid-latitudes in the Carolinas or Virginia, it's going to get in and out of here really fast", Orrock said. The governor has declared a state of emergency in 35 counties and is stressing that residents should "absolutely" evacuate if ordered to.
Forecasters said some regions of the U.S. may see 30cm of rain, and storm surges of up to 3.6m. More than 80 deaths were linked to that storm, according to The Associated Press - including residents of a nursing home.
After it makes landfall, the storm is predicted to pass into Georgia, where Gov. Nathan Deal on Tuesday issued a state of emergency covering 92 counties - almost the entire lower two-thirds of his state.
Rick Knabb, a former NHC head, urged locals in Michael's path to waste no time in evacuating.
Peaton says he is working closely with the National Weather Service to provide accurate information and protective measures to his county, which faces the Gulf of Mexico and is especially vulnerable to any flooding produced by Michael.
Annette Strickland, 75, arrived at a Tallahassee high school.
Both Peaton and Scott encourage residents to have at least three days' worth of food and supplies and to check on their neighbors and monitor local news coverage.
"Hurricane Michael is a monster storm and it keeps getting more risky".
The last NHC report said the fast-moving storm was about 180 miles (325 km) from Panama City, Florida.
With Hurricane Michael's landfall on the Gulf Coast expected on Wednesday, officials in coastal counties were preparing for evacuations and emergencies.