Forecasters predict winds could top 110mph by Tuesday night as it heads past Cuba and Mexico towards the US.
Hurricane Michael, pictured in a satellite image taken on October 8, 2018, when it was still a tropical storm, could produce life-threatening flooding.
With the storm next entering the eastern part of the Gulf of Mexico, which has warm water and favorable atmospheric conditions, "there is a real possibility that Michael will strengthen to a major hurricane before landfall, " Robbie Berg, a hurricane specialist at the Miami-based storm forecasting hub, wrote in an advisory. He said he could see broken street signs and a 90-foot pine bent at a 45-degree angle.
The storm is now moving north, crossing into the Gulf of Mexico, and will likely curve to the east after its coastal impact. They can cause catastrophic damage and flooding, toppling houses and destroying roads.
At 11 a.m. ET (1500 GMT) on Tuesday, Michael's center was about 335 miles (535 km) south-southwest of Apalachicola, Florida, heading north at around 12 mph (19 kph), the NHC said.
"Today is the day". It developed into a hurricane on Monday, and by Tuesday, more than 180,000 people were under mandatory evacuation orders.
Florida Panhandle's Escambia County Sheriff David Morgan issued a chilling warning to residents who choose to ride out the storm at home.
Tropical storm warnings were issued for the coasts of Mississippi, Alabama and Florida.
More than 300 miles of coastline from Mobile, AL, through the Florida Panhandle and Big Bend area are threatened, according to the NHC. Forecasters said rainfall could reach up to a foot (30 centimeters), and the life-threatening storm surge could swell to 14 feet (4 meters). Damaging winds will also extend inland across portions of the Florida Panhandle, southern Georgia, and southeast Alabama as Michael moves inland.
Florida Governor Rick Scott urges residents to obey evacuation orders as Hurricane Michael strengthens to a Category 2 storm.
President Donald Trump approved a pre-landfall emergency declaration to provide federal money and help in Florida.
Michael is expected to be the strongest hurricane, based on wind speeds, to make landfall in the continental U.S. since Irma in September of previous year. "It looks like another big one".
Here are some other facts that show the power of this "monstrous storm".
The "forecast cone" for Michael (the storm's projected path) stretches from Florida all the way north to New Jersey.
The NHC says some coastal regions can expect 9 to 13 feet of storm surge, as the hurricane's winds drive a wall of water onto the low-lying shore.
The storm should continue on its current direction until Wednesday, when it is expected to turn northeast and go ashore just east of Panama City. 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.