"On the forecast track, the center of Michael will move across the eastern Gulf of Mexico through tonight", the agency said.
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.
Tropical Storm Michael has turned into a hurricane and is expected to strengthen rapidly before hitting Florida this week, bringing with it winds of at least 160 kilometres per hour and life-threatening flash flooding.
A Hurricane Warning is in effect from the Alabama/Florida border to Suwannee River, Florida.
Governor Scott warned in a news conference that Hurricane Michael was a "massive storm that could bring total devastation to parts of our state, especially in the panhandle".
Unlike Florence, which ravaged the eastern Carolinas only three weeks ago, Michael is expected to move rapidly once it bores inland to Georgia and SC.
Forecasters advised residents along the northeastern and central US Gulf Coast to monitor the storm's progress.
Wind shear will remain the only deterrent to the strength of Michael prior to landfal.
The Coming Kavanaugh Court Doctrine: Democrats Are Unconstitutional
He was voted in by 50 votes to 48, handing Donald Trump a huge victory ahead of the midterms in November. Trump ordered the probe, but later complained that Senate Democrats were just trying to waste time.
Peyton Manning jokingly shames Drew Brees for breaking his passing record
Behind three touchdowns from Brees, New Orleans cruised to a 43-19 win over the Washington Redskins . Drew Brees knocked Peyton Manning into second place on the NFL's all-time passing leaderboard.
Weird light in Arizona sky is from SpaceX launch
In the launch, scheduled for shortly after 7:20 p.m., a Falcon 9 rocket will carry the satellite SAOCOM 1A to space. SpaceX has flown boosters back to land after launches from Florida but has yet to do so in California.
"Guess what? That's today", National Hurricane Center Director Ken Graham said.
With an officiant standing in front of them, the couple said their vows on the beach as brisk winds brushed them.
Hurricane Michael is growing stronger, expected to make landfall on Wednesday as a Category 3 hurricane. But Michael will also have implications further away. Many filled sandbags and boarded up homes.
The sheriff's office says Wakulla County shelters were rated safe only for hurricanes below that threshold.
Scott declared a state of emergency in 35 counties along the Panhandle and Florida's Big Bend regions, mostly rural areas known for small tourist cities, beaches and wildlife reserves, and the state capital, Tallahassee. Heavy rain, storm surge, and downed trees and power lines are also expected along Florida's western coast.
Hurricane Michael is poised to slam Florida's Panhandle by Wednesday afternoon, threatening unsafe storm surges to low-lying areas ill-equipped to handle them - and officials are urging people to get out of the way now.
With a number of counties ordering evacuations, Scott waived highway tolls in the northwest part of the state. "We're going to get storm surge, we have wind, we have a chance of flooding, we have a significant chance of tornadoes".
The advisory shows Michael has grown from a Category 2 storm into a Category 3 storm as it heads for the Florida Panhandle, where it's expected to make landfall sometime Wednesday.
In Alabama, the entire state was under an emergency declaration.
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.