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.
Two people, including a child, were killed by falling trees, officials say. Another 40,000 were without power in Georgia and 41,000 in Alabama.
Hurricane Michael continues to gain strength as it moves through the southern Gulf of Mexico.
The second possible outcome is that the storm could cause inland flooding and push the red tide into fertilized zones, supplying the red tide bacteria with a buffet and allowing to procreate even more, AccuWeather reported. Local authorities fear power outages and major tree damage from Michael.
Residents of Florida Panhandle to central Georgia in the US have heaved a sigh of relieve as Hurricane Michael downgraded early Thursday to a tropical storm after leaving a trail of destruction including at least two deaths.
Its rapid intensification caught many by surprise, although the storm later weakened. But fears lingered that some failed to heed the calls to get out of Michael's way as the hard-charging storm began speeding north over the warm waters of the Gulf of Mexico.
President Donald Trump told reporters on Tuesday: "We are very well prepared for the incoming hurricane".
The governors of North and SC urged residents to brace for more heavy rain and storm-force winds as Michael plows northward up the Atlantic seaboard.
"We are in new territory", National Hurricane Center Meteorologist Dennis Feltgen wrote on Facebook.More news: Markets hammered after USA stocks rout
"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 the shore of Apalachicola Bay, which where about 90 percent of Florida's oysters are harvested. After it ravaged the Panhandle, Michael entered south Georgia as a Category 3 hurricane - the most powerful in recorded history for that part of the neighbouring state.
Michael is likely to cause flooding and a storm surge along the coast.
The National Hurricane Center in Miami says the hurricane was 395 miles (635 kilometers) south of Panama City, Florida, and 365 miles (590 kilometers) south of Apalachicola, Florida.
Top winds: 155 miles per hour (250 kph), strong enough to completely destroy homes and cause weekslong power outages. "And if not, that they're not in those structures". Forecasters expect Michael will be followed by the first true taste of fall weather in North Carolina this year, with sunny skies and high temperatures in the low 70s both Saturday and Sunday.
Schools and state offices in the area are to remain shut this week.
Scott said the state is working with the American Red Cross and National Guard to assist counties with shelter needs.
The Atmospheric Infrared Sounder or AIRS instrument aboard NASA's Aqua satellite passed over Hurricane Michael on October 8 at 2:47 p.m. EDT (1847 UTC) just after it strengthened into a Category 1 hurricane and analyzed the storm in infrared light. A Tropical Storm Watch is in effect for Chassahowitzka to Anna Maria Island Florida, including Tampa Bay, the Mississippi/Alabama border to the Mouth of the Pearl River and from Fernandina Beach, Florida to South Santee River, South Carolina.
"Michael is forecast to re-strengthen some Thursday night and Friday when it moves off the east coast of the United States and becomes a post-tropical cyclone on Friday", the NHC added.