Michael is now about 90 miles south of Cozumel, Mexico.
The heavy winds and rain - which are heading out near Honduras in the Northwestern Caribbean Sea- are expected to reach the Gulf by Monday, forecasters said.
"Heavy rainfall from Michael could produce life-threatening flash flooding from the Florida Panhandle and Big Bend region into portions of the Carolinas through Thursday", the hurricane center said.
It's a on track expected to move over the eastern Gulf of Mexico late Monday through Tuesday night and approach the northeast U.S. Gulf Coast on Wednesday.
By Monday morning, almost the entire central US will see very heavy rain and possible strong storms.
"Remember this storm could grow stronger and be a Category 3 hitting our state", Scott said, noting that winds could pick up to more than 100 miles per hour by midweek.
"This storm will be life-threatening and extremely risky", said Scott, who also warned of hurricane-driven storm surge that could affect most of the state: "If this storm hits Panama City, Tampa could still have storm surge".
"With the National Hurricane Center forecasting Tropical Depression 14 to strengthen and impact Floridas Panhandle as a hurricane, families need to get prepared", the governor said in a release. It is forecast to strengthen into a hurricane by Monday night or Tuesday as its center moves over the Yucatan Channel, crosses the Gulf of Mexico and nears the Florida Panhandle coast sometime Wednesday.
Scott also announced that he was activating 500 members of the Florida National Guard to assist with planning, logistics and storm response. The storm is now a Category 4 on the Saffir-Simpson scale which measures hurricane intensity, with 1 being the weakest and 5 the strongest. The Hurricane Center's statement said interests along the northeastern and central U.S. Gulf Coast should monitor the progress of the depression.
The storm was about 90 miles (145 kilometers) south of Cozumel, Mexico by mid-day Sunday.
Tropical storm warnings are in effect for Mexico's Yucatan Peninsula, including Cancun, and western Cuba, where tropical storm conditions will develop overnight.
The 2018 Atlantic Hurricane Season is far from over - and the USA will likely see yet another land-falling tropical system in the coming week.