Parts of Florida, Georgia and SC could see "life-threatening flash flooding" as a result of the rain, according to a tweet from the National Weather Service.
A hurricane hunter plane that bounced into the swirling eye off the western tip of Cuba found wind speeds rising.
More than 20 million people are under a hurricane watch or warning across five states (Florida, Alabama, Mississippi, Georgia, South Carolina).
Mr Scott said people in areas that could be affected should take no chances against such a powerful surge, adding: "No one's going to survive such a wall of water".
"I'm asking all Floridians to stay vigilant throughout tonight and tomorrow as we brace for Hurricane Michael to make landfall".
Scott said his main concern from the rapidly developing hurricane is storm surge, which the National Weather Service estimates could reach eight to 12 feet between Indian Pass in Gulf County and Cedar Key in Levy County and top six feet from Crystal River in Citrus County to the Okaloosa-Walton County Line.
Forecasters said it could bring 3 to 6 inches of rain to Georgia, the Carolinas, and Virginia, triggering flash flooding in a corner of the country still recovering from Hurricane Florence.
United Way of the Chattahoochee Valley also said that anyone seeking local resources connected to Hurricane Michael can dial 2-1-1 or 706-405-4775 around the clock. Most of the rain was blamed on a low-pressure system off the Pacific coast, but Michael in the Caribbean could have also contributed.
The governor also told Florida hospitals and nursing homes to do all they can to assure the safety of the frail and elderly.
Florida Gov. Rick Scott warned that the "monstrous hurricane" was just hours away, and his Democratic opponent for the Senate, Sen.
Previous year saw a string of catastrophic storms batter the western Atlantic - including Irma, Maria and Hurricane Harvey - causing a record-equalling $125 billion in damage when it flooded the Houston metropolitan area.
"If you're responsible for a patient, you're responsible for the patient".
Bottomline - Petro says Eastern and Central Carolina need to take Hurricane Michael seriously. Many filled sandbags, boarded up homes and lined up to buy gas and groceries.
"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. The storm was moving northeast at 20 miles per hour with 75 miles per hour maximum sustained winds, just above the minimum speed to be considered a hurricane.
Officials urged residents in Michael's projected path to evacuate before it's too late - or risk being cut off from rescue.
Secretary of State Ken Detzner announced an extension Tuesday morning that will allow county supervisors to accept paper voter-registration applications when they reopen from the storm.
Tallahassee Mayor Andrew Gillum helped residents in Florida's capital fill sandbags as the monster storm loomed.
"I think that hopefully we'll get lucky, but maybe that won't happen", Trump said.
Fineout reported from Tallahassee, Florida.