Tens of thousands of people in Florida have already lost electricity as the outer bands of Hurricane Irma batter southern parts of the state.
Governor Rick Scott said the storm surge was likely to be between six and 12 feet (two and four metres) in some areas.
“This will cover your house,” he said.
Irma was downgraded to category three on Saturday, but still has maximum sustained wind speeds of 130mph.
It is expected to strengthen again as it continues its approach towards the southern US.
The eye of the storm is predicted to hit southwest Florida and Tampa sometime on Sunday, America’s National Hurricane Centre said.
The whole state, however, is likely to feel its effects.
While Miami is not expected to get Irma’s core, the city will still experience life-threatening conditions.
Around 5.6 million Florida residents have been ordered to evacuate.
Approximately 51,000 residents have taken refuge in around 300 shelters – mostly in southeast Florida.