A hurricane ripped shingles off roofs and blew over trees as it battered the Bahamas before heading to the Florida coast.
Officials in Miami are closing beaches, marinas and parks ahead of the arrival of Hurricane Isaias.
Miami mayor Carlos Gimenez said 20 evacuation centres were on standby that could be set up with COVID-19 safety measures.
He said: “We still don’t think there is a need to open shelters for this storm, but they are ready.”
Mr Gimenez added that social-distancing measures meant each person in a shelter would need 40 square feet and there would be no cafeteria-style dining.
Florida governor Ron DeSantis said the state was “fully prepared for this and any future storm during this hurricane season”, with stockpiles of personal protective equipment, generators, bottled water and meals ready to be distributed.
But he urged people to have seven days’ of food, water and medication on hand and said state-run coronavirus testing sites in the areas where the storm could hit would be closed.
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He said: “Our sites, because they’re outdoors with tents, if it were to get 40-, 50-mile-per-hour winds, it would just collapse.”
Authorities in North Carolina ordered the evacuation of Ocracoke Island, which was slammed by last year’s Hurricane Dorian, starting on Saturday evening.
Isaias had maximum sustained winds of 85mph early Saturday and some strengthening was possible later on Saturday, the US National Hurricane Centre in Miami said.
Trevor Basden, director of the Bahamas meteorology department, told people to “continue to hunker down”.
Two islands, Abaco and Grand Bahama, were battered by Dorian, a category five storm that hovered over the area for two days and killed at least 70 people.
People are still living in tents on both islands and they have now been evacuated.
People living in the eastern end of Grand Bahama were also being moved.
Paula Miller, Mercy Corps director for the Bahamas, said that while the islands can normally withstand strong hurricanes, some have been destabilised by the coronavirus pandemic and the damage caused by Dorian.
She said: “With everything not quite shored up, property not secured, even a Category 1 will be enough to set them back.”
The country’s prime minister, Hubert Minnis, relaxed a coronavirus lockdown as a result of the storm, but imposed a 10pm to 5am curfew.
He said supermarkets, pharmacies, gas stations and hardware stores would be open as long as weather permitted.
The Bahamas has reported more than 570 confirmed COVID-19 cases and at least 14 deaths.
While still a tropical storm, Isaias toppled trees on Thursday, destroyed crops and caused widespread flooding and small landslides in the Dominican Republic and Puerto Rico, where hundreds of thousands of people were left without power and water.
Officials reported that a man died in the Dominican Republic when he was electrocuted by a fallen electrical cable.
In Puerto Rico, the national guard rescued at least 35 people from floodwaters that swept away one woman who remained missing.