Sea spray, sand and winds sweep across South Ocean Boulevard in Palm Beach, Florida, on Saturday. AP

Isais, downgraded from a hurricane but still a powerful tropical storm, churned toward Florida on Sunday, set to brush the state's east coast with strong winds and potential coastal flooding.

By 2am (0600 GMT), Tropical Storm Isaias was about 90 miles (140 km) southeast of West Palm Beach, heading northwest with top sustained winds of 70 miles per hour (110 kph), the National Hurricane Center said.

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On its current path, Isaias will move near or along Florida's east coast during Sunday, possibly strengthening, the Miami-based NHC said. On Monday and Tuesday, its center would move from offshore of the coast of Georgia into the southern mid-Atlantic states.

Florida's central and northern east coast could be hit by a storm surge - when a storm pushes normal tidal levels above normal - of as much as 4 feet (1.22 m), the NHC said.

Trees are buffeted by strong winds as Hurricane Isaias hits the Bahamas in this still image taken from a video. Reuters

Isaias was not expected to affect the return home on Sunday of two NASA astronauts who rode to the International Space Station aboard SpaceX's new Crew Dragon.

They were heading for a splashdown in the Gulf of Mexico, off Florida's northwest coast, capping a two-month voyage in space that marked NASA's first crewed mission from home soil in nine years.

Florida is used to being hit by hurricanes, but its well-honed storm responses have been partly upended by its grappling with one of the country's worst coronavirus outbreaks.

The state has recorded more than 480,000 cases, with tens of thousands recorded in the last week alone, according to a Reuters tally.

Residents work to cover a second-floor window in downtown Fort Pierce, Florida, on Saturday. AP

The emergency operations center in Miami was mostly empty on Saturday with plastic dividers set up between work stations and fans with ultraviolet lights hung around the room. Many emergency officials are instead working remotely.

Governor Ron DeSantis said on Saturday the state emergency management division was supplying shelters with enough personal protective equipment for 10,000 people.

DeSantis declared a state of emergency for a dozen counties on the Atlantic coast, which makes it easier to mobilize resources. North Carolina Governor Roy Cooper followed suit.

The storm has caused at least two deaths in the Dominican Republic and torn down trees, flooded streets and knocked out power for thousands of homes and businesses in Puerto Rico, according to media reports.

Reuters