Isaias weakened from a hurricane to a tropical storm Saturday after it blew through the Bahamas, but the storm is expected to regain its hurricane strength as it passes over warm water overnight on its way to Florida.
Isaias was moving northwest with maximum sustained winds of 110 kph (70 mph), the U.S. National Hurricane Center said Saturday afternoon. It was expected to reach the southeastern coast of Florida early Sunday and travel up the state's east coast toward North Carolina.
Both Southern U.S. states of Florida and North Carolina declared hurricane warnings.
Florida Governor Ron DeSantis declared a state of emergency for a dozen counties on the Atlantic Coast. Heavy rains from the storm were expected to begin in Florida on Saturday and arrive over the Carolinas by early next week.
"The most important thing we want people to do now is remain vigilant," DeSantis said.
Florida is one of the U.S. states hit hardest by the coronavirus, with more than 470,000 infections and more than 6,800 deaths as of Saturday, according to Johns Hopkins University.
The storm prompted authorities in parts of Florida to close COVID-19 testing sites at a time when cases have been growing in the state.
Officials in Miami-Dade County said they did not believe it would be necessary to open evacuation centers for this storm but said 20 centers remained on standby in case conditions changed.
In North Carolina, in addition to declaring emergencies in coastal counties, Governor Roy Cooper also ordered the evacuation of Ocracoke Island, which was hit by last year's Hurricane Dorian.
In the Bahamas, Isaias downed trees and knocked out power. Officials evacuated people in Abaco and in the eastern end of Grand Bahama.
Isaias is the ninth named storm of a busy Atlantic hurricane season. This is the earliest date a storm beginning with the letter "I" has formed.