Updated at 5:10 a.m. ET Thursday
Hurricane Dorian is "expected to become a major hurricane on Friday," according to the National Hurricane Center.
Maximum sustained winds at 5 a.m. ET Thursday were 85 mph — a Category 1 hurricane — with higher gusts, according to the center's most recent update. Dorian was about 150 miles north northwest of Puerto Rico, moving about 13 mph toward the northwest.
Dorian's sustained winds topped 80 mph, hitting Puerto Rico and St. Thomas in the Virgin Islands before heading northwest. Forecasters are now warning that the storm will strengthen into a dangerous Category 3 hurricane, defined as sustained winds of at least 111 mph.
"Heavy rains are expected to occur over portions of the Bahamas, Florida, and elsewhere in the Southeastern United States later this week and into early next week," forecasters said.
"All indications are that by this Labor Day weekend, a powerful hurricane will be near or over the Florida peninsula," the National Hurricane Center said at 5 a.m. ET.
Florida Gov. Ron DeSantis has declared a state of emergency for 26 counties in the possible path of the hurricane.
"The Hurricane Warning for Vieques, Culebra, and the U.S. Virgin Islands has been discontinued," the National Hurricane Center report said earlier. "The Hurricane Watch and Tropical Storm Warning for Puerto Rico have been discontinued."
Dorian caused only limited damage in Puerto Rico and the U.S. Virgin Islands.
"We're happy because there are no damages to report," Culebra Mayor William Solís told The Associated Press. He said only one community on his island lost power.
Current predictions show Dorian's center hitting Florida's coast late Sunday/early Monday.
The hurricane center has said it's too early to give an exact location where the eye will come ashore, and everyone in the affected area should make emergency preparations.
The NHC said the northern Bahamas and coastal sections of the Southeast United States could see 4 to 8 inches of rain, with 10 inches possible in isolated areas. "This rainfall may cause life-threatening flash floods," it said.
NHC Director Ken Graham cautioned that anyone on the Southeastern U.S. coast from Florida up through Georgia and South Carolina should watch for potential hazards.
Earlier, President Trump had declared an emergency in the commonwealth of Puerto Rico, ordering the Federal Emergency Management Agency late Tuesday to provide "equipment and resources necessary to alleviate the impacts of the emergency."
Puerto Rico Gov. Wanda Vázquez Garced thanked Trump for approving the declaration, saying it would "allow federal aid to arrive more quickly" after the storm passes.
Trump approved an emergency declaration for the Virgin Islands on Wednesday.
In a statement about its preparations, FEMA said that its "stock on the island compared to 2017 levels includes three times as many generators, nine times as many meals, five times as many liters of water and 16 times as many blue tarps."
Meanwhile, the fifth named storm of the 2019 Atlantic season formed late Tuesday, as Tropical Storm Erin's winds reached 40 mph. The storm, which was several hundred miles southeast of Cape Hatteras, N.C., was downgraded to a tropical depression on Wednesday. Erin is expected to remain on a north-northeastern track, likely arriving at Canada's coast late this week.
NPR's Windsor Johnston contributed to this report.