Updated at 5:42 p.m. ET

Tropical Storm Dorian officially became Hurricane Dorian on Wednesday, its sustained winds topping 80 mph with higher gusts as it passed over Puerto Rico and St. Thomas in the Virgin Islands. Forecasters are now warning that the storm will strengthen into a dangerous Category 3 hurricane as it nears the U.S. mainland.

"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 in its 5 p.m. ET report.

Florida Gov. Ron DeSantis has declareda state of emergency for 26 counties in the path of the hurricane.

The apparent eye of Hurricane Dorian was located about 45 miles northwest of St. Thomas as of Wednesday evening.

"Hurricane conditions are ongoing over portions of the U.S. Virgin Islands, and could still occur over Vieques, Culebra, and the British Virgin Islands during the next several hours. These winds should subside tonight. Tropical storm conditions are expected in Puerto Rico this afternoon and tonight," the National Hurricane Center said in its 5 p.m. ET update. The storm is moving northwest at around 14 mph.

Dorian is expected to become a major hurricane (Category 3 and above) as it moves north of the Bahamas. The NHC's current predictions show Dorian's center hitting Florida's coast early Monday. But the Florida coast could see tropical-storm-force winds arrive as early as Saturday night.

The center currently predicts the storm will make landfall near an area that's roughly level with Orlando. But that potential location could shift drastically as the storm develops.

As meteorologist Philip Klotzbach notes, "The average date for the 1st Atlantic major hurricane is September 3."

Forecasters warn of the potential for life-threatening flash floods in the storm's path. Southern and eastern portions of Puerto Rico and the Virgin Islands could see 4-6 inches of rainfall, with 10 inches possible in isolated areas. When the storm reaches Florida, it's expected to drop 4-8 inches of rain, with 10 inches in some spots.

Virgin Islands Gov. Albert Bryan Jr. announced Wednesday that all schools and government offices would be closed throughout the territory because of the storm. The government also spent several hours this morning distributing sandbags to residents. And as Dorian loomed, Bryan also instituted a public curfew from noon to 6 a.m. Thursday.

As Puerto Rico prepared for the storm, Gov. Wanda Vázquez Garced ordered a freeze on prices to prevent gouging; as the storm neared, she also signed a 24-hour la Ley Seca or "dry law," prohibiting alcohol sales. Saying the island had learned lessons from Hurricane Maria's devastating arrival in September 2017, Vázquez Garced said government agencies are better prepared to cope with an emergency.

Puerto Rico's public security agency says there are currently 56 shelters open to people who need help.

NHC Director Ken Graham cautioned that for Florida, even though Dorian is estimated to make landfall as of 8 a.m. ET Monday, "the impacts could come a lot earlier than that," saying intense rain, tropical-storm-force winds and a storm surge could begin to affect the coastline far from the storm's center.

Acknowledging that considerable uncertainty remains over the path Dorian will take, Graham also said anyone on the southeastern U.S. coast from Florida up through Georgia and South Carolina should watch for potential hazards.

"Dorian remains a compact and asymmetric tropical storm," the NHC says, citing data collected from Air Force Hurricane Hunters and other sources. But that could change — the center says some projection models show Dorian "increasing in size by the time it nears the southeast U.S."

While Dorian's wind speeds and size remained fairly stable earlier this week, the hurricane center is now projecting tropical-storm-force winds outward up to 80 miles from the center — up from 45 miles on Monday and Tuesday. Its hurricane-force winds extend up to 20 miles from the storm's center.

As it announced an increased threat of hurricane conditions on Florida's east coast, the hurricane center noted early Wednesday that forecasts are "on the lower end of the guidance envelope" — meaning it could raise more dire warnings as the storm continues to develop.

By 9:30 a.m. ET, Dorian's outer bands were beginning to move over eastern Puerto Rico, according to the National Weather Service office in San Juan.

To prepare for rough conditions at sea, the Coast Guard captain in San Juan set "Port Condition ZULU" Wednesday for all ports in the U.S. Virgin Islands and Puerto Rico, shutting down all commercial traffic until the storm has passed and the facilities have been assessed.

President Trump 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."

Vázquez Garced thanked Trump for approving the declaration, saying it would "allow federal aid to arrive more quickly" after the storm passes.

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.

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