Florida's governor on Friday urged residents to stock up on at least a week's worth of food, water and medicine and to prepare to lose power and cellphone service for days after Hurricane Dorian makes landfall early next week.
The slow march and rising intensity of the storm, which is moving in a northwestern direction to the Bahamas, has alarmed forecasters who worry parts of Florida will be walloped by strong winds, a storm surge and heavy rain for an extended period.
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"I think there's a pretty high degree of certainty that this is going to be a major hurricane," Florida Governor Ron DeSantis told a news conference from the state emergency operations centre in Tallahassee. He said residents should prepare for a "multiday event."
Two thousand National Guard troops will have been mobilised for the hurricane by the end of Friday, with another 2,000 joining them on Saturday, Florida National Guard Major General James Eifert said.
Florida is under a declaration of emergency. In neighbouring Georgia, Governor Brian Kemp has declared a state of emergency in 12 counties to assist with storm readiness, response and recovery.
Dorian is also expected to bring a life-threatening storm surge and flash flooding to the northwestern Bahamas, the Miami-based National Hurricane Center (NHC) said in its latest advisory.
"Almost everyone has left, or is leaving today," said Pauline Powell, 26, who was on a family vacation at the Island Seas Resort in Grand Bahama when the storm started barreling toward the area's pristine beaches.
The Bahamas Ministry of Tourism and Aviation said hotels and resorts throughout that part of the island nation have activated hurricane response programs, which typically include boarding up beach-facing windows and encouraging guests to leave.
The Grand Bahama International Airport in Freeport will close Friday night and will not open until September 3, the ministry said in a statement.
Dorian began on Friday over the Atlantic as a Category 2 hurricane but was expected to strengthen and become a Category 3 later in the day. It had maximum sustained winds near 175km/h, according to the latest NHC advisory.
If, as expected, Dorian reaches Category 4 strength over the weekend, its winds will blow at more than 210 km/h. It is currently moving at a pace of 16km/h, giving it more time to intensify before making landfall.
Forecasters predicted it will be near the Florida peninsula late on Monday.
They expect a storm surge of as much as 3 to 4.5 metres above normal in some coastal waters of the Bahamas and Florida, and rainfall of about 15 to 30cm, with up to 46cm in some areas.
Some gas stations in Florida have run dry and others have long lines of cars, DeSantis said, adding that the state had eased regulations to allow higher-capacity trucks to transport fuel and to make it easier to bring in fuel from other states.
Gasoline prices at the pump are not expected to spike because of the storm, said Patrick DeHaan, head of petroleum analysis at GasBuddy.com.
"There are no refiners in Florida, there's only a pipeline, and I can't imagine that would be affected significantly. Fuel is flowing, and that's the most important factor," DeHaan said.
Colonial Pipeline, which delivers fuels such as gasoline and diesel from the Gulf Coast to markets across the southern and eastern United States, said it was operating normally. It had no plans to shut down ahead of Dorian's projected landfall.
Florida officials also were making sure all nursing homes and assisted living facilities had generators, and were checking with 107 facilities where information about generators was uncertain.
Earlier this week, police in Hollywood, Florida, charged four nursing home caregivers with causing the deaths of 12 patients who died in the sweltering heat of a post-hurricane power outage left by Hurricane Irma two years ago.
Officials from the Federal Emergency Management Agency, which was harshly criticized in 2005 for its slow response to Hurricane Katrina and its aftermath, briefed Congress on Friday on the steps they are taking to prepare for the storm.
FEMA has begun moving personnel and equipment into Georgia, including trucks and line crews who would help get electricity back up and running if there is a serious service interruption in Florida, according to a Democratic aide in the US House of Representatives familiar with the briefings.
President Donald Trump on Thursday cancelled a planned weekend trip to Poland, sending Vice President Mike Pence in his place, so he can make sure resources are properly directed for the storm.
"Now it's looking like it could be an absolute monster," Trump said in a video posted on Twitter, adding that food and water were being shipped to Florida.
Dorian could churn across dozens of launchpads owned by the National Aeronautics and Space Administration (NASA), the Air Force and companies such as Elon Musk's SpaceX and Jeff Bezos' Blue Origin.