Hurricane Joaquin gathered strength on Thursday as it pushed toward the Bahamas, with forecasts still inconclusive on whether the storm would slam into the US East Coast or head to sea without making landfall, the National Hurricane Center said.
Joaquin, the third hurricane of the 2015 Atlantic season, intensified into a major Category 3 storm on a scale of 1 to 5, with maximum sustained winds of 120 miles per hour (195 kph).
The storm was expected to become more powerful, possibly becoming a Category 4 over the next day, as it moves near or over parts of the Bahamas, the NHC said. Its center was about 10 miles (15 km) north of Samana Cays in the Bahamas early Thursday, moving west-southwest at 5 mph (7 kph).
"Joaquin is expected to intensify a little more in the next 12 to 24 hours while over very warm waters," the Miami-based NHC said.
The storm's current plodding pace suggests a prolonged period of hurricane conditions in parts of central and northwestern Bahamas, along with torrential rainfall and storm surges, before it makes a sharp turn north towards the United States.
Several models show Joaquin approaching the coast of the Carolinas at the weekend, losing strength as it moves offshore past Delaware and New Jersey early next week to head towards Long Island and New England.
Still, its exact trajectory remains unclear, with one often-reliable European model indicating it could cut a path out to sea.
"Confidence remains very low in the eventual track of Joaquin and any potential impacts for the United States," the NHC said on Thursday.
Residents on the islands closest to Joaquin's path, which include Rum Cay, Long Island, Exuma and Eleuthera, had stocked up on food and drink, and were boarding up homes and businesses.
The governors of New York and Connecticut and emergency-management officials in New Jersey - states that were hit hard by Superstorm Sandy in 2012 and already faced heavy rains unrelated to Joaquin on Wednesday - warned residents to begin preparations for a possible severe storm.
Virginia Governor Terry McAuliffe declared a state of emergency to deal with flooding this week and the possibility of the storm making landfall.
Heavy rains already falling over the northern Appalachians and New England this week greatly increase the chance of flooding if Joaquin comes ashore, forecasters at the privately-run Weather Channel said.
One person died after several cars were submerged in flash floods in South Carolina, local media reported on Thursday.
In October 2012, Superstorm Sandy struck the New York metropolitan area, killing more than 120 people and causing some $70 billion in property damage, primarily in New York and New Jersey.
US energy companies said they had learned lessons from Sandy and used the last three years to gird their oil, natural gas and power infrastructure to better withstand another storm.
New York power company Consolidated Edison Inc, which supplies power, gas and steam to more than three million customers in the New York City area, said it was three years into a four-year $2-billion plan to strengthen its energy infrastructure after Hurricane Sandy shut down the Big Apple.
Sandy, the worst storm in Con Edison's history, left about a million of its customers without power, with outages lasting a couple of weeks in the hardest-hit areas. Some customers of other utilities were without power for much longer.
The US East Coast has nine refineries with an operable capacity of about 1.3 million barrels per day, according to government data.