MIAMI — Officials and residents from Florida to the Carolinas stocked up on supplies, dusted off evacuation plans and readied for the worst as Irene, the first hurricane to threaten the U.S. in three years, churned over tropical waters Tuesday after cutting a destructive path through the Caribbean.

Federal officials warned the storm could flood streets and knock down power lines as far north as New England. Irene lost some of its punch Tuesday afternoon and was downgraded to a Category 1 hurricane as it lashed the Turks and Caicos Islands, but the storm remains likely to regain strength and become a major hurricane before making a U.S. landfall.

The hurricane has raked the Caribbean and could cause serious problems along the entire Eastern Seaboard, Federal Emergency Management Agency administrator Craig Fugate said Tuesday during a conference call with reporters. Fugate urged people not to become complacent, even though the forecast is still uncertain and the storm may be days from hitting the U.S.

“We need to remind people, hurricanes are not just a Southern thing. This could be the mid-Atlantic and the Northeast coast,” Fugate said. “We’ve got a lot of time for people to get ready, but we don’t have forever.”

Officials on North Carolina’s Ocracoke Island were taking no chances. Tourists were ordered to evacuate today, while residents were told to be off the island by Thursday, said Tommy Hutcherson, who serves on the board that issues such orders.

Hutcherson, who owns the Ocracoke Variety Store, said officials have to issue orders early because of the limited capacity of the ferries. But that doesn’t mean everyone will leave.

“I’ll be here,” said Hutcherson, a 29-year resident who has ridden out numerous past storms. “A lot of the locals will choose to stay.”

The barrier island is only accessible by boat. It is 16 miles long and mostly undeveloped, with a town at the southern tip.

It’s possible Irene will make landfall over the North Carolina coast sometime Saturday, then move to the north near the Chesapeake Bay. However, because such projections can be uncertain, it’s also possible Irene could straddle the coast.

Fugate and National Hurricane Center director Bill Read said Irene could cause problems even over open water. New England is particularly vulnerable to heavy rains because the soil is already saturated from summer storms, which could raise the threat of flash flooding.

Irene has already wrought destruction across the Caribbean, giving a glimpse of what the storm might bring to the Eastern Seaboard. In Puerto Rico, more than a million people were without power, and President Obama declared an emergency there. Hundreds were displaced by flooding in the Dominican Republic.