"Irene could become a major hurricane within the next day," said Miami-based center.
While the hurricane, the first of the Atlantic season 2011, lashed the Turks and Caicos and southeastern Bahamas with winds, rain and dangerous surf, residents in North Carolina and South Carolina were preparing for the arrival of the storm.
At 02.00 pm EDT (0600 GMT), Irene was located about 650 miles southeast of Nassau and about 1570 miles south of Cape Hatteras, North Carolina.
Irene, the ninth named storm of the season from June to November, is on track to become the first hurricane to reach the United States since Ike hit the Texas coast in 2008.
But weather forecasts suggest that the hurricane did not pose a threat to the oil and gas operations in the United States in the Gulf of Mexico.
Irene weakened on Tuesday to a Category 1 hurricane, but could re-strengthen into a powerful Category 3 storm with winds over 178 mph on Thursday, the NHC said.
The storm would approach the coast of North Carolina and South Carolina on Saturday morning.
After that, the New England region could be at risk of torrential rain, strong winds and flooding, said on Tuesday the administrator of the Federal States of Emergency Management (FEMA, for its acronym in English), Craig Fugate .
Major cities in the eastern United States as Washington and New York could also feel some impact, forecasters said.
North Carolina Gov. Bev Perdue urged residents to ensure they had food, water and supplies for three days.
Voluntary evacuations begin on Wednesday for areas of the Outer Banks in North Carolina, an extension of barrier islands and beaches that are popular during the summer holidays.
Irene struck the northeastern Caribbean islands earlier in the week. The first death was reported by the storm Tuesday in Puerto Rico, where a woman was swept away while driving on a flooded road near the river Loiza.
Heavy rains continued to fall on U.S. territory in the Caribbean, causing floods and mudslides.
About 300,000 residents were without electricity and 58,000 lacked drinking water.