Irene strengthened over warm seas around the Bahamas and reached major category 3 hurricane status, with peak sustained winds of 115 mph, the Washington Post says.
A direct hit on North Carolina's shore is possible, with some forecasters saying the hurricane is heading straight for Ocracoke Island, but Hurricane Irene could cause damage as far north as New England. All along the U.S. east coast, residents are bracing for torrential rain, flooding and punishing winds. In North Carolina, evacuations have begun.
Weather forecasters are predicting that Hurricane Irene will hit near the Outer Banks region of North Carolina on Saturday afternoon and then track up the coast to New England, but it may yet alter course.
National Hurricane Center Director Bill Read warned that Hurricane Irene could pose a "big threat" to the densely populated eastern seaboard, including New York, Reuters reports.
The tropical cyclone may reach category 4 levels with peak winds near 135 mph in the next few days, according to the Miami-based NHC, which also warned of an "extremely dangerous" storm surge.
"This is a huge storm," according to CNN meteorologist Jacqui Jeras. "The cloud field is more than 800 miles across. The tropical storm force winds extend out 200 miles from the center."
Irene is the first hurricane to threaten the U.S. this year, Reuters says.
Residents along the U.S. east coast are already shaken from Tuesday's 5.8 magnitude earthquake centered in Virginia, which was also felt in Washington, D.C., New York City and Boston.