Irene, a major Category 3 hurricane now battering the low-lying Bahamas southeast of Florida, was expected to make landfall on Saturday in North Carolina and follow the heavily populated mid-Atlantic seaboard north where Washington and New York were vulnerable.
The Washington Post warned the 5.6 million residents in the Washington metropolitan area to prepare for a "pretty big storm" to hit the area on Saturday and Sunday.
The National Weather Service issued a flash flood watch and hazardous weather outlook for the capital and nearby Virginia and Maryland for a storm system preceding Irene's arrival.
"Some of these thunderstorms may become severe ... producing damaging wind gusts and locally large hail," the service said in an alert published on its website.
Electric power provider Pepco Inc said it had requested 600 emergency workers from other regions, and had already deployed 150 of them, to prepare for Irene's heavy rain and high winds that "could cause widespread and extended power outages.
"The subsequent restoration could be a multiday event," the utility warned customers on its website, urging them to ensure adequate supplies of prescription medicines and infant supplies.
Railway operator Amtrak cancelled trains operating south of Washington for Friday, Saturday and Sunday.
"Additional cancellations may be necessary in the coming days as the major storm moves north," the railway said in an alert on its website.
Most schools in Washington had reopened on Thursday after being closed two days for safety inspections of 126 school buildings due to Tuesday's 5.8 magnitude quake. The tremor was centred in Mineral, Virginia, about 145km southwest of Washington.
The largest quake in Virginia since 1897 caused damage to well-known buildings, including cracks to the top of the Washington Monument, a prime tourist attraction.
