Downgraded a notch to a Category 1 storm, Hurricane Irene made landfall on the Outer Banks of North Carolina just after dawn Saturday, with its leading edge already delivering gusting winds and showers to the Washington area and beaches from Virginia north to Delaware.

The brunt of the storm was moving north from Cape Hatteras and was expected to arrive in the Washington area late Saturday and into Sunday morning before heading toward New York and New England.

Hurricane-force winds battered the North Carolina coast, knocking out power in places.

Officials in southeast Virginia prepared Saturday morning to close two key tunnels in the Norfolk and Hampton Roads area and they warned drivers to stay off the roads until the storm passed.

On Friday, tens of thousands of people began evacuating low-lying areas from the Carolinas to Manhattan as a vicious hurricane moved up the East Coast.

President Obama urged people to get out of the way of Hurricane Irene before he and his family abandoned their Martha’s Vineyard vacation to return to the White House.

“All indications point to this being a historic hurricane,” said Obama, who conferred with key response team officials and had a teleconference with East Coast governors Friday.

The storm was on a track that experts have feared for decades as they watched the rapid expansion of coastal resorts and housing developments in the lowlands behind them. They have worried that a storm tracking along the shore line, renewing its force over the warm Atlantic and then ripping with each rotation like a circular saw into coastal areas, could produce unprecedented devastation.

“It looks like the track of Irene is going to have a major impact along the East Coast starting in the Carolinas all the way up through Maine,” said Craig Fugate, director of the Federal Emergency Management Agency.

Irene weakened to a Category 1 storm — still with a strength of 90 mph — at 3 a.m. Saturday as it neared North Carolina coastline, the National Hurricane Center said.

The storm was expected to be over Cape Hatteras by 2 p.m. Saturday. By then, the outlying showers in its advance should be moving through Virginia and into the D.C. metro area. However, light rain began to fall on the lower parts of the Chesapeake Bay region and the beaches of Delaware before 6 a.m. Saturday, earlier than forecast.

The worst of it should pass over the area between nightfall and into Sunday morning, with the reaches between Interstate 95 and the beaches facing the most rain and highest winds.

By Sunday afternoon, if the current track holds, the storm will hit New York City. On Friday, plans were made to shut down the city’s subway system and, for the first time in memory, people were ordered to evacuate flood-prone coastal areas in Brooklyn, Queens, Staten Island and the financial district in Lower Manhattan.

On Friday, as people streamed from evacuated coastal areas in North Carolina, Delaware and the Eastern Shore of Maryland and Virginia, officials in the Washington region warned that power outages might last for days after the storm blows through.

District Mayor Vincent C. Gray (D) joined governors of the adjoining states in declaring an official emergency. Virginia Gov. Robert F. McDonnell (R) sent many state employes home early Friday and Maryland Gov. Martin O’Malley said, “All of us are going to be in for a long haul [Saturday] night.”

He cautioned that mobile phone service could be lost if the storm damages cell towers.

Acquiring sandbags, electrical generators, provisions and flashlights was the order of the day, and people moved double-time through stores as employees raced to restock shelves. In the District, a line of cars wrapped around the corner of New Jersey Avenue as dozens of people waited to pick up sand bags near the Navy Yard Metro station.

The weekend’s planned events were a washout, with most Saturday events canceled, as well as virtually everything on Sunday. The dedication of the Martin Luther King Jr. Memorial, the D.C. Rally for Full Democracy and the National Action Network March scheduled for this weekend were called off.

Some events — like the opening of college dorms — were moved up to Friday to get ahead of the storm. Plans were made to transfer the last remaining patients at Walter Reed Army Medical Center by ambulance to the National Naval Medical Center in Bethesda on Saturday morning, one day ahead of schedule.

Doctors alerted women who are due to give birth in the next week or so to have their hospital bags packed a little early. The drop in barometric pressure associated with the hurricane could cause a woman’s water to break early. Hospital officials said they are aware that lowering of atmospheric pressure tends to result in a spike in births.

“It’s along the same line as what happens when there’s a full moon,” said Matt Brock, a spokesman for Washington Hospital Center.

Pepco officials urged patience as they anticipate a “widespread” and “multi-day” power outage as Hurricane Irene approaches a region in which the company has 778,000 customers in the District and Montgomery and Prince George’s counties.

“This is a huge event,” said Joe Rigby, chief executive of Pepco’s parent company, Pepco Holdings.

Rigby said the company has 150 out-of-state workers inbound to help a beefed up staff of about 815 Pepco employees and pool of contractors that have been in the area for several months helping with tree trimming and repairs as part of a multimillion-dollar plan to improve service. By Sunday, there should be about 1,300 people working on power restoration in the Washington area, Rigby said.

Rigby and Thomas Graham, Pepco Region president, said the call centers that respond to customers can handle double the capacity of a year ago.

Dominion Virginia Power, which serves North Carolina and Virginia regions, has been tracking the hurricane for more than a week and expects Norfolk, Virginia Beach and eastern North Carolina areas to feel the greatest impact from the storm.

Baltimore Gas and Electric said Friday that central Maryland should anticipate widespread power outages lasting several days starting Saturday afternoon or evening, leaving an estimated 500,000 without power.

The Maryland Transportation Authority said the Chesapeake Bay Bridge will remain open unless sustained winds reach 55 miles per hour. Forecasts indicate winds could reach that speed as early as Saturday afternoon.

“If you are planning to cross the Bay Bridge, don’t wait until the last minute to do so,” said Maryland Transportation Secretary Beverley K. Swaim-Staley. “Certainly no later than early [Saturday] morning to make sure that you are able to cross before the weather deteriorates.”

Virginia Department of Transportation crews planned to begin emergency operations Saturday morning, working in 12-hour shifts throughout the storm. They will suspend emergency response activities in the event of sustained tropical storm winds of 39 mph or higher.

VDOT generally does not close bridges, ramps or roads unless there is high water, strong sustained winds, pavement or structural damage, or downed trees and other debris blocking roads. VDOT prepares year-round for hurricanes by training, conducting drills and performing simulation studies.

Metro chief spokesman Dan Stessel said Friday that “we do not expect above-ground rail service to be suspended unless conditions end up being worse than expected. If there are any changes, we’ll let folks know at”

National Cathedral officials feared the hurricane would exacerbate damage done to the gothic church by Tuesday’s earthquake.

“If the earthquake hadn’t occurred, there wouldn’t be any issues with regard to the hurricane,” said Richard Weinberg, National Cathedral’s spokesman. “The cathedral can withstand heavy winds. But because the elements that are up there are not secure, the winds from the hurricane could cause further damage.”

Crownsville insurance agent David Mathes said that with the storm, an already busy week will get even more hectic.

“With the earthquake on Tuesday and the impending storms, we have never been so busy answering questions about what is covered and what is not,” Mathes said.

As Margaret Douglas loaded her van with enough food to last several days at Balducci’s on Old Georgetown Road in Bethesda, she said a recent $8,000 investment gave her storm confidence.

“I bought a whole house generator, that’s why,” she said. Last year, she lost the food in her refrigerator and freezer three times during separate power outages.

Patricia Capiro and Manny Fantis spent a year planning their Saturday wedding in Rehoboth Beach, where Capiro grew up. By Thursday afternoon, the linens were pressed, the flowers were ready and the cake was in the refrigerator. Then the limo company cancelled. The band’s hotel rooms were cancelled. One guest after another said they wouldn’t be able to make it.

Capiro, a news producer at NBC 4, kept calling the station’s meteorologists to ask for updates. “It just kept getting worse and worse,” said the 29 year-old bride. Finally, authorities told the couple’s venue, the Rehoboth Beach Yacht and Country Club, that it needed to shut down for the weekend.

Capiro cried and then started calling guests and vendors to tell them the wedding was off. Fantis is the executive Web producer at Channel 9, and many of their friends — colleagues at the two television stations — will spend the weekend covering the storm instead of celebrating.