Top developments:
Hurricane Irene zeroed in on land Saturday, losing some power but still threatening a catastrophic run up the East Coast as more than 2 million people were told to move to safer places to escape the massive storm.
New York City ordered America's biggest subway system shut down for the first time ever because of a natural disaster. A hurricane warning was issued for the city for the first time in two decades, and more than a quarter-million people in New York were ordered to evacuate.
The warning was in effect Friday from North Carolina in the south all the way to Massachusetts in the north. Officials declared emergencies, called up hundreds of National Guard troops, shut down public transit systems and begged hundreds of thousands of people to obey evacuation orders.
U.S. airlines were canceling at least 6,100 flights through Monday, grounding hundreds of thousands of passengers. The storm could strike major airports from Washington to Boston with heavy rain and dangerous winds.
The National Hurricane Center in Miami said early Saturday Irene had weakened to a Category 1 storm with top sustained winds down to 90 mph from 100 mph overnight, but warned that it would remain a hurricane as it moves up the mid-Atlantic coast, even after losing some more strength once it hits land.
"The hazards are still the same," NHC hurricane specialist Mike Brennan said. "The emphasis for this storm is on its size and duration, not necessarily how strong the strongest winds are."
As the storm's outermost bands of wind and rain began to lash islands off the coast of the southern state of North Carolina, authorities in points farther north begged people to get out of harm's way.
President Barack Obama, speaking from Martha's Vineyard Island off the coast of Massachusetts before ending his vacation early, said all indications point to the storm being a historic hurricane.
"Don't wait. Don't delay," said Obama, who decided to cut short his summer vacation by a day and return to Washington. "I cannot stress this highly enough: If you are in the projected path of this hurricane, you have to take precautions now."
Senior hurricane specialist Richard Pasch of the National Hurricane Center said there were signs that the hurricane may have weakened slightly, but strong winds continued to extend 100 miles from its center.
The storm's center was about 50 miles south of Cape Lookout, North Carolina, as of 4 a.m. ET Saturday as the storm lumbered north-northeastward at 14 mph.
Long before the storm's eye crossed the coastline, rain and tropical storm-force winds already were pelting North and South Carolina as Irene trudged north, snapping power lines and flooding streets. Officials warned of dangerous rip currents. Wind and rains knocked out power to about 45,000 customers along the coast, including a hospital.
Irene's wrath in the Caribbean, including Puerto Rico, the Dominican Republic and the Bahamas, gave a preview of what might be coming to the U.S.: Power outages, dangerous floods and high winds that caused millions of dollars in damage.
The U.S. East Coast, home to some of the country's most densely populated cities and costliest waterfront real estate, was expected to suffer a multibillion-dollar disaster. At least 65 million people are in its projected track.
Landfall was likely to be around 9 a.m. ET Saturday near Cape Lookout on North Carolina's Outer Banks, the National Hurricane Center said, but the storm's outer bands buffeted South Carolina Friday, flooding streets and downing power lines.
Massive evacuation effort
With more coastal cities ordering evacuations ahead of Hurricane Irene, residents and tourists alike from North Carolina to New York City were moving toward higher ground.
Traffic jams as long as 20 miles were reported and some service stations in New Jersey and other areas ran out of gasoline, according to the Oil Price Information Service, which tracks supplies and prices. Gasoline demand jumped 20 percent to 40 percent in Mid-Atlantic states, the service said.
Evacuation orders covered 1 million people in New Jersey, 550,000 in New York, 315,000 in Maryland, 300,000 in North Carolina, 200,000 in Virginia and 100,000 in Delaware.
"This is probably the largest number of people that have been threatened by a single hurricane in the United States," said Jay Baker, a geography professor at Florida State University.
New York, the nation's largest city, was among those announcing evacuations Friday.
"We've never done a mandatory evacuation before and we wouldn't be doing it now if we didn't think this storm had the potential to be very serious,'' Mayor Michael Bloomberg said in warning some 300,000 people living in low-lying areas.
Some 250,000 people in nearby Long Island were also told to clear out by Saturday afternoon.
The region can expect 4-8 feet of water surge, the hurricane center said, "with the highest values possible in western Long Island Sound and New York Harbor. These tidal conditions will be accompanied by large, destructive and life threatening waves."
This massive, wet and slow-moving hurricane is forecast to soak a Northeast saturated by earlier rain and may come ashore at a time when tides are unusually high, making storm surge even worse — 4 to 11 feet with waves on top, forecasters say.
"Water is the No. 1 killer," said retired National Hurricane Center Director Max Mayfield. "That's going to cause the greatest loss of life."
Below is a look at impacts and preparations by region:
New York City
New York City ordered more than 300,000 people who live in flood-prone areas to leave, including Battery Park City at the southern tip of Manhattan, Coney Island and the beachfront Rockaways. But it was not clear how many would do it, how they would get out or where they would go. Most New Yorkers don't have a car.
New York's two airports are close to the water and could be inundated, as could densely packed neighborhoods, if the storm pushes ocean water into the city's waterways, officials said.
The five main New York City-area airports planned to close to arriving passenger flights beginning at noon ET on Saturday, aviation officials said. The Port Authority of New York and New Jersey, which operates the airports and area bridges and tunnels, said Friday that many weekend departures already had been canceled in anticipation of the hurricane.
The suspension affects John F. Kennedy International and LaGuardia airports in New York City, Stewart International in the city's northern suburbs and Newark Liberty International and Teterboro in New Jersey. It applies to domestic and international flights.
Kennedy, LaGuardia and Newark are among the busiest airports in the nation. Together, all five airports serve 1.2 million flights and 104 million passengers a year.
"We do not have the manpower to go door-to-door and drag people out of their homes," Mayor Bloomberg said. "Nobody's going to get fined. Nobody's going to go to jail. But if you don't follow this, people might die."
Nearly 100 shelters were set to open, with a capacity of 71,000 people.
Meanwhile, Gov. Andrew Cuomo said subways, buses and commuter trains in the city, on Long Island and in the northern suburbs will be suspended starting around noon Saturday.
Cuomo added that 1,000 National Guard soldiers and airmen would help over the weekend.
The George Washington and Tappan Zee bridges, among others, were ordered shut if winds top 60 mph, as was the New York State Thruway.
Metropolitan Transportation Authority officials have said they can't run the transit system once sustained winds reach 39 mph, and they need an eight-hour lead time to shut it down.
Officials have entreated residents to take it upon themselves to get out early, but it remained unclear how many would heed the warnings that subways and buses might not be there for them if they waited.
A hurricane watch was in effect for New York City and Long Island for Sunday, with storm conditions possible Saturday night.
The MTA has never before halted its entire system — which carries about 5 million passengers on an average weekday — in advance of a storm, though the system was seriously hobbled by an August 2007 rainstorm that disabled or delayed every one of the city's subway lines.
On Thursday, Bloomberg ordered nursing homes and five hospitals in low-lying areas evacuated beginning Friday. At Coney Island Hospital, officials were transferring 241 patients to six hospitals outside the evacuation zone.
Even if the winds aren't strong enough to damage buildings in a metropolis made largely of brick, concrete and steel, a lot of New York's subway system and other infrastructure is underground and subject to flooding in the event of an unusually strong storm surge or heavy rains.
In the low-lying Financial District surrounding Wall Street, the New York Fed was readying contingency plans but expected normal functioning of its open market operations on Monday, a spokesman said.
The city had a brush with a tropical storm, Hanna, in 2008 that dumped 3 inches of rain in Manhattan.
In the last 200 years, New York has seen only a few significant hurricanes. In 1821, a hurricane raised tides by 13 feet in an hour and flooded all of Manhattan south of Canal Street, the southernmost tip of the city. The area now includes Wall Street and the World Trade Center memorial.
South Carolina
Hurricane Irene buffeted the coast of South Carolina on Friday, downing power lines, flooding streets and chewing away the sandy beaches that are the heart of the state's $14 billion tourism industry.
In the tourist district in Myrtle Beach late Friday, surfers and those who had walked down to the beach to watch the storm roiling the surf scattered. Cars crept along Ocean Boulevard with their lights on in the downpour. A wind gust of 62 mph was reported at Springmaid Pier.
Surf surged at the Caravelle Resort and flooded a nearby beach access.
At Edisto Beach, police reported waves of 10 to 12 feet and water on oceanside roads. At Folly Beach, significant erosion was reported. There was street flooding in Georgetown and standing water on roads up and down the coast.
North Carolina
Forecasters warned wind-whipped water could create a dangerous storm surge, with levels along North Carolina's Albemarle and Pamlico sounds rising as much as 11 feet.
Traffic was steady as people left the Outer Banks, which started getting heavy rain early Friday evening.
Tourists were ordered to leave the barrier islands Thursday, though local officials estimated Friday that about half the residents on two of the islands have ignored evacuation orders.
As a result, officials ordered dozens of body bags.
"I anticipate we're going to have people floating on the streets, and I don't want to leave them lying there," said Richard Marlin, fire chief for one of the seven villages on Hatteras. "The Coast Guard will either be pulling people off their roofs like in Katrina or we'll be scraping them out of their yards."
In Nags Head, police officer Edward Mann cruised the streets in search of cars in driveways — a telltale sign some planned to stay behind. He warned those that authorities wouldn't be able to help holdouts, and that electricity and water could be out for days.
Some told Mann they're staying because they feel safe or because the storm won't be as bad as predicted. Mann, 25, said some have told him they've ridden out more storms than years he's been alive.
Bucky Domanski, 71, was among those who told Mann he wasn't leaving.
"I could be wrong, but everything meteorologists have predicted never pans out," Domanski said. "I don't know, maybe I've been lulled to sleep. But my gut tells me it's not going to be as bad as predicted. I hope I'm right."
The National Weather Service reported the roof was blown off a Belhaven, N.C., dealership from Irene-spawned tornado.
Virginia
After the Outer Banks, the next target for Irene is the Hampton Roads region of southeast Virginia, a jagged network of inlets and rivers that floods easily. Emergency officials have said the region is more threatened by storm surge, the high waves that accompany a storm, than wind.
Gas stations there were low on fuel Friday, and grocery stores scrambled to keep water and bread on the shelves.
Few people were left along the coast of Virginia Beach, where officials ordered the mandatory evacuation of the city's Sandbridge section.
Similar orders were issued for at least 10 other localities and some roads inland had backups 7-8 miles long.
Maryland
The beach community of Ocean City was taking no chances, ordering thousands of people to leave.
"This is not a time to get out the camera and sit on the beach and take pictures of the waves," said Gov. Martin O'Malley.
Washington, D.C.
Irene forced the postponement of Sunday's planned dedication of the Martin Luther King Jr. Memorial on the National Mall. While a direct strike on the nation's capital appeared slim, organizers said the forecasts of wind and heavy rain made it too dangerous to summon a throng they initially expected to number up to 250,000 people.
A state of emergency was declared Friday as a way to marshal resources ahead of Irene.
New Jersey
Transit trains will stop running at noon Saturday, Gov. Chris Christie said Friday.
Aiming to speed up evacuations, Christie also suspended tolls on all parts of the Garden State Parkway south of the Raritan River and the Atlantic City Expressway.
Summer resort towns were emptying as officials ordered mandatory evacuation of the popular tourist areas along the state's coastal barrier islands.
Hundreds of thousands of people were likely to be affected by the orders, which included evacuation of such heavily visited towns as Wildwood, Ocean City and Avalon, all in Cape May County where the summer tourist population is typically 750,000 people.
Traffic was jammed for some 20 miles on the Garden State Parkway, said Mike Durkin, who drove home to Jenkintown, Pa., from the Jersey shore.
"I think there is a lot of nervous energy," he said. "There are people who have been there for 30 years who always rode out the storms before. A neighbor told me he just wasn't going to take a chance on this one though," he added.
All 11 of Atlantic City's casinos were ordered to close by noon Saturday. The city's casinos have shut down only twice before, in 1985 for Hurricane Gloria and in 2006 because of a state government shutdown.
Philadelphia
Mass transit in the city and suburbs will be shut down early Sunday morning, officials said Friday.
The city of Chester, which sits on the Delaware River just south of Philadelphia, ordered residents in flood-prone areas to evacuate by noon on Saturday.
Connecticut
Gov. Daniel Malloy declared a state of emergency and warned there could be prolonged power outages if Irene dumps up to a foot of rain on already saturated ground.
He said emergency responders must be ready in event of any evacuations from heavily developed urban areas. "We are a much more urban state than we were in 1938," he said, referring to the year that the so-called "Long Island Express" hurricane killed 600 people and caused major damage with 17-foot storm surges and high winds.
Boston
While some residents flocked to the supermarket for bottled water and nonperishable food, others rushed to the local hardware store.
"Our number of customers has tripled in the last day or two as people actually said 'wow, this thing is going to happen,'" said Jack Gurnon, owner of Charles Street Supply, a hardware store in Boston's wealthy Beacon Hill neighborhood.
Tape for windows, flashlights and batteries were flying off shelves, but Gurnon said people were worried about flooding and have been scooping up sump pumps, too.
Rhode Island
The towns of Narragansett and South Kingstown on Friday announced mandatory evacuations for residents in flood-prone areas for no later than 10 a.m. Sunday.
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Hurricane Irene
Florida
While avoiding a direct hit, the state did see the first U.S. injuries from Irene when eight people were washed off a jetty in West Palm Beach on Thursday by a large wave churned up by the storm. All survived.
Bahamas
The government said the storm earlier knocked out communications to islands such as Eleuthera and Abaco and that only partial reports of damage were so far available.
No reports of deaths or injuries were received, but some 180 homes on Acklins Island were destroyed or damaged.
The capital sustained relatively minor flooding and damage.
Insured losses in the Caribbean from Irene will be between $500 million and $1.1 billion, risk assessor firm Air Worldwide said on Friday, adding that the Bahamas will account for more than 60 percent of the loss.