Mayor Michael R. Bloomberg urged residents in low-lying areas to be out by 7 p.m., the same time that transit service would be suspended.
“We’re going to have a lot of impact, starting with the storm surge,” said Craig Fugate, the administrator of the Federal Emergency Management Agency. “Think, ‘Big.’ ”
Though the hurricane is not expected to make landfall until sometime late Monday, coastal regions will be hit by gale-force winds, heavy rain and possible flooding as early as Sunday, said Rick Knabb, the director of the National Hurricane Center. Tropical storm conditions were being felt in parts of North Carolina on Sunday, though the storm was 250 miles off the coast.
“Sandy is a large hurricane, and large systems pose multiple hazards for more people than smaller systems of comparable intensity,” Dr. Knabb said.
Forecasters warned that it could ravage areas far beyond the projected trajectory, and they urged people to heed evacuation calls and to prepare for the worst.
In its latest report, the Hurricane Center said the storm surge could be as high as 11 feet above normal along Long Island Sound and Raritan Bay — a significantly higher forecast than in previous reports — and warned that major flooding could occur across a broad area of the East Coast. Forecasters also expected torrential rains in some regions, which would add to the flooding.
And then there is the snow.
As Hurricane Sandy approaches land, it will be drawn into a system known as a midlatitude trough, a severe winter storm that is moving across the country from the west. A burst of arctic air is expected to sweep down through the Canadian Plains just as they are converging. That could lead to several feet of snow in West Virginia and Kentucky and lighter amounts in Pennsylvania and Ohio. Temperatures could drop into the mid-20s.
In announcing the transit shutdown, Gov. Andrew M. Cuomo of New York said it was unsafe to operate trains in high winds. He also said the closing was intended as a signal to discourage New York-area residents from being “up and about.”
The subway system will begin to curtail service at 7 p.m., and the transit authority’s railroads, Metro-North and the Long Island Rail Road, will begin their final trips at the same time, some buses may remain in service until 9 p.m. (It takes about eight hours for the subways to be shut down, but only six for the bus system.)
“The transportation system is the lifeblood of the New York City region, and suspending all service is not a step I take lightly,” Mr. Cuomo said. “But keeping New Yorkers safe is the first priority, and the best way to do that is to make sure they are out of harm’s way before gale-force winds can start wreaking havoc on trains and buses.”
Joseph J. Lhota, the chairman of the Metropolitan Transportation Authority, said he expected the transit systems to restore at least some service about 12 hours after the storm passes over the area, but he warned that the city could be without transit for as many as two full working days. “I do think Monday and Tuesday are going to be difficult days,” Mr. Lhota said.
He said that if sustained winds reached 39 miles per hour, drivers on the bridges would be required to slow down. At 60 m.p.h., they would be closed to traffic. Outbound trips on the authority’s paratransit service, Access-A-Ride, were scheduled only until noon on Sunday; return trips would continue until 5 p.m.
A full-scale closing of the subways, which run 24 hours a day, had never been ordered until August 2011, as Tropical Storm Irene approached. That storm toppled trees onto the tracks of the commuter rails, flooded train yards and led to millions of dollars in lost fares for the authority, which submitted $65 million in insurance claims this year to recover those losses. The closing this year could prove even more devastating.
Mayor Bloomberg said that city offices would be open Monday and that “city employees should make every effort to report to their jobs on Monday morning.”
City parks and marinas would close at 5 p.m. Sunday, he said. The New York Stock Exchange said in a statement that it would remain open on Monday, but would continue to monitor the weather.
He called for a mandatory evacuation of Zone A, low-lying areas that include the Rockaways, Coney Island and Red Hook after he revised his assessment of the storm’s potential impact. He said about 375,000 people would have to evacuate. (A guide to those areas can be found here.)
He added that those who ignored the evacuation order were “not going to get arrested, but they are being, I would argue, very selfish.”
Governors across the region have declared emergencies, and federal officials have issued urgent warnings for people to prepare.
From Plymouth, Me., to Cape Hatteras, N.C., residents boarded up windows; stocked up on water, batteries and food; and prepared to hunker down. Airlines encouraged people with flights scheduled in the next few days to change their plans and waived cancellation fees. Though airports remained open, major airlines including Delta, United and American, announced that flights would be canceled.
American Airlines said it canceled 140 flights on Sunday and would cancel an additional 1,431 flights from Monday through Wednesday.
Amtrak has also shut down train service to parts of the East Coast, including between Washington and New York.
At supply stores across the region, generators and other goods were snapped up in preparation for the possibility of extended power failures.
Tens of thousands of people who live on the state’s densely populated barrier islands — from Sandy Hook to Cape May — were evacuating on Sunday in compliance with an order issued by Gov. Chris Christie.
The evacuation included the 40,000 residents of Atlantic City, where the casinos closed at 3 p.m. on Sunday. All New Jersey Transit service, including buses and rail and light rail lines, were to be suspended starting at 4 p.m.
In Rehoboth Beach, Del., a long line of cars snaked out of town, adhering to the evacuation order announced Saturday night. But some families stopped to take one last picture of the pounding surf.
“It’s just magnificent looking at this,” said Lori Watson, a Rehoboth Beach resident who lives several miles inland and was not evacuating.
Federal officials, in a briefing with reporters on Sunday, could not say for certain where the impact would be worst. Dr. Knabb of the National Hurricane Center said the storm is most likely to come ashore sometime late Monday between Long Island and the Delmarva Peninsula. But he said the storm’s effects would stretch far up and down the coast and deep inland.
Reporting was contributed by Matt Flegenheimer and Colin Moynihan from New York; Brian Stelter from Rehoboth Beach, Del.; Jon Hurdle from Philadelphia; Stacey Stowe from Yonkers; and Angela Macropoulos from Long Island