Airlines canceled more than 5,000 flights and Amtrak began suspending train service across the Northeast. New York moved to shut down subways, buses, and trains Sunday night and announced that schools would be closed on Monday. Boston, Washington, and Baltimore also called off school. Nonessential government employees in the nation's capital were told not to report for work Monday.
As rain from the leading edges of the monster hurricane began to fall over the Northeast, hundreds of thousands of people from Maryland to Connecticut were ordered to evacuate low-lying coastal areas, including 375,000 in Lower Manhattan and other parts of New York City.
Authorities warned that the nation's biggest city could get hit with an 11-foot wall of water that could swamp parts of Lower Manhattan, flood subway tunnels, and cripple the network of electrical and communications lines that are vital to the nation's financial center.
Sandy, a Category 1 hurricane with sustained winds of 75 m.p.h. as of Sunday evening, was expected to collide with a wintry storm moving in from the west and cold air streaming down from the Arctic. Forecasters said the combination could bring close to a foot of rain, a potentially lethal storm surge, and punishing winds that could cause widespread power outages that last for days. The storm could also dump up to 2 feet of snow in Kentucky, North Carolina, and West Virginia.
Louis Uccellini, environmental prediction chief for the National Oceanic and Atmospheric Administration, told the Associated Press that given Sandy's east-to-west track into New Jersey, the worst of the storm surge could be just to the north, in New York City, on Long Island, and in northern New Jersey.
Forecasters said that because of giant waves and high tides made worse by a full moon, the metropolitan area of about 20 million people could get hit with an 11-foot wall of water.
"This is the worst-case scenario," Uccellini said.
New York Mayor Michael Bloomberg warned: "If you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you. This is a serious and dangerous storm."
New York called off school Monday for the city's 1.1 million students and announced it would suspend all train, bus, and subway service Sunday night. More than five million riders a day depend on the transit system.
The New York Stock Exchange said it will shut down its trading floor Monday but continue to trade electronically.
Broadway also took the storm threat seriously, with theater owners canceling Sunday evening and Monday performances of shows such as The Book of Mormon, Once, and Mama Mia! long before a drop of rain fell in Times Square.
"The safety and security of theatregoers and employees is everyone's primary concern," said Charlotte St. Martin, executive director of the Broadway League, which represents producers.
Forecasts called for rain late Sunday or early Monday, and subway and public transportation service is to be halted Sunday evening.
Carnegie Hall canceled two concerts Sunday night and rescheduled a Monday concert.
As Americans braced Sunday for Hurricane Sandy, Haiti was still suffering.
Officials raised the storm-related death toll across the Caribbean to 65, with 51 of them in Haiti, which was pelted by three days of constant rains that ended Friday.
As the rains stopped and rivers began to recede, authorities were getting a fuller idea of how much damage Sandy brought on Haiti. Bridges collapsed. Banana crops were ruined. Homes were underwater. Officials said the death toll might still rise.
"This is a disaster of major proportions," Prime Minister Laurent Lamothe told the Associated Press, adding with a touch of hyperbole, "The whole south is under water."
The country's ramshackle housing and denuded hillsides are especially vulnerable to flooding. The bulk of the deaths were in the southern part of the country and the area around Port-au-Prince, the capital, which holds most of the 370,000 Haitians who are still living in flimsy shelters as a result of the 2010 earthquake.
Sandy also killed 11 in Cuba, where officials said it destroyed or damaged tens of thousands of houses. Deaths were also reported in Jamaica, the Bahamas, and Puerto Rico.