The National Hurricane Center announced at 8 p.m. that Sandy had come ashore about five miles from Atlantic City. The sea surged a record of nearly 13 feet at the Battery, at the foot of Manhattan.
In an attempt to lessen damage from the storm, New York City's main utility cut power to about 6,500 customers in lower Manhattan, which includes Wall Street. Authorities worried that seawater would seep into the subway and cripple it, along with the electrical and communications systems vital to the nation's financial center.
As it closed in, Sandy knocked out power to more than 1.5 million people and smacked the boarded-up big cities of the Northeast corridor — Washington, Baltimore, Philadelphia, New York and Boston, with stinging rain and gusts of more than 85 mph.
At least four deaths were blamed on the storm in Maryland, Pennsylvania, Connecticut and New York. Among them were two people killed by falling trees.
As Sandy made its way toward land, it converged with a cold-weather system out of the west that turned into a fearsome superstorm, a monstrous hybrid consisting not only of rain and high wind but of snow. Forecasters warned of 20-foot waves bashing into the Chicago lakefront and up to 3 feet of snow in West Virginia.
Airlines canceled more than 12,000 flights, disrupting the plans of travelers all over the world, and storm damage was projected at $10 billion to $20 billion, meaning it could prove to be one of the costliest natural disasters in U.S. history.
President Barack Obama and Republican challenger Mitt Romney canceled their campaign appearances at the very height of the race, with just over a week to go before Election Day. The president pledged the government's help and made a direct plea from the White House to those in the storm's path.
"When they tell you to evacuate, you need to evacuate," he said. "Don't delay, don't pause, don't question the instructions that are being given, because this is a powerful storm."
Sandy, which killed 69 people in the Caribbean before making its way up the Atlantic, began to hook left at midday toward the New Jersey coast.
The storm lost its status as hurricane because it no longer had a warm core center nor the convection — the upward air movement in the eye — that traditional hurricanes have, but it was still as dangerous as it was when it was considered a hurricane, according to National Hurricane Center spokesman Dennis Feltgen.
Pete Wilson, who owns an antiques shop in Cape May, N.J., at the state's southern tip and directly in Sandy's path, said the water was 6 inches above the bottom edge of the door. He had already taken a truckload of antiques out but was certain he would take a big hit.
"My jewelry cases are going to be toast," he said. "I am not too happy. I am just going to have to wait, and hopefully clean up."
New Jersey Gov. Chris Christie said people were stranded in Atlantic City, which sits on a barrier island and was mostly under water late Monday. He accused the mayor of allowing them to stay there.
With the hurricane fast approaching, Christie warned it was no longer safe for rescuers, and advised people who didn't evacuate the barrier islands to "hunker down" until morning.
"I hope, I pray, that there won't be any loss of life because of it," he said.
While the hurricane's winds registered as only a Category 1 on a scale of five, it packed "astoundingly low" barometric pressure, giving it terrific energy to push water inland, said Kerry Emanuel, a professor of meteorology at MIT.
"We are looking at the highest storm surges ever recorded" in the Northeast, said Jeff Masters, meteorology director for Weather Underground, a private forecasting service. "The energy of the storm surge is off the charts, basically."
In New York City, authorities worried that salt water would seep through the boarded-up street grates and through the sandbags placed at subway entrances, damaging the electrical connections needed to operate the subway.
Hours before landfall, there was graphic evidence of the storm's power.
A construction crane atop a luxury high-rise in New York City collapsed in the wind and dangled precariously 74 floors above the street. Forecasters said the wind at the top the building may have been close to 95 mph.
Off North Carolina, a replica of the 18th-century sailing ship HMS Bounty that was built for the 1962 Marlon Brando movie "Mutiny on the Bounty" went down in the storm, and 14 crew members were rescued by helicopter from rubber lifeboats bobbing in 18-foot seas. Another crew member was found hours later but was unresponsive. The captain was missing.
At Cape May, water sloshed over the seawall, and it punched through dunes in other seaside communities. Sandy also tore away an old section of Atlantic City's historic boardwalk.
"When I think about how much water is already in the streets, and how much more is going to come with high tide tonight, this is going to be devastating," said Bob McDevitt, president of the main Atlantic City casino workers union. "I think this is going to be a really bad situation tonight."
In Maryland, at least 100 feet of a fishing pier at the beach resort of Ocean City was destroyed, and Gov. Martin O'Malley said there would be devastating flooding from the swollen Chesapeake Bay.
"There will be people who die and are killed in this storm," he said.
At least half a million people had been ordered to evacuate, including 375,000 from low-lying parts of New York City, and by the afternoon authorities were warning that it could be too late for people who had not left already.
Millions of people stayed home from work. Sheila Gladden evacuated her home in Philadelphia's flood-prone Eastwick neighborhood, which took on 5½ feet of water during Hurricane Floyd in 1999, and headed for a hotel.
"I'm not going through this again," she said.
Those who stayed behind had few ways to get out. New York's subways, which serve 5 million people a day, were shut down. The Holland Tunnel connecting New York to New Jersey was closed, as was a tunnel between Brooklyn and Manhattan, and the city planned to shut down the Brooklyn Bridge, the George Washington, the Verrazano-Narrows and several other spans because of high winds.
Stock and bond markets were closed Monday and Tuesday, the first shutdown since the days after the Sept. 11 attacks in 2001 and the first two-day closing of the stock market because of weather since a blizzard in 1888. The New York Stock Exchange is inside the mandatory evacuation zone in lower Manhattan, blocks from New York Harbor.
If the storm reaches the higher estimate of $20 billion in damage, that would put it ahead of Hurricane Irene, which raked the Northeast in August 2011 and caused $16 billion in damage. Hurricane Katrina, which killed 1,200 people, cost $108 billion.