At 11 a.m., the Category 1 hurricane was 205 miles southeast of Atlantic City, New Jersey, and 260 miles south-southeast of New York City, the National Hurricane Center said. Maximum sustained winds were 90 mph, and Sandy was moving north-northwest at 18 mph.
It was predicted to turn toward the northwest during the day, and then turn toward the west-northwest Monday night. Its center was expected to make landfall along or just south of the coast of New Jersey on Monday evening or night.
Gale-force winds were already occurring over parts of the Mid-Atlantic states -- from North Carolina up to New York's Long Island. The winds were expected to spread later in the day over more of the Mid-Atlantic coast, New York City and southern New England.
Storm surge -- the combination of a storm and a high tide -- "will cause normally dry areas near the coast to be flooded," the weather service said. It said water depths could reach 6 to 11 feet along Long Island Sound and New York Harbor.
"Elevated waters could occur far removed from the center of Sandy," it added.
Three to six inches of rain were expected over far northeastern North Carolina, with isolated maximum totals of eight inches possible, it said.
Four to eight inches of rain were expected over portions of the Mid-Atlantic states, with isolated amounts of 12 inches possible.
Two to three feet of snow were expected to accumulate in the mountains of West Virginia and one to two feet in the mountains of southwestern Virginia to the border with Kentucky. One to one-and-a-half feet of snow were expected in the mountains near the North Carolina-Tennessee border.
But even with Sandy hundreds of miles offshore, officials were warning of its life-threatening storm surge flooding portions of the Mid-Atlantic, including low-lying areas of New York and New Jersey.
Michelle Franchaise of Ocean Gate was among the tens of thousands of New Jersey residents ordered to leave their coastal communities Sunday.
She and more than 180 others hunkered down at an emergency shelter in Toms River, New Jersey, to ride out the storm. She selected one of the 250 green cots that lined the floor.
"I'm very concerned when I see the map, and I see how big it is," she said. "I think I'm in good hands here. I think I'm safe."
At least 60 people at the Toms River shelter took their pets with them.
"The cops came around and were like, 'If you don't leave, you're going to be arrested,' " said a woman as she cradled one of the four kittens she had taken with her. "I couldn't leave without them."
Bracing for the worst
By early Monday, the city that never sleeps bedded down after halting service on its bus and train lines, closing schools and ordering about 400,000 people out of their homes in low-lying areas of Manhattan and elsewhere.
The process of halting subway service in New York began Sunday night. Other mass transit systems suspended their services Monday, including Washington's Metro service and Southeastern Pennsylvania Transportation Authority trains and buses in and around Philadelphia.
In Sea Bright, New Jersey, Yvette Cafaro scrawled a plea on the plywood that covered her burger restaurant: "Be kind to us Sandy."