In New York City, where 375,000 people were warned to evacuate, authorities moved to close the Holland Tunnel, which connects New York and New Jersey, and a tunnel between Manhattan and Brooklyn. Street grates above the subway were boarded up, but officials worried that seawater would seep in and damage the electrical switches.
In the morning, water was already splashing over the seawalls at the southern tip of Manhattan and had matched the levels seen during Hurricane Irene in August 2011. Still, people were out jogging, walking their dogs and even taking children out in strollers amid gusts of wind.
"We're high up enough, so I'm not worried about flooding," said Mark Vial, who was pushing his 2-year-old daughter, Maziyar, in a stroller outside their building, where they live on the 15th floor. "There's plenty of food. We'll be OK."
Water was already a foot deep on the streets of Lindenhurst, N.Y., along the southern edge of Long Island, and the canals around the island's Great South Bay were bulging two hours before high tide.
The major American stock exchanges closed for the day, the first unplanned shutdown since the Sept. 11 attacks in 2001. Wall Street expected to remain closed on Tuesday. The United Nations canceled all meetings at its New York headquarters.
New York called off school on both Monday and Tuesday for the city's 1.1 million students, and the more than 5 million people who depend on its transit network every day were left without a way to get around.
Sandy, a Category 1 hurricane, was blamed for 69 deaths in the Caribbean before it began traveling northward, parallel to the Eastern Seaboard. Forecasters said the combined Frankenstorm could bring close to a foot of rain in places, a potentially lethal storm surge of 4 to 11 feet, and punishing winds that could cause widespread power outages that last for days. Up to 3 feet of snow was forecast for the West Virginia mountains.