By Allen G. BreedNEW YORK -- Gaining strength and threatening 50 million people, Hurricane Sandy chugged north Monday, raking ghost-town cities along the Northeast corridor with rain and wind gusts. Subways and schools were closed, the floor of the New York Stock Exchange was deserted, and thousands of people fled the low-lying coast. Forecasters expected the monster hurricane to make a westward lurch and aim for the coast of New Jersey, blowing ashore Monday night or early Tuesday and combining with two other weather systems to create an epic superstorm. Its projected path put New York City and Long Island in the danger zone for a huge surge of seawater made more fearsome by high tides and a full moon. "This is the worst-case scenario," said Louis Uccellini, environmental prediction chief for the National Oceanic and Atmospheric Administration. Because the storm is so big, with tropical storm-force winds extending almost 500 miles from its center, it could upend daily life for days for people from the East Coast to the Great Lakes. As much as 3 feet of snow was forecast for the West Virginia mountains. Millions of people in the Northeast stayed home from work. Subways, buses and trains shut down, and more than 7,000 flights in and out of the East were canceled, snarling travel around the globe. Hundreds of thousands of people were under orders to flee the coast, including 375,000 in lower Manhattan and other parts of New York City, but authorities warned that the time to get out was short or already past. "I think this one's going to do us in," said Mark Palazzolo, who boarded up his bait-and-tackle shop in Point Pleasant Beach, N.J., with the same wood he used in past storms, crossing out the names of Hurricanes Isaac and Irene and spray-painting "Sandy" next to them.