What makes the storm so dangerous and unusual is that it is coming at the tail end of hurricane season and the beginning of winter storm season, "so it's kind of taking something from both," said Jeff Masters, director of the private service Weather Underground.
Masters said the storm could be bigger than the worst East Coast storm on record — the 1938 New England hurricane known as the Long Island Express, which killed nearly 800 people. "Part hurricane, part nor'easter — all trouble," he said. Experts said to expect high winds over 800 miles and up to 2 feet of snow as far inland as West Virginia.
And the storm was so big, and the convergence of the three storms so rare, that "we just can't pinpoint who is going to get the worst of it," said Rick Knabb, director of the National Hurricane Center in Miami.
Officials are particularly worried about the possibility of subway flooding in New York City, said Uccellini.
New York Gov. Andrew Cuomo told the Metropolitan Transportation Authority to prepare to shut the city's subways, buses and suburban trains by Sunday, but delayed making a final decision. The city shut the subways down before last year's Hurricane Irene, and a Columbia University study predicted that an Irene surge just 1 foot higher would have paralyzed lower Manhattan.
Up and down the Eastern Seaboard and far inland, officials urged residents and businesses to prepare in big ways and little.
On Saturday evening, Amtrak began canceling train service to parts of the East Coast, including between Washington, D.C., and New York. Airlines started moving planes out of East Coast airports to avoid damage and adding flights out of New York and Washington on Sunday in preparation for flight cancellations on Monday.