What was once Hurricane Sandy has already affected more than 50 million people in 20 eastern U.S. states, leaving millions literally powerless and flooding New York City with a record-breaking storm surge.
But the superstorm, today downgraded to a post-tropical cyclone, isn't finished yet. Sandy's secret? Size matters.
As of 11 a.m. this morning, Sandy was about 120 miles (193 kilometers) east of Pittsburgh and moving westward at about 10 miles (16 kilometers) an hour. Even so, the storm's vast reach means New York's Long Island was still seeing storm surge flooding early today.
Tim Morrin, a meteorologist at the National Weather Service Forecast Office in New York City, said Sandy's winds-though not as strong as when the storm made landfall in New Jersey last night—were still running around 40 miles (64 kilometers) an hour today. That's enough to topple trees and possibly damage or destroy some buildings, Morrin said.
Elsewhere, snow continued to fall in the mountains of Virginia, West Virginia, and North Carolina. (Get our tips on hurricane preparedness.)
The storm is expected to continue moving westward until tonight, when it will turn north, cross Lake Ontario, and move into Canada Wednesday morning. As it grinds on, Sandy's remnants will continue causing problems—such as inland flooding and winds as high as 65 miles (104 kilometers) an hour on some of the Great Lakes and in coastal New England.
"The diameter of the winds," Morrin noted, "stretches hundreds and hundreds of miles in all directions."
(Get the inside story of forecasting killer hurricanes.)
What Put the "Super" in the Superstorm?
The reason Sandy is lingering is simple.
"It's a huge storm," said Miles Lawrence, a meteorologist for Early Alert, an emergency management consulting company in Florida. "There's still weather down in Georgia—not severe weather—that is associated with this storm. It's covering a quarter of the country now."
The reasons it became so big, however, are a little more complex. (Related: "Hurricane Sandy: Why Full Moon Makes 'Frankenstorm' More Monstrous.")
Sandy began on October 22 as a tropical depression in the warm waters of the southern Caribbean Sea. Its transition into a megastorm began a few days later, when the storm started moving away from the Bahamas.
As the center of the storm moved north of the North Carolina coast, Sandy benefitted from conditions that probably would not have been present had the storm formed during the summer.
Eric Blake, a meteorologist at the National Hurricane Center in Miami, said there's a brief period in the fall when a warm tropical system can interact with cold fronts moving down from Canada. When this happens, a "hybrid" storm can form that has the characteristics of both a hurricane and a winter storm.
Sandy became such a storm as it moved northward, interacting with a cold front over Canada that prevented the storm from curving out to sea and instead pushing it toward New Jersey.
The storm also came under the influence of the jet stream, an upper-level air current that usually flows from west to east. But the stream had shifted so that it was, and is, flowing from the southeast to the northwest. This unusual configuration created a vacuum above the storm that drew air upward, allowing Sandy to strengthen. (Watch hurricane videos.)
Weather conditions in the coastal areas already devastated by Sandy are expected to start improving Wednesday as the Northeast begins to clear the wreckage. The hybrid storm that was Sandy is expected to continue its northeastward march until it finally dissipates over either Canada or the North Atlantic.
Willie Drye has been writing about hurricanes and other topics for National Geographic News since 2003. Follow his blog, Drye Goods.
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