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The science of Hurricane Sandy

Published: Tuesday, Oct. 30, 2012 8:32 a.m. CST
(MCT 2012)
Centerpiece graphic looks at the current status of Hurricane Sandy, potentially the most damaging storm in U.S. history; includes maps showing storm track, power outages, rainfall totals, storm surge flooding potential and information about closings and emergencies throughout the region.

(MCT) — WASHINGTON — Hurricane Sandy seems straight out of the latest Hollywood apocalyptic blockbuster. But a confluence of environmental and topographical characteristics helps explain its vast size, slow progress, storm surge and multiple methods of wreaking havoc on the coast and deep inland, scientists say.

Sandy began as a big storm when it came together in the Caribbean, said Katie Garrett, a meteorologist with the National Weather Service. It grew even larger as it moved north and into the mid-Atlantic, fed by unseasonably warm waters.

The tropical-storm winds that constitute Sandy stretch about 940 miles — greater than the distance from New York to Atlanta — said Jeff Masters, co-founder of the website WeatherUnderground.com and a former flight meteorologist “hurricane hunter” with the National Oceanic and Atmospheric Administration. Sandy is the largest such storm to make landfall on the Atlantic seaboard since the federal government began keeping records in 1988, he said.

Sandy’s course, from the southeast to the northwest, is not typical, according to Rick Knabb, director of NOAA’s National Hurricane Center in Miami. Although its path is “not 100 percent unprecedented,” it is unusual to have a storm of such size and strength coming inland so late in the year, Knabb said during a telephone press conference Monday.

Even when Atlantic storms come inland, they usually head out to sea. Some very powerful storms in recent years did not make landfall at all, kept away by onshore weather patterns. But Sandy has been pushed ashore into the mid-Atlantic states and New England because a high-pressure system near Greenland has blocked its progress eastward.

That shift toward the northwest has put Sandy on course to mesh with a cold front that began in California last week and has marched across the country, creating what Knabb and others call an unprecedented weather threat. The force of the eastward-moving front has slowed Sandy, Garrett said, and is changing the hurricane into a Nor’easter.

Already, Sandy has begun to lose traits typical of tropical storms, such as thunderstorms at its middle, Garrett said. Instead, Sandy’s merger with the cold front threatens severe snow in places. In West Virginia, 3 to 4 feet are predicted in some regions, with less snow in southwestern Virginia and western North Carolina.

“It’s not just a tropical storm, but a wind storm, a snow storm,” Garrett said.

Sandy could also produce record-setting storm surges. The swirling movement of its winds creates a big bulge of water that typically moves to the storm’s center. There, the low pressure in the atmosphere acts like a straw and pulls the water levels even higher, Masters said. If a storm is farther out to sea, that bulge would eventually sink. But because Sandy has moved to shallower inland waters, that bulge has nowhere to go but toward shore, he said.

The slowness of the storm means it could sit over the East Coast through several high tide cycles. Scientists are predicting 10- to 11-foot storm surges, including high tide conditions, in places like New York and New Jersey. Monday night’s full moon could add another foot to the surge, Knabb said. Finally, many inlets and bays in the mid-Atlantic are funnel-shaped, which means water can surge in easily, but getting out is a challenge.

Knabb said he didn’t expect water levels to return to normal until Wednesday.

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