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Mysterious Northeast Floods Caused by Weird Winds

Flooding and high tides along the East Coast in 2009 and 2010 were triggered by a major change in wind patterns and offshore currents. Continue reading →

Mysterious flooding and high tides along the East Coast in 2009 and 2010 now have an explanation: a major change in the Atlantic Ocean's wind patterns and warm-water currents.

At the time, the unusually high tides caught people by surprise. Now, researchers know why the ocean was flooding beaches and barrier islands: Sea levels temporarily jumped by up to 2 feet (61 centimeters) above the high tide mark, as measured by tide gauges along the Atlantic Coast from Maine to Florida. Over the two-year period, coastal sea levels rose an average of 4 inches (10 cm) from New York to Newfoundland, Canada, researchers reported today (Feb. 24) in the journal Nature Communications.

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"This extreme sea level rise is unprecedented in tide gauge records," said study co-author Jianjun Yin, a University of Arizona geosciences professor who specializes in climate modeling. "This is a one-in-850-year event, based on the past records."

The unexpected surge was caused by a major slowdown in the Gulf Stream, one of the Atlantic Ocean's great currents, the new study reports. About two months before sea levels spiked along the East Coast, the strength of the Atlantic meridional overturning circulation (AMOC) declined by 30 percent, according to earlier research by other scientists. The Gulf Stream, which is part of the AMOC, flows from the tip of Florida up the coast to Newfoundland, Canada. [7 Ways the Earth Changes in the Blink of an Eye]

The AMOC brings warm water from the tropics to the North Atlantic and the polar regions, where the water cools and sinks, and then flows back to the tropics via the deep ocean. These water temperature differences drive the current. In 2009 and 2010, the current's speed slowed down because warmer-than-average temperatures in the Labrador Sea (between Canada and Greenland) backed up the current, creating an effect similar to a jam on a highway overpass, said lead study author Paul Goddard, a University of Arizona geology graduate student. This slowdown piled up water in the North Atlantic, just like cars trapped in traffic.

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"The anomalous heat made the surface waters less dense and less likely to sink, and it created a bottleneck," Goddard said.

Although the backed-up current can trigger coastal sea level rise on its own, the researchers think the extreme sea level jump seen in 2009 and 2010 was triggered by persistent winds that pushed the water up against the Atlantic Coast.

The steady winds were associated with a negative phase of a natural climate pattern called the North Atlantic Oscillation (NAO). The NAO flip-flops between negative and positive phases. In years with a negative NAO, winds drive water onto the northeast coast, Yin said.

Although temporary, the rapid sea level rise seen during the study can threaten coastal homes and businesses, especially if the spikes coincide with severe storms.

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"If this type of situation occurs more often in the future, there's always a chance of it being superimposed on a storm surge," Goddard said.

Climate models suggest that sea level anomalies may become larger and more frequent this century as global warming alters ocean temperatures, Yin said. In the Atlantic, such changes will push sea levels higher along the East Coast, the researchers said.

Eight of the top 10 U.S. cities that have seen an increase in coastal flooding are on the East Coast, according to a National Oceanic and Atmospheric Administration report published in August 2014.

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On the Ground: Hurricane Sandy in Images The 20 Cities Most Vulnerable to Flooding In Images: Extreme Weather Around the World Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Originally published on Live Science.

Coastal floods in Annapolis, Md., in 2012.

If you were interested in freaky weather, 2014 had it all, including some new words for the popular lexicon: Polar vortex, lake effect snow, bomb cyclone, Snovember and, of course, the worst drought in California in 1,200 years. In this shot, a bolt of lightning hits the antenna on top of the Empire State Building on July 15 in New York City.

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An image from a NOAA satellite shows the polar vortex, the weird atmospheric twitch that flooded into the United States in early 2014, over North America.

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Steam rises from Lake Michigan toward the Chicago skyline on a day when the temperature was -18 and -43 with the wind chill. The polar vortex took the fall for this one.

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Snowfall was dramatic in 2014, but the hurricane season was notable for being unusually light. Hurricane Arthur (above in a NASA satellite photo) was the only storm to make landfall in the United States this season. The storm in July clobbered coastal North Carolina on July 4 with Category 2 winds of about 100 miles per hour, causing $21 million in damage.

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A buoy sits on dry cracked earth on a dry inlet of Shasta Lake on Aug. 30 in Lakehead, Calif. The state suffered a fourth year of one if its worst droughts on record. The drought was fueled by a spate of disappointing winter rainy seasons that have left meager snowpacks and diminished reservoir levels, combined with record-warm temperatures that have driven demand for increasingly precious water, spurring a series of conservation measures around the state.

In this image, captured in infrared light by the National Oceanic and Atmospheric Agency's GOES-East satellite on Nov. 18, the cold air over the central and eastern United States looks like a gray-white blanket.

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More than 7 feet of snow fell on parts of Buffalo, N.Y., in part due to a weather event called lake effect snow. It's a highly localized snowfall, which appears when cold air masses move over warmer lake waters. Longtime residents described the blast of winter weather as the worst in memory.

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Australians were treated to a bizarre sight in the sky this year: a fallstreak hole, which forms from droplets in the cloud that are below freezing, but haven't yet frozen.

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In November, Super Typhoon Nuri, a massive, exceptionally violent tropical cyclone, started out near the Philippines and then barreled across the Pacific to slam into Alaska’s Aleutian Islands. One of the biggest typhoons ever to blow outside the tropics, Nuri measured about 2,000 miles across, and it whipped the U.S. Air Force installation on the island of Shemya with hurricane-force winds of up to 98 miles per hour, according to the Alaska Daily Dispatch.

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Homes are covered with rocks and mud after debris flows smashed into houses on Dec. 12., in Camarilla, Calif. A day after hitting Northern California, hurricane-force winds traveled down the coast to hit the drenched Southern California region.

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