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Center for Operational Oceanographic Products and Services

What are El Niño and La Niña?

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NOAA Study May Help East Coast Prepare for El Niño Years

July 19, 2011
coastal North Carolina

Fifty-three percent of our nation's total population currently lives in coastal counties and by 2020, the population in those areas is expected to increase by eight percent. Given our affinity for the coast, it is important that we are prepared for potential coastal hazards.

NOAA Study May Help East Coast Prepare for El Niño Years

Coastal communities along the U.S. East Coast may be at risk of higher sea levels accompanied by more destructive storm surges during future El Niño years, according to a new NOAA study published in the Monthly Weather Review, a journal of the American Meteorological Society (AMS).

AMS Director Keith L. Seitter says of the study, “This research furthers our understanding of the interconnections between the ocean and atmosphere, which are so important in the Earth’s climate system, and points to ways to help coastal communities prepare for the winter season.”

What is an El Niño?

Principal investigator Bill Sweet, PhD, an oceanographer at NOAA’s Center for Operational Oceanographic Products and Services, explains that an El Niño – a weather phenomenon that most people associate with the West Coast – is characterized by unusually warm ocean temperatures in the Equatorial Pacific that normally peak during the “cool season” (October to April) in the Northern Hemisphere. El Niños occur every three to five years, with especially strong events occurring about once a decade.

“El Niños have important consequences for global weather patterns, often causing wetter than average conditions and cooler than normal temperatures across much of the central and southern United States,” Sweet says.

50 Years of Data

Prompted by the highly active El Niño of 2009-10, Sweet and his colleague Chris Zervas reviewed 50 years of data on cool-season water levels and storm surges at four East Coast sites: Boston, Massachusetts; Atlantic City, New Jersey; Norfolk, Virginia; and Charleston, South Carolina. A storm surge is defined as a rise in coastal sea level of one foot or greater.

Sweet and Zervas discovered that between 1961 and 2010, the average number of storm surges nearly tripled at the sample sites during strong El Niño years. Additionally, the sites experienced an average four-inch elevation in mean sea level above predicted conditions.

El Niño, Nor’easters, and La Niña

The study builds on previous ocean-atmospheric research which concluded that those classic (and dreaded) ‘Nor’easters’ –  storms with gale-force winds that blow in from the northeast – are more frequent along much of the East Coast during cooler El Niño months. El Niño and its impacts usually fade during warmer months, and often transition into a La Niña, during which eastern Pacific surface waters cool down and cause weather conditions generally opposite to those of El Niño.

“High-water events are already a concern for coastal communities. Studies like this may better prepare local officials who plan for, and respond to, these conditions in their communities,” Sweet concludes.