Strange sea level rise along East Coast this summer

By Beth Daley, Globe Staff

You probably didn’t notice it sitting on the beach this June and early July but tides in New England were as much as a foot higher than predicted.

The unusual phenomena, brought on by a rare combination of persistent Northeast winds and a weakened ocean current, highlights a growing body of research by scientists about sea level variation from one region to another. Such differences are important to understand as sea levels rise from warming ocean waters and melting glaciers.

Chatham homes succumbing to the sea in early summer. (Globe photo/Vincent DeWitt)

“It averaged six inches higher (in the Boston area) during the peak in early July and was as much as a foot higher in Cape Cod,’’ said Mike Szabados, director of NOAA’s Center for Operational Oceanographic Products and Services. “The ocean is dynamic and it’s not uncommon to have anomalies….What made this event unique was its breadth, intensity and duration.”

NOAA scientists observed water levels six inches to two feet higher from Maine to Florida, with the greatest change in sea level – up to two feet – recorded in Baltimore and other Mid-Atlantic areas.

After analyzing data from tide stations and buoys from Maine to Florida, the scientists found that a weakening of an oceanic current that feeds into the Gulf Stream along with steady Northeast winds contributed to the tides. The weakening was greatest in the Mid-Atlantic, which is why tides were highest there.

Amplifying the tides – and leading to minor flooding in some areas - was a perigean spring tide, the time during the spring tide when the moon is closest to the earth and its gravitational pull raises water levels. While the tides were strong, they still pale in comparison to what occurs during a Northeaster.

The scientists say much more work needs to be done to truly understand what is driving geographical changes in tides.

“The report is a good first assessment,” said NOAA Oceanographer William Sweet. But, he added “further analysis is needed to fully understand what is driving the patterns we observed.”

For the full report go to
http://tidesandcurrents.noaa.gov/publications/EastCoastSeaLevelAnomaly_2009.pdf