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Center for Operational Oceanographic Products and Services

Elevated East Coast Sea Level Anomaly: June-July 2009

NOAA's National Water Level Observation Network

Atlantic Oceanographic and Meteorological Laboratory

National Data Buoy Center


NOAA Reports Elevated Sea Levels along Atlantic Coast

In June and July, NOAA scientists discovered elevated sea levels along the entire U.S. East Coast. After observing water levels to 0.15 to 0.61 meters (six inches to two feet) higher than originally predicted, NOAA scientists from the Center for Operational Oceanographic Products and Services (CO-OPS) began analyzing data from select tide stations and buoys from Maine to Florida. They found that a weakening of the Florida Current Transport – an oceanic current that feeds into the Gulf Stream – in addition to steady and persistent Northeast winds, contributed to this anomaly.


The highest sea levels during the event occurred closer to where the anomaly formed in the Mid-Atlantic, where cities like Baltimore, Maryland, at times experienced extreme high tides as much as 0.61 meters (two feet) higher than normal.

In addition to the current and steady winds, elevated water levels in the latter half of June coincided with a perigean-spring tide, an extreme predicted tide when the moon is closest to the Earth during a spring tide. This tidal event added to the observed sea level anomaly, produced minor coastal flooding, and caught the attention of many coastal communities because of the lack of coastal storms during this time that normally cause such anomalies.

“The ocean is dynamic and it’s not uncommon to have anomalies,” said Mike Szabados, CO-OPS director. “What made this event unique was its breadth, intensity, and duration.”

While it is not unusual for smaller regions and estuaries along the East Coast to experience this type of event at this time of year, it is significant that the geographic extent of this event covered the entire East Coast.

The June–July 2009 sea level anomaly is unique because northeast winds along the coast were not at a multi-year high and the Florida Current Transport was not at its low–two factors that can cause elevated sea levels. However, the coupled effect of these two forces created sea levels that were at the highest levels all along the East Coast.

NOAA will work with its academic partners to continue investigating the broader causes behind this event. Further analysis is needed to fully understand what is driving these recently observed patterns.

Findings are published in a NOAA technical report, Elevated East Coast Sea Level Anomaly: June-July 2009.