Metro

There was a meteotsunami last night off the coast. What’s that?

This graphic shows the predicted tide and actual tide measurements at New Haven, Connecticut, and Woods Hole.
This graphic shows the predicted tide and actual tide measurements at New Haven, Connecticut, and Woods Hole.

The thunderstorms that swept through Southern New England on Tuesday, hurling hail and dumping rain, also stirred up the waters off the coast as they raced out to sea, causing a phenomenon known as a meteotsunami, the National Weather Service said.

While tsunamis are large waves triggered by earthquakes, meteotsunamis are waves caused by air pressure disturbances often associated with fast-moving storms, such as squall lines or thunderstorms, according to the National Oceanic and Atmospheric Administration.

At 9:21 p.m. Tuesday, the National Weather Service Boston office warned that air pressure sensor and tide gauge readings off the coast “indicated that a weather-generated abnormal rise” in water levels had been “triggered by a storm system as it moved over the ocean. Water level fluctuations of several inches to one foot above normal tide in localized areas can be expected for the next several hours as a series of surges strike the coast.”

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The forecasters said no coastal flooding was expected, but the strong currents associated with the surges could pose a danger to people in or near the water. They warned of effects along the south coast of Massachusetts and Rhode Island.

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Alan Dunham, a meteorologist with the weather service, there were no reports of damage or any other trouble from the weather event Tuesday night.

“These are very small events that have very little impact,” said Dunham. He said it was the first time he had seen one in more than two decades with the weather service in the area.

The Weather Service noted that meteotsunamis are different from storm surge, which happens when strong winds push water ashore, causing water to steadily rise, a common phenomenon during coastal storms in New England.

In the United States, the best conditions for meteotsunamis, which research indicates are more common than previously thought, are along the East Coast, the Gulf of Mexico, and in the Great Lakes, the weather service said.

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Recent East Coast meteotsunamis include one in June 2013 where, on a clear, calm day, waves crashed upon the coasts of southern Massachusetts and New Jersey, where three people were injured and an October 2008 incident in Boothbay Harbor, Maine, when a series of waves up to 12 feet high damaged boats and shoreline infrastructure, the weather service said.

Tide gauges reflected the meteotsunami as far south as Delaware, the Washington Post reported.

This buoy south of Long Island also apparently recorded the phenomenon, the weather service said.