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June 23, 2016

NWS: Actually, 'meteotsunami' did not strike off coast of Jersey Shore, Delaware

Events can produce ocean waves as fast as overhead weather system

UPDATE (6/23/16): The U.S. National Weather Service Pacific Tsunami Warning Center has walked back an initial graph analysis that led them to conclude a meteostunami occurred Tuesday afternoon off the coasts of New Jersey and Delaware.

In a correction posted Thursday afternoon on Facebook, the Warning Center clarified that Tuesday's event did not possess all of the same characteristics as a previous meteotsunami that occurred in the area in 2013. 

Here's their explanation: 

A meteotsunami, like all tsunamis, is a propagating wave train. While the sea-level anomaly shown in the figure did show up on other nearby tide gauges, it did not advance far beyond the mouth of Delaware Bay. In particular, it did not reflect from the shelf edge to come back to threaten the coast in the manner of the meteotsunami of June 2013. Since it did not propagate far, we cannot call the event a meteotsunami.

The waveform in the figure may simply be the result of wind piling up water down Delaware Bay. It clearly was a weather-induced long-wavelength phenomenon, but, unlike 2013, those waves were not the result of Proudman Resonance across the continental shelf (the atmospheric pressure record from Cape May shows a broad pressure pulse coincident with the waves rather than what was seen in 2013: a pressure pulse preceding the waves by more than an hour). The source area of this event appears to have been too small to sustain a tsunami; the waves rapidly dissipated.

Nevertheless, yesterday was interesting!

Yes, and now we all know what a meteotsunami is and is not. 

Residents along the New Jersey coastline may not have felt a rumble on Tuesday, but the U.S. National Weather Service Pacific Tsunami Warning Center confirmed that an event known as a "meteotsunanmi" occurred off the beaches of New Jersey and Delaware.

The Tsunami Warning Center posted the following message Tuesday afternoon on Facebook .

Naturally, anything containing the word "tsunami" raises eyebrows after the catastrophic events in Indonesia, Chile and Japan. In the latter two cases, the tsunamis were precipitated by major earthquakes.

Here's how the NWS describes a meteotsunami:

"To explain: a meteotsunami is generated when a high-speed straight-line windstorm (usually called a de recho) passes over shallow water. The speed of a tsunami in deep water is hundreds of km per hour, but in shallow water it's much slower. If the water depth is 20 meters (as it is off the mouth of Delaware Bay), the tsunami speed is only 50 km/h. A low-pressure atmospheric system traveling at 50 km/h (or sustained winds of 50 km/h) can therefore kick up a "tsunami" (the process is called Proudman Resonance). So you can get a tsunami-like phenomenon generated not by an earthquake but by weather. We call these things meteotsunamis."

According to the Tsunami Warning Center, a similar meteotsunami happened off the Jersey Shore in 2013. Three people were injured in Barnegat Inlet when a six-foot wave swept them off of a jetty into the water. In some cases, ocean waves can travel as quickly as the atmospheric weather system. The video below shows a model of the impact.

At this point, it's not clear whether any damages have been reported as a result of Tuesday's meteotsunami. Past events around Lake Erie and off the coast of Maine have generated waves as high as ten to twelve feet. While they're difficult to predict, the NOAA has developed improved observational networks and forecast models with an eventual goal of establishing guidelines for meteotsunami warnings.