What the National Weather Service initially called a weather-related meteotsunami off the coast of the Jersey Shore and Delaware during severe storms Tuesday afternoon actually wasn't a tsunami after all because it didn't go far enough.
"A meteotsunami, like all tsunamis, is a propagating wave train," said said U.S. NWS Pacific Tsunami Warning Center in a Facebook update. "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 peak of the event occurred right around 3:15 p.m. Eastern Standard Time and caused water levels to drop to around 0.5 meters, said the Honolulu, Hawaii-based Tsunami Warning Center.
So what’s a meteotsunami?
"A meteotsunami is generated when a high-speed straight-line windstorm (usually called a de recho) passes over shallow water," wrote the Tsunami Warning Center on Facebook. "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."
A similar meteotsunami along the Jersey Coast in 2013 impacted coastlines up and down the East Coast.
This time the incident, which the National Weather Service said was part of an "interesting" weather day, didn't make significant landfall.
"The waveform in the figure may simply be the result of wind piling up water down Delaware Bay," said the NWS. "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."
Click here for more about potentially dangerous meteotsunamis.