The low-end derecho that pushed from Chicago to Washington, D.C., on June 13 may have sparked a meteotsunami on the New Jersey coast, said Paul Whitmore, Director of the Tsunami Warning Center.
"The first impulse was to see this as meteorologically driven, but once a system gets over the shelf cloud, we lose data," he said. "It makes it hard to confirm."
It could take months before the event is officially confirmed one way or the other, but it seems likely at this time that the derecho may have caused the tsunami-like waves.
Animation of the storm track by the National Oceanic and Atmospheric Association
A meteotsunami differs from a tsunami because it is caused by a weather event rather than by seismic activity. Most tsunamis are created by volcanic eruptions or earthquakes, which gives researchers a fixed point to work off of. When the waves are created by a weather event like a derecho, it requires more, exact elements to come together for its creation. These elements are harder to track because they are occurring above the Earth's surface.
Tsunamis and meteotsunamis are more than just large waves; wave frequency and speed are more emphasized factors in labeling a tsunami. So far, the waves that hit New Jersey seem to be in line with the qualifications for a meteotsunami.
The waves were first spotted June 13 by Brian Cohen, who was out spear fishing in the Barnegat Inlet in Ocean County when he saw waves that were approximately 6 feet peak-to-trough spanning across the inlet.
According to an account posted to the Tsunami Warning Center:
"Earlier in the day around noon, thunderstorms had moved through the area. By 3:30 p.m. [EDT] the weather was overcast with a light east wind. At approximately 3:30 [p.m. EDT], the outgoing tide was amplified by strong currents which carried divers over the submerged breakwater (normally 3-4 feet deep). This strong outrush continued for 1-2 minutes and eventually the rocks in the submerged breakwater were exposed. Brian backed his boat out before being sucked over as well."
At over 30 gauges the indications were recorded for a tsunami in its strength and wave frequencies. According to Whitmore, shelf clouds off the New Jersey coast are conducive to such events occurring.