It was the day of the derecho (for places like Pennsylvania, Maryland, and New Jersey--the derecho having passed over Chicago and most of Ohio the night prior). It moved off shore in the morning and early afternoon hours and the pressure differential caused tsunami-like waves to propagate away from it as the derecho barreled its way into the North Atlantic. This is known as a meteotsunami.
Tsunamis and meteotsunamis propagate in the water in the same way and have the same coastal dynamics. In other words, for an observer on the coast where it strikes the two types would look the same. The difference is in their source only. One definition of a meteotsunami is as an atmospherically generated large amplitude seiche oscillation.NBC 10 in Philadelphia reports today, almost two weeks later:
This event produced a tsunami that was recorded at tide gages monitored by the West Coast/Alaska Tsunami Warning Center (WCATWC),” they said. "The tsunami was observed at over 30 tide gages and one DART buoy throughout the Northwestern Atlantic Ocean."Those waves then struck the Jersey Shore. One of the group owners of this facebook group had to send the tide data to NOAA for them to look into it. He reports, as the waves made landfall at Barnegat Light north of Atlantic City around 330pm, eastern, on the 13th:
Officials say the source of the tsunami is “complex” and “still under a review.” They also say however that the earlier storm system that struck the area was a possible cause.
"The event occurred in close conjunction with a weather system labeled by the National Weather Service as a low-end derecho which propagated from west to east over the New Jersey shore just before the tsunami," they wrote.
Around 3:30pm on Thursday June 13, 2013, Brian Coen was spear fishing near the mouth of Barnegat Inlet; just south of the submerged northern breakwater. Earlier in the day around noon, thunderstorms had moved through the area. By 3:30pm the weather was overcast with a light east wind. At approximately 3:30, 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.Here is another account.
At this point, Brian noticed a large wave coming in, approximately 6 feet peak-to-trough and spanning across the inlet. The upper 2 feet of the wave was breaking. This wave occurred in conjunction with a reversal of the current such that even though the tide was going out, a strong surge was entering the inlet. This surge carried the divers back over the submerged reef and into the inlet from where they were picked up. On the south jetty three people were swept off the rocks which were 5 to 6 feet above sea level at the time. At least two were injured requiring medical treatment. There was no more strong activity after about 5 minutes
Pretty fascinating, eh?
After striking the Jersey Shore (the wave's first landfall appears to be in Lewes, DE, south of the mouth of Delaware Bay) it then propagated into New York Harbor, Long Island Sound, Massachusetts and beyond. It struck Bermuda before it propagated into the Chesapeake although there may have been a separate event in the Chesapeake earlier in the day as the derecho passed that morning. The continental shelf will slow a tsunami wave down. It even dinged a DART Buoy east of Atlantic City. DART buoys are an essential part of any tsunami warning system so consider that good news. NOAA drills tsunami on the East Coast pretty much every March. We just got a real world test that the system is functional.
You can explore the data set curated by NOAA and the West Coast Tsunami Warning Center here.
The WCTWC seems to think some slumping at the continental shelf may have been involved. I'd tend to agree. I'm not quite sure if meteotsunami can propagate the distances that this one did (Bermuda and locations on the north coast of Puerto Rico all noted the tsunami.) One of the East Coast's more under-appreciated hazards is the fact that the continental shelf lip is extremely unstable. Up and down the East Coast there are scars that mark the locations of past landslides of debris and sediment down the continental shelf. Research continues to be done, and I've written about it in the past. Underwater landslide tsunami have happened before in the east, most notably in 1929, although that was triggered by an Mw7.2 earthquake.
All in all, an interesting event. A couple people were injured---meteotsunami (if that's just what this was) can be dangerous, even deadly.
I just thought this was too interesting not to share. Thanks for reading