The derecho (fast-moving band of severe thunderstorms) that clobbered the Northeast on June 13 was nothing terribly special by National Weather Service standards; meteorologists classified it as “low-end.” But the storm’s aftereffects—kicking up six-foot waves in more than 30 tidal gauges along the East Coast—spurred a more elusive natural phenomenon: a tsunami.
Well, maybe not exactly a tsunami. Paul Whitmore, director of the National Oceanic and Atmospheric Administration Center For Tsunami Research, explained that the wave was probably just a “meteotsunami”—caused by meteorological conditions, not seismic activity. The derecho system that moved through the Northeast might have changed the air pressure just enough to “generate waves that act like tsunamis,” Whitmore said.
The tsunami’s cause is still under review: the West Coast and Alaska Tsunami Warning Center says it could be anything from the strong storm to the continental shelf east of New Jersey slumping. Typically in tsunamis, water moves out to sea and rapidly rushes back in, but water speeds reported in Rhode Island indicated something other than a storm surge.
The tsunami (for now) wave peaked at just under a foot above sea level at a tide gauge in Newport, Rhode Island, and NOAA tracked the tsunami signal from Massachussets down to North Carolina; reports came in from as far as Puerto Rico and the Bahamas. An eyewitness account from a spear fisherman on the Jersey Shore, Brian Coen, noted an approximately 6-foot wave exposing rocks that were typically submerged in three or four feet of water.
True tsunamis, Japanese for “harbor wave,” are generated by sudden shifts in the seafloor, landslides, or volcanic activity. The last significant meteotsunamis to hit the East Coast occurred in 1992 in Daytona Beach, Florida and 2008 in Boothbay Harbor, Maine. There’s dispute whether an East Coast derecho at the end of June in 2012 stirred up a meteotsunami in the Chesapeake Bay—waves reportedly only reached 40 centimeters.