Did a tsunami hit Maine?

A couple of folks posting comments to recent entries have asked about what happened in Maine the afternoon of October 28, when several huge anomalous waves suddenly surged onshore. Indeed, it was a very curious and interesting case!

From this article in The Boston Globe:

>>>
Dockworker Marcy Ingall saw a giant wave in the distance last Tuesday afternoon and stopped in her tracks. It was an hour before low tide in Maine's Boothbay Harbor, yet without warning, the muddy harbor floor suddenly filled with rushing, swirling water.

In 15 minutes, the water rose 12 feet, then receded. And then it happened again. It occurred three times, she said, each time ripping apart docks and splitting wooden pilings.

"It was bizarre," said Ingall, a lifelong resident of the area. "Everybody was like, 'Oh my God, is this the end?' "

...

Residents and business owners in Boothbay said they were glad the phenomenon didn't happen at high tide, when it might have caused massive flooding and more extensive damage. Janice Newell, who lives nearby in Head of the Harbor, told the local newspaper the rushing water "was of biblical proportion."

"There were three large whirlpools in the inner harbor, up to within a foot of my neighbor's wall," she told the Boothbay Register. "It was beautiful, but it was scary."

Elena Smith, a waitress and part-owner of McSeagull's restaurant overlooking the harbor, said the late-afternoon lunch crowd sat speechless as the waters rose and receded. She was stunned to see the normally safe and placid harbor suddenly run like rapids. Some residents reported seeing massive whirlpools of water that disappeared, leaving clam shells and seaweed in vortex patterns on the harbor floor.

"It felt like somebody took the plug out somewhere" in the ocean, Smith said. "It felt like there must have been water missing in the ocean someplace."
>>>

This was the meteorological setup that afternoon:

The big, unusually-early snowstorm I wrote about at the time was in progress over the interior Northeast.

Eventually stronger winds and higher waves circulating around from the west and south sides of the cyclone (where the "pressure gradient" was tighter) made it to the Maine coast, but were not present at mid-afternoon when the strange event occurred.

The 3pm EDT (19 UTC) observation at this buoy just offshore of the area on the coast which was hit shows winds of 7 meters per second (~16 mph) with gusts to only 8 m/s (18 mph), and significant wave heights of only 1.2 meters (4 feet).

Here's the official statement from the National Weather Service:

The Globe article goes into additional detail, including referencing the possibility of the culprit being a "squall line surge" like one which hit Daytona Beach 16 years ago. As this section of the book Coastal Processes with Engineering Applications states, "squall line surges are caused by the movement of a relatively small atmospheric pressure perturbation at the approximate speed of the waves generated."

It then describes the 1992 event: "On the evening of July 3, 1992, at Daytona Beach, Florida, a freak wave about 2 m high surged up on the beach on an otherwise calm night. ... Observers soon reported a sudden increase in wind speed occurred with the change from a warm and humid evening to cool and windy conditions. Later, radar images demonstrated that a squall originated offshore of Georgia and moved south first along the Georgia and later the Florida coast ..."

A NOAA satellite image from that evening around the time the wave hit depicts a band of clouds curving in a gigantic backward S all the way from Hudson Bay to the southeast U.S. and on into the Atlantic, including a line of showers and thunderstorms near the northeast Florida coast. Radar showed that about 20 minutes before the ocean wave reached the northern Daytona Beach area and proceeded southward, there was a cluster of thunderstorms which had moved south from the Georgia coast; the storms then dissipated.

Those radar analyses are from the definitive meteorological analysis of that event, this paper published in the Bulletin of the American Meteorological Society, which concluded that "analysis of tide gauge and atmospheric data strongly suggests the water wave was generated by a squall line." (An interesting account of how a meteorite had been suspected is on pages 46-62 of this magazine.)

With the Maine event, there was that potent system in the Northeast, which at the time was swinging a band of locally heavy rain across northern New England:

[Image source: GRLevelX]

However, the band had already passed through Boothbay Harbor and thereabouts, and the buoy observations above gave no indication of a significant change in weather or water parameters when it came through there around 2pm EDT (18 UTC).

Thus (and having discussed with TWC's wave expert, Dr. Steve Lyons), there's nothing weatherwise which jumps out as having been the cause, suggesting that the "rogue" wave may have been a tsunami rather than something meteorological. That's based on this quick perusal of the data as opposed to an exhaustive investigation; more study would be necessary for a conclusive determination, although as the NWS notes we may never know for sure exactly what happened. The only earthquakes in the Atlantic that day were many hours earlier, very small, and far away near Puerto Rico. The process of elimination suggests that if weather or earthquakes were not the cause maybe it was an underwater slumping/landslide, but it'd be difficult to precisely determine that.

This report which includes the history of Maine tsunamis indicates that there have been two other tsunami events recorded in the state, in 1872 and 1926. (In regard to that article, note that tsunami is the proper term, not tidal wave.)

Whatever took place this time, it was much more subtle compared to the other extreme. On July 9, 1958 on the shore of Lituya Bay, Alaska, after an earthquake-generated landslide plunged into the water of Gilbert Inlet, a local tsunami reached a height on land which was reported to be as high as 1720 feet above sea level!