While Dorian was pulling away from the United States on Saturday night, parts of the Canadian Maritimes were getting battered with 100-mph wind gusts. But Dorian’s most terrifying feat in Canada may not have struck on land. Dorian whipped up a 100-foot rogue wave.
A 100-foot wave is taller than an eight-story office building.
Readings like this are virtually unheard of, for obvious reasons. But Bill Carter, director of the Center of Applied Ocean Technology at the Marine Institute, confirms the buoy was calibrated and operating correctly.
“I make sure the equipment’s working, which it was,” said Carter. He explained that the 100-foot figure indeed measures an individual wave crest to trough.
“Only 10 minutes of the data from every hour is sent back to shore,” said Carter, citing costs for telemetering the data wirelessly to land. “There could have been even higher waves during the other 50 minutes. We’ll only know when we get the data off the buoy.”
Winds at the time were rough, but not terribly ferocious. They were clocked as high as 66.2 mph, although there’s a more than 80 percent chance they gusted higher, because we only “see” 10 minutes’ worth of data from every hour.
The rogue wave occurred within the storm’s dry slot, meaning it wasn’t even raining. But a developing wind maximum associated with Dorian’s transition into a nontropical system, known technically as a sting jet, upwind probably added to the force of the winds to the west, agitating the waters in the vicinity even more.
The buoy, moored two miles offshore, sits in about 160 feet of water normally. That’s not very deep, especially for a shallow-water wave to reach 100 feet. However, theoretical maximum height-to-depth ratios have been demonstrably proved in the past to range between 0.55 and 0.8, meaning that an 88- to 125-foot wave is possible. The upper bounds were extremely difficult to simulate under laboratory circumstances, but it indicates a 100-foot wave is certainly not out of the realm of possibilities.
Brian Walsh is a meteorologist at PAL Aerospace in St. John’s. He’s confident that the 100-foot reading is legitimate.
“The fact that there were other reports of 26+ metre (85 foot) maximum wave heights leads me to believe it could be possible,” wrote Walsh.
One additional figure we can turn to is the significant wave height. It’s the average of the tallest one-third of all the waves. The National Weather Service Ocean Prediction Center did analyze a small area of 50-foot significant wave heights Saturday night. Individual waves may be twice the significant wave height. Albeit an extremely low-probability event, these top-tier 100 footers wouldn’t be impossible under that scenario.
A number of other stations nearby also reported significant wave heights of 50 feet or more.
Canadian buoy #44137, located south of Nova Scotia near Sable Island Bank, is reporting a significant wave height of 50 feet thanks to #HurricaneDorian. This buoy infamously reported a 100.7 foot wave during "The Perfect Storm" in October 1991. @rms5539 pic.twitter.com/UpMhvZHuJI— Simon Lee (@SimonLeeWx) September 7, 2019
However, there are upper bounds as to how open-water waves can grow in different environments. Given how relatively close this measurement was recorded to shore, odds are that this wave may have been helped along by two processes: bathymetry and interference.
Bathymetry describes the slope, topography and elevation of the sea floor/continental shelf. That can have a role in forcing waves to ride upward, causing waves to diffract, or otherwise affecting the propagation of waves.
“The Cabot Straits bathymetry is varied, with the Laurentian Channel creating a deep trench through its metre
,” explained Walsh, “and comparatively shallow coastal waters closer to Newfoundland and Cape Breton Island.” While these conditions are impossible to validate, Walsh said that these conditions have been known to foster the development of these rare rogue waves before.
Interference could play a role as well. That means that several ordinary waves may have combined constructively, their amplitudes piggybacking to form one mammoth wave. Research has shown that waves intercepting one another at an angle can have this effect, with the “sweet spot” of a 120-degree intersection achieving the tallest waves.
Rogue waves have been the subject of folklore and fascination for years. It has long been rumored that a mythical — albeit possible — string of three rogue waves dubbed the “three sisters” abruptly swallowed the SS Edmund Fitzgerald during a storm on Lake Superior on Nov. 10, 1975. All 29 crew aboard perished, the ship vanishing without a trace. The cause of the disaster is still not known.
Rogue waves largely remained an old sailor’s tale until 1995, when what was before legend suddenly was proved a scientific reality. An oil rig in the North Sea off the coast of Norway was suddenly broadsided by an 84-foot wave on New Year’s Day in 1995. It was dubbed the “Draupner Wave,” because it slammed the Draupner E drilling platform owned by Statoil.
What happened Saturday night off Newfoundland? We may never know for sure. But one thing is certain.
We’re going to need a bigger boat.
Seems like a peculiar location, with very steep slope of the seafloor. Looking at the timing, this very large Hmax value (as "real" as Hmax measurements get...), is possibly caused by the interaction of 2+ wave fronts, and not an "open ocean + deepwater" wave. pic.twitter.com/y0MqS6mKjH— Rémi C2W (@remi_wnd) September 9, 2019
The way things are looking I'm not surprised. It hasn't even fully hit yet and it's already pretty wild here— Matt Cooper (@matt_cooper67) September 7, 2019