The bomb cyclone that’s swamped the Eastern Seaboard with a trifecta of snow, hurricane-level winds, and cold had an extra-nasty surprise for Boston on Thursday, as the city and its surrounding coastal areas were hit with unprecedented flooding, with meteorologists predicting it would smash a nearly 40-year record.
The main culprit of Boston’s frozen slushie flood, though, is a surprising one: last month’s supermoon.
Benjamin Sipprell, a meteorologist in Boston for the National Oceanic and Atmospheric Administration, told The Daily Beast that the blizzard, combined with Thursday’s high tide between noon and 1 p.m. EST—plus the extraordinary lunar event last month—meant that a flood was poised to take place.
“Leading up to the tide, we had hurricane-force winds and 20-foot waves on coasts facing the Atlantic,” Sipprell said. “There was a 2- to 3-foot surge that got driven into inner bays and inundated a lot of infrastructure, roads, and basements into Nantucket.”
The result was catastrophic, with officials warning residents to stay off streets as the frigid temperatures would ice the water over and freeze vehicles to their locations. Thousands of Bostonians were without power on Thursday night, as wind chill temperatures sank into the deep freeze.
Sipprell described a scene that seemed practically apocalyptic: “Cars floating away, other debris floating away, water in basements,” he ticked off. NOAA has kept meteorological records since 1921, and Sipprell said preliminary measurements indicated that Thursday’s high tide surpassed the record of 15.1 feet in Boston during a 1978 blizzard by at least a tenth of an inch.
That’s gigantic, the sort of tide that goes down as legend in Boston. “Normal tides in Boston are between 9 and 10 feet,” Sipprell explained. “When we get tides, we get some that go up to 12 feet or more. We were forecasting 12.1 feet with this one, but with the surge, it got bumped up to 15 feet.
“It’s definitely historic.”
The towering tide was thanks to the supermoon on Dec. 3. Normal full moons happen any time on the elliptical path of the lunar orbit, but when the full moon occurs right at the tip of the orbit closest to the Earth—what astronomers refer to as the perigee—the moon appears at its largest and brightest, earning it the superlative moniker of supermoon. And given that a full moon’s gravitational pull brings tides up higher than normal, the supermoon’s closeness to Earth magnified this effect to a detrimental degree in Boston.
That said, Sipprell isn’t giving the moon all the credit. “The storm was the biggest thing of all,” he noted. “The combination of the Arctic air mass surging south and the subtropical air mass going north [along with] the massive deepening low [pressure] means that we were going to deal with coastal flooding.”
Sipprell further noted that the normal “rule of thumb” with a textbook “bombogenesis”—the type of storm the East Coast was hit with on Thursday—is that pressure falls, or deepens, 24 millibars in 24 hours. “We were well over 50 [millibars] over the last 24 hours,” Sipprell said, saying that as the storm moved off the coast of Florida, it went from a 1,000 millibar low pressure system to 950 millibars by the time it hit Maine—a drastic nosedive that accentuated the disastrous effects of the high tide and storm surge in Boston. Sipprell likens the pressure fall to that of an accordion: There’s lots of air when it’s spread wide, but as it comes together (and makes music), it pushes the air out.
Richard Alley, a glaciologist at Penn State, said climate change is also to blame for the destructive flooding Boston is dealing with right now. “Sea level has been rising because of human-caused warming,” he told The Daily Beast via email. “Most of the high water in Boston and elsewhere along the East Coast is from the wind, but a little bit of extra flooding can be traced to the ocean starting out higher that it was in the past.” Higher waters mean a smaller trigger to push an otherwise serene bay into ferocious flood.
And while a blizzard might push any thoughts of “global warming” out of the way, Alley said it certainly has a role to play for the higher than normal sea levels outside Boston. “The Atlantic has been running on the warm side, in part because of human-caused warming, which gives more energy that can contribute to stronger storms,” he pointed out. “And, there is a fascinating although as yet unproven idea that the rapid warming that has been observed in the Arctic has affected the circulation in ways that make cold outbreaks such as this one more likely or more persistent, shifting the cold air down here and then having it linger.”
For Sipprell, the immediate plan was to forge a path home. With flooded streets teeming with ice chunks and electricity down across the city, he wasn’t exactly sure how. “I’ll have to get home somehow,” he chuckled.