A “bomb cyclone”—a meteorological phenomenon that describes a storm with plummeting atmospheric pressure—struck the Upper Cape late Wednesday night, October 16, and early Thursday morning, October 17, bringing down trees, branches and wires and cutting power to more than 36,000 Eversource customers.

There were more than 83,000 power outages across the Cape and the Islands, the Eversource outage map said.

Around 6 AM there were 1,900 customers without power in Sandwich, based on numbers provided by Eversource. That number went down to 628 an hour later, but jumped back up to 2,464 homes by 11:30 AM. East Sandwich was the most impacted by the power outages.

While Sandwich schools retained power, superintendent Pamela A. Gould called parents shortly after 6 AM to inform them of the two-hour delay.

“We are going to operate with a two-hour delay in an effort to maybe allow some power to come back, but to also give you a bit more time this morning to get everyone ready without the power,” she said.

She said that students unable to make it in will not be penalized, but that the schools having power means that students will be warm and have the ability to eat a hot lunch.

During the storm, wind gusts up to 80 miles per hour and rains of more than two inches prompted Falmouth Public Schools and Sturgis Public Charter School in Hyannis to call off classes.

Director of Natural Resources David J. DeConto said that since the storm’s winds came out of the south and southeast, the Sandwich coastline does not appear to have suffered any damage from the two storms the area has been affected by over the past two weeks. Towns such as Falmouth, whose coastline faces more south, took a much harder hit from the storm.

“We will continue to check out the coastline after the wind dies down later tonight and tomorrow,” Mr. DeConto said.

Of the four Upper Cape towns, Falmouth endured the most damage, with numerous impassable roads and detours, sources said. Falmouth Hospital was running on generators Thursday, a spokesman for the Barnstable County Regional Emergency Planning Committee said.

The National Weather Service announced a high wind warning for the Cape until 6 PM Thursday, with southwest winds between 25 to 35 miles per hour and gusts between 50 and 60 miles per hour.

Charles Orloff of Mashpee, executive director of the Blue Hill Observatory and Science Center, said this was a rare storm with an extreme, ear-popping pressure drop.

“With a bomb cyclone, you have a 30-millibar drop in 24 hours. This one had a 43-millibar drop in 24 hours. You very seldom see that. It just went bombing away,” he said.

The bomb cyclone, which had moved up the east coast, joined with a cold air system coming out of Canada.

“The low-level jet stream at about 5,000 feet became very strong and combined with heavy rain dragged down the heavy winds from higher altitudes,” Mr. Orloff said. “I heard reports of 100-mile-per-hour gusts in Truro, but those were unofficial reports and totally bogus.”

More representative and reliable wind speeds came from the rooftop equipment at Menauhant Yacht Club in East Falmouth, which showed the highest gusts at 69 miles per hour, Mr. Orloff said.

“There were winds of 70 to 75 miles per hour on most parts of the Cape—80 at most, hurricane-force—and based on the fact that it all occurred about the same time with a 10-minute spike or peak around 3 AM, the highest gusts might have lasted less than 1 to 3 seconds. It was that peak that brought down the branches and wires,” he said. “The National Weather Service is still reviewing the data.”

Also contributing to the strength of the storm and the resulting damage were the weight of leaves on the branches as well as the suddenness of the winds, which were blowing east-northeast at the peak, Mr. Orloff said.

“We went from very little wind to tremendous wind. We also had two inches of rain from a storm less than a week ago, so the ground is now soft and very wet,” he said. “The center of the storm went a little bit west of us, but I wouldn’t be surprised if it went a little more southeast.”

At Blue Hills Observatory in Milton, meteorologists recorded the lowest atmospheric pressure in 134 years of keeping records in the month of October, and the readings were similar on Cape Cod, Mr. Orloff said.

“The pressure was 28.81 inches at Blue Hill, which was the same as at my house in Mashpee at 4 AM,” he said. “Normal pressure is around 30 or 31 inches. It’s never below 29 inches.”

Ferry traffic from Woods Hole to Martha’s Vineyard has also been strongly impacted, the Steamship Authority said.

“All trips for the M/V Iyanough were canceled Thursday. All service on the Vineyard route was canceled until and including the scheduled 2:50 PM departures of the M/V Governor and M/V Katama,” the Steamship Authority said. “Additionally, Friday, October 18, will be a reservation-only day on the Vineyard route. There will be no standby travel on the Vineyard route.”

There was a slight chance of showers before 9 PM Thursday, with mostly cloudy skies and a low temperature around 45 degrees, a west wind between 10 to 18 miles per hour and gusts as high as 33 miles per hour. Friday’s weather will be partly sunny, with a high near 58 degrees, a northwest wind 11 to 15 miles per hour and gusts as high as 25 miles per hour.

“Intense low pressure over central New Hampshire will continue to slowly pull away. However, the intense pressure gradient between departing low pressure and high pressure to the west will create an increase in winds during the day Thursday,” the Barnstable County Regional Emergency Planning Committee wrote in a release. “Eversource is in the process of cutting and clearing, restoring and doing damage assessment.”

No regional emergency shelter system activation is planned at this time, but the committee said it would continue to assess the situation.

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