The type of storm that hit New England hard early Monday morning and knocked out power to nearly half a million Mainers is an unusual meteorological event sometimes referred to as a “bomb cyclone.”
The unusual, “Sharknado”-like nickname stems from from a phenomenon called “bombogenesis,” in which atmospheric pressure drops relatively quickly (technically, 24 millibars in 24 hours), whipping up the kind of sudden strong winds that toppled countless trees throughout the region late Sunday and on Monday. More than 80,000 customers of Maine’s two largest electricity utilities still did not have power as of Friday morning.
Monday’s tempest was not a named storm, though the remnants of Tropical Storm Philippe did play a key role in its development as it merged with a cold front that was moving eastward from the Midwest over the weekend. As Philippe, a relatively weak and poorly organized cyclone, moved northeast over south Florida toward the mid-Atlantic, its tropical moisture fed the intensity of the advancing cold front, causing the rapid drop in air pressure and resulting powerful winds.
— NWS Caribou (@NWSCaribou) October 30, 2017
“It took place right over New England,” said Tom Hawley, a forecaster with the National Weather Service in Gray. “If Philippe wasn’t there, we still would have had a fairly [strong] storm.”
Bombogenesis usually is associated with winter nor’easter storms, Hawley said, estimating that the phenomenon occurs in New England maybe once a year. All storms, including cyclones and blizzards, involve drops in atmospheric pressure but most do not fall rapidly enough to be characterized as bombogenesis. When the phenomenon does occur, the storms that result are called “bomb cyclones,” according to the National Ocean Service.
The storm that blasted its way through New England was complex, Hawley said. It retained much of its counter-clockwise cyclonic rotation as far north as the islands off Cape Cod, which contributed to the wind speeds that pummeled the Maine coast, which was to the east of the storm’s center. Wind speeds were even faster at higher elevations, which is why a gust of 131 mph — in the range of a category 4 hurricane — was recorded Monday morning at the 6,288-foot summit elevation of Mount Washington in neighboring New Hampshire, he said.
— NWS Gray (@NWSGray) October 30, 2017
Most of the damage occurred at lower elevations, with flash floods in western Maine and nearby states and high winds throughout Maine — including some hurricane-level gusts above 73 miles per hour. Some parts of western Maine, and many areas in New Hampshire, received upwards of two inches of rain Sunday night and Monday morning, while a handful of locations in both states topped 5 inches over the same time period.
A weather buoy at Matinicus Rock in the Gulf of Maine recorded a wind gust of 92 mph while another at Isle of Shoals, which sits in the gulf at the Maine-New Hampshire border, recorded a wind gust of 82 mph, according to the National Weather Service. A weather buoy near Mount Desert Rock recorded a 75 mph wind gust.
On land, many gusts around 60 mph were recorded, well within the range for tropical storm-force winds. Portland’s jetport had a top wind gust of 69 mph in the hours before sunrise Monday, while in Bangor it hit 66 miles per hour. Augusta and Portsmouth, N.H., also had top wind gusts in the 60s.
Peter Rogers, acting director of the Maine Emergency Management Agency, said Tuesday that persistent drought conditions in Maine may have contributed to the number of trees that blew over, many of them damaging power lines, homes and vehicles. Foliage also is a factor that adds to the pull on trees and increases the likelihood they will topple when hit by powerful winds.
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