A “bomb cyclone” that struck parts of British Columbia may look a lot like the hurricanes that hit the Atlantic coast and typhoons that form in the Pacific Northwest, but they are distant cousins at best, scientists say. .
And this particular storm, which left thousands of people in British Columbia without power on Monday, included some unique factors that experts will likely study closely in the coming weeks.
It was a storm that caused widespread power outages in lower continental British Columbia and the Sunshine Coast, causing the cancellation of nearly all ferries in the region. It saw maximum wind speeds of at least 100 kilometers per hour at three locations off Vancouver Island on Sunday.
So how was it different from a hurricane or typhoon?
All of these storms – tornadoes, hurricanes, typhoons, and yes, bomb cyclones – fit into what is known as the “cyclone” family. That’s the broad category name for storms or wind systems that revolve around a low-pressure center.
Hurricanes and typhoons form in subtropical latitudes, toward the equator, in contrast to mid-latitude cyclones, which, in the ocean off the western coast of North America, form in latitudes from northern Mexico to Alaska.
For hurricanes and typhoons, your main driver is the warm waters of the tropics that, together with the winds, create and intensify the low pressure area in the eye of the storm, causing strong and sustained winds.
Mid-latitude cyclones, on the other hand, are created primarily by very strong jet currents, which are obtained when there is a large temperature difference between the pole and the equator. That usually happens in late November and December, when the pole cools down as winter approaches.
“These mid-latitude storms cannot really be compared to the Saffir-Simpson wind scale, where they talk about a category 1, 2, 3, 4 and 5 hurricane, because they talk about sustained winds that we are really just going to see in burst format with the storms that we have in the middle latitudes ”, said Castellan. “Our storms are geographically larger in scale, they have a much larger diameter. Hurricanes are much narrower and smaller, but they are more intense and have sustained winds that are higher. ”
What makes the storm that hit the west coast not just a cyclone but a “bomb” was the rate at which the air pressure dropped in the middle of the cyclone.
To qualify as a “bomb,” the pressure in the cyclone’s eye must drop 24 hectopascals (hPa) over 24 hours. In this storm, those pressures fell from 35 to 40 hPa in 24 hours, said Environment Canada warning readiness meteorologist Armel Castellan of Victoria.
A US buoy off the west coast registered a pressure of 942.5 hPa on Sunday, the lowest pressure ever recorded in the region.
While its extreme pressure drop, and the fact that it had a sister storm further offshore, will make it an object of fascination for meteorologists for weeks to come, a lot more research will be needed to determine one of the common questions. . in its wake: Can the storm be attributed to climate change?
Unlike the heat dome that hit the West this summer, the factors that contribute to the formation of these mid-latitude storms are more difficult to identify directly with climate change, and that, Castellan said, will be the subject of much scientific analysis during the next years. months.
“Yes, there are fingerprints of climate change in these events,” he said. “(But) the factors that affect this type of climate in the mid-latitudes are going to evolve as the climate changes, and how that is going to evolve specifically is still an academic discussion.”
While bomb cyclones are not common, they are not extremely rare either. The Stanley Park storm in Vancouver in December 2006 and the Solistice Eve storm, which hit British Columbia in December 2018, were examples of the same type of cyclone. Both, however, reached their greatest intensity on land, the latter eliminating the power of some 760,000 inhabitants of British Columbia.