Severity of ‘bomb cyclone’ uncertain, but Seattle area should prepare for wind, rain and power outages

The third in a series of “bomb cyclones” running well off the shore along the west coast could bring a huge windstorm to Western Washington.

Or not.

At one end is the possibility that Western Washington will see a fairly typical fall windstorm with gusts of 25 to 35 mph in the Seattle region, 40 to 50 along the coast and 35 to 45 north of Everett, said Kirby Cook, a meteorologist with the National Weather Service in Seattle.

At the other end, the region could see gusts of 65 to 70 mph along the coast, 50 to 65 north of Everett and 45 to 50 in the interior, including in Seattle.

“That’s the least likely scenario with only a one in 10 chance of occurring,” Cook said, “but you can’t rule it out.”

More likely, the storm — which has not even formed yet — will bring winds with maximum gusts of 55 to 65 mph to the coast, 45 to 60 north of Everett and 35 to 45 in the interior, he said. Easterly winds, which blow in through the gaps in the Cascades, could create pockets of higher winds along the I-5 corridor, he said.

“They’re good winds but they’re not uncommon,” he said. “That’s not to say it’s not going to be a significant storm, but definitely we’re not expecting it to be unprecedented.”

The National Weather Service has issued a high-wind watch for Sunday for the coast of Washington; the Strait of Juan de Fuca; and parts of the interior north of Everett including Port Townsend, western Skagit and Whatcom counties, Whidbey Island, and the San Juans.

A bomb cyclone, which is also known as a mid-latitude cyclone, occurs when the hurricane-like cyclone’s central atmospheric pressure drops at least 24 millibars in a 24-hour period, according to Joe Boomgard-Zagrodnik, an agricultural meteorologist for Washington State University.

That means it “seems to explode out of nowhere,” he said.

Though the impact the coming storm will have on Western Washington is uncertain, the central atmospheric pressure “will get down to below 950 millibars and could be one of the strongest low pressure system we’ve ever observed in our region,” said Mike McFarland, another meteorologist with the National Weather Service in Seattle. 

For comparison, the central atmospheric pressure of Hurricane Larry, which brought sustained winds of 80 miles per hour to Newfoundland when it struck the East Coast of Canada in September, was an estimated 955 millibars.

One thing’s almost certain, said McFarland. “Sunday and Monday will be blustery and windy days from San Francisco to Juneau.” People can expect wind and rain and possible power outages.

And if you’ve been thinking about forcing yourself outside to stroll through the rain, consider skipping it and staying inside, he said.

“The main thing is stay away from the trees,” he said. “I know it’s hard because we’ve got so many trees, but do yourself a favor and don’t get hit by branch.”