Typhoon Songda originated 5,000 miles from Seattle but could whip up winds on a par with some of the region’s biggest blows.

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Typhoon Songda didn’t make much of a splash earlier this week when it swept harmlessly past the east coast of Japan, hundreds of miles from shore. So it seems incongruous that this waning tropical storm, born 5,000 miles away, now threatens Washington with a Saturday windstorm that could be one of the fiercest in recent history.

But scientists say most major fall storms in the Pacific Northwest seem to share similar tropical roots.

“Every storm isn’t like this, but there’s something special about these guys that start out in the tropics,” said Washington State Climatologist Nick Bond.

Bond, who’s also a meteorologist at the University of Washington, analyzed the Northwest’s seven biggest October storms — dating back to 1934 — and found that all of them were linked to typhoons that originated on the other side of the Pacific.

That includes the granddaddy of them all — the Oct. 12, 1962, Columbus Day windstorm. The infamous storm, which started as Typhoon Freda, whipped up sustained winds of 110 miles per hour in some spots on the coast, killed more than 50 people and felled vast swaths of forest.

But conditions have to be just right for a typhoon to morph into a Northwest storm, as is happening now with Songda, Bond said.

Typhoons and hurricanes are essentially the same type of storm. They’re collectively referred to as tropical cyclones because both originate in warm, tropical waters. Storms born in the Atlantic and in the Eastern Pacific, such as off the coast of Mexico, are called hurricanes. Storms born in the Western Pacific are called typhoons.

Most typhoons either hit land and exhaust themselves or simply peter out as they track across the Pacific. But a few, like Songda, have much farther-reaching effects.

“We don’t really understand what’s so special about the ones that get here,” Bond said.

It’s probably a combination of intensity and location, said Wolf Read, a postdoctoral researcher at the University of British Columbia who specializes in Northwest storms.

After starting as an unimpressive tropical depression on Oct. 8, Songda quickly ballooned into a super typhoon, with winds in excess of 150 mph. It was also well-positioned to be caught up by the jet stream, which is aimed at the Pacific Northwest.

“Typhoon Songda moved into the jet stream while it was still a fully intact typhoon,” Read said. “It had not started degrading.”

The typhoon was loaded with moisture, which got sucked up by the jet stream. The moisture in turn intensifies low-pressure troughs and sets the stage for a big storm.

“It can really provide a kicker that makes these storms even bigger than they could otherwise be,” Read said.

It’s as if Songda is revving up again, though it’s no longer classified as a typhoon, Bond said. It has become what’s called a mid-latitude cyclone, which can be larger than tropical storms.

“This is one of those rare cases where (a typhoon) just happened to get swept up in the right way and get in an environment where it could grow again right off our coast,” Bond said. “When everything comes together like that — look out.”

On Thursday, computer models showed the storm passing directly over Western Washington, said Kirby Cook, science officer for the National Weather Service in Seattle. But even small shifts in the storm track can change which areas will be hit hardest, he cautioned.

Pressure measurements show a very intense low at the heart of the storm, which means high winds. But the pressures aren’t quite as low as those that spawned the Columbus Day storm.

“This doesn’t look as strong as that, right now,” Cook said. “But it may very well end up being the strongest storm we’ve had in the last five to 10 years.”

The current record holder in that time frame is the Dec. 14-15, 2006, Hanukkah Eve storm, which left nearly half of Western Washington residents without power. But like most of the region’s later- season storms, that blast had no obvious connection to any typhoon, Bond pointed out.

“It’s not like every storm is linked to a typhoon,” he said. “We get plenty that aren’t.”