October 17, 2021

A Superstorm of Tropical Origin Will Develop Off the Northwest Coast on Thursday

 I have been watching this storm for a while, and I am now certain enough to tell you about it.

A powerful, unusually deep storm will develop off the Northwest coast on Thursday.

A mid-latitude cyclone that began as a tropical storm (Namtheun), now over the western Pacific.

Below is the 96-hour forecast valid at 5 AM Thursday (PDT) of sea level pressure from the U.S. NOAA/GFS model.   The solid lines are isobars (lines of constant sea level pressure).

Amazing...the storm, located due west of our coast, has a central pressure is 952 hPa, which is very, very low for a mid-latitude cyclone at our latitude.  

This storm is deeper (lower pressure) than the extreme Columbus Day storm of October 12, 1962--the greatest storm to hit the Northwest in 100 years or more.


The highly skillful European Center forecast at the same time (see below) is virtually the same, providing confidence in this prediction.


The simulated satellite image near the time of greatest strength is impressive, with frontal clouds swirling into the center of the low.  At that time, an associated from is making landfall on the BC and Northwest coastline.  Big storm.


As noted earlier, this strong, mid-latitude cyclone (low-pressure center) has its origins in Tropical Storm Namtheun, which is now many thousands of miles away (see visible satellite picture yesterday.)

It is a storm undergoing extratropical transition, changing both its structure and energy sources.   From deriving its energy from the warm waters of the tropical Pacific to the horizontal temperature differences of the midlatitudes.

The meteorological version of a hybrid car.  

Let me show you its path through a series of sea level pressure forecasts by the European Center model.  I put some black arrows in to show you the low center position.

Today at 5 PM...the low center is way over in the western Pacific.

5 AM Tuesday, it has moved northward and to the east

5 PM Wednesday, it has weakened, but is still identifiable, now in the central Pacific.


And by 5 PM Wednesday it has intensified rapidly and is now off our coast.


The storm revs up at an unimaginable pace on Wednesday and Thursday morning, deepening by 48 hPa in the 24h ending 5 AM Thursday.  This makes it a superbomb storm, with the term "bomb" used for storms that deepen by 24 hPa (a unit of pressure) in 24 hr.  This storm DOUBLES that...and does most of the amplification in 12 hr.   Stunning.

Fortunately for us, the storm is predicted to head northward away from the Northwest coast and to weaken as it moves into the Gulf of Alaska.....as suggested by the forecast for Thursday evening (shown below).


What about wind speeds?  The European Center surface wind gust forecasts for Thursday morning predicts around 80 mph near the low and even higher speeds in the coastal waters off northern British Columbia.    

Trust me...this is NOT the time to take an Alaska cruise.

And this storm will produce big waves, with the forecast significant wave heights for 5 PM Thursday reaching 30-35 ft.

The relatively short period of this quickly moving and amplifying storm is helping to keep the waves down to simply huge.

Truly major midlatitude cyclones reaching our shores are often associated with tropical disturbances originating in the western Pacific.  That is true of the great Columbus Day storm.   Tropical cyclones are frequent this time of the year and the jet stream is strong enough to supply needed energy and a fast ride to the east.

And don't forget that our big heatwave in late June could be traced to a tropical cyclone moving northward, causing big downstream waves to develop after it banged into the jet stream.

_____________________________________________

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11 comments:

  1. So, are we in for ANY precip out of this??

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  2. good info...but your referring to "the Northwest Coast" implies that we(PacNW) would be getting hit bigtime...instead, you mean Alaska/upper BC...time for me to grab my blood pressure meds!..lol

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    Replies
    1. Thanks for the clarification. I was confused when I read the post.

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  3. Love that book, just ordered a copy as a former east coaster want to learn about the cool weather we have out here! Thanks again.

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  4. Ok sooooo. What’s going to happen OR, WA and lower BC?

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    Replies
    1. All three. Time to find a sturdy root cellar

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  5. Time to bring in my potted plants off the porch and secure the cardboard pile. The local co-op already has the small gourmet pumpkin pies. It’s that time of the year

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  6. Very happy that monster isn’t coming ashore near here, but it will be interesting to watch develop. A magnificent and terrifying storm and a very good reason to avoid the Gulf of Alaska in Fall. Used to cruise my boat up there, but I always got down to at least Vancouver Island by mid-September. I have total respect for Alaskans who fish those waters. Hopefully this storm will stay far enough out there to only bother folks trying to cross the bars along our coast. Those are already scary enough when storms are lurking offshore.

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  7. Very happy that monster isn’t coming ashore near here, but it will be interesting to watch develop. A magnificent and terrifying storm and a very good reason to avoid the Gulf of Alaska in Fall. Used to cruise my boat up there, but I always got down to at least Vancouver Island by mid-September. I have total respect for Alaskans who fish those waters. Hopefully this storm will stay far enough out there to only bother folks trying to cross the bars along our coast. Those are already scary enough when storms are lurking offshore.

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  8. Folks in the population centers of the PNW aren't really even going to notice this storm, but that hasn't stopped several media outlets from sourcing this post and calling for doomsday already. Way to go!

    Honestly, I'd be more concerned about the storm coming together for 10/25. That one has some serious potential, and the models are all starting to agree on something potentially devastating. I'm not very thrilled about the threat of 85-90+ mph wind gusts in the Willamette Valley on Monday.

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  9. What I don't understand is that lows of that depth require water surface temperatures of 79 degrees F or higher to develop and maintain. I am looking for water surface temperature maps/predictions.

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