The Storm Reveals Itself. The Eastside Wind Threat

The latest satellite image shows the rapid development of the offshore storm.

The visible satellite image around 9 AM was stunning, with low-level clouds swirling around the low center (the orange arrow points to the low center).

Stunning.

Here is the blow-up of the clouds around the low center.  The circulation is obvious.

Strong, rapidly developing storms not only have rising motion that produces clouds, but intense sinking motion that produces a "slot" dry air coming in from the southeast.   

We can view the "dry slot" using satellite images that reveal water vapor content in the upper and middle troposphere.  Such an image is shown below, with blue indicating very dry air.    This is a strong storm... no doubt about it.

The latest National Weather Service surface map (and I do have some issues with the quality of their analyses) shows the storm at 7 AM, with an analyzed lowest surface pressure of  974 hPa.   The storm is rapidly deepening today, so the pressure will fall considerably more.

As I mentioned in my previous blogs, although strong coastal winds are an issue, my biggest concern is for strong winds east of Puget Sound tonight.  

The models are still going for threatening winds....with the clear threat of substantial tree damage and power outages.

The latest European Center forecast predicts winds exceeding 70 mph on the east side of Puget Sound, particularly towards the western Cascade foothills.  These are all easterly and southeasterly winds....not the usual direction of strong local winds.

The NOAA/NWS HRRR model, run at high resolution, is similar but extends strong winds over Whidbey Island and the San Juans.

The UW Model is also threatening with strong winds on the eastside, gusting to 50 kts (around 57 mph) at 10 PM. 

The maximum wind over Seattle based on dozens of predictions is predicted to hit 45-60 mph...from the east (see below). 

Bottom line:  strong winds from the east, gusting to 40-70 mph, will occur east of Puget Sound and will be stronger towards the Cascades.  Expect substantial vegetation damage and many power outages.    Driving down streets with lots of trees might not be a good idea after 6-7 PM if you living in the vulnerable areas noted above.

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Addendum:

Here is the 1 PM satellite image...the circulation has become very, very obvious.

Some satellites can measure low-level winds by measuring wave action...called scatterometers.  Here are the surface winds from a scatterometer around the storm around 12:30 PM PST.    The intense circulation around the low is obvious.

The Deepest Low Pressure Center in Northwest History? Damaging Winds West of the Cascades

 We may break a significant record tomorrow, with the rapid development of the deepest low-pressure center (lowest sea level pressure) on record for the coastal waters of the Pacific Northwest.

For the period of the historical record, the lowest reliable central pressure for any Pacific low-pressure area off the West Coast occurred on October 24, 2021.  I even did several blogs about the event at that time.  As shown in the figure below, at its most intense that storm had a central pressure of 943 hPa.  

The latest model run of the U.S. GFS model predicts that tomorrow's storm will have a low center of 942 hPa

While the European Center has the center at only 943 hPa.  

The fact that multiple forecast models are coming up with the same solution provides great confidence in this forecast.

Ready to be impressed?  Such low-pressure centers are consistent with the central pressures of a category 4 hurricane as shown by the official Saffir-Simpson scale (below).  No need to head to Florida for big storms!

This offshore storm and its associated front will bring major winds to the coast, with coastal winds gusting to 50-65 mph around 6-8 PM tomorrow evening (see predicted winds at 7 PM Tuesday, kt).   Winds will be even stronger over the western portion of the Strait of Juan de Fuca, with gusts above 70 mph.

Coastal flooding will be reduced by the easterly component of the wind, which will act to push water away from the coast.  

But as noteworthy as all this is, the big weather story will be in the western Washington interior, where a ferocious easterly wind will descend the western side of the Cascades, undoubtedly resulting in the loss of power to thousands.  

I am charging my electronics and flashlights right now.

We have a very interesting...and threatening situation developing.  To the west, a record-breaking low pressure center is developing.   But to the east, just the opposite:  cold air is leading to higher pressure than normal.  

Below is the pressure pattern at 10 PM tomorrow night.  The solid lines are isobars, lines of constant sea level pressure. The colors indicated low-level temperatures, with blue being cold and yellow indicate warm.  

The combination of the low offshore and inland cold high results in a crazy intense pressure change over the Cascades.

As shown by the latest high resolution UW forecast of the winds for tomorrow evening around 7 PM, strong easterly winds gusting to 40-60 kt will hit the region from the Cascades to the Sound, and from an unusual direction (from the east).

The NOAA HRRR model does something similar (winds in mph)

These kinds of winds will take out power to thousands:  not only will they be strong, this is early season, and the direction is unusual for the powerful winds. Vegetation is not used to it.  

In Seattle, the southern part of the city is most vulnerable to such strong winds.  Whidbey and the San Juans will be hit hard.

You have been warned. 😉