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.

_________________________________________

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.