A modest low pressure system will move across Vancouver Island, which will bring a good blow to the coast and the western Washington interior. Around Puget Sound we are talking about sustained winds of 20-30 mph, with gust to 30-40 mph. Higher winds over the near the water.
This is not going to be a great windstorm.
The visible satellite imagery this morning shows the low pressure system as a swirl of clouds due west of the WA/OR border, but the structure is not well defined and not indicative of a strong system.
The UW WRF model forecast for 10 PM tonight (below, sea level pressure and sustained wind speed), shows an elongated low (central pressure is an unimpressive 1002 hPa), with the strongest sustained winds over the ocean of 35 kts. Again, nothing to write home about.
The low makes landfall on central Vancouver Island around 4 AM Friday (see below), with wind revving up along the coast and the interior by that time.
Here is a more detailed view of western Washington at 4 AM, sustained winds from Seattle to Tacoma of 25-30 knots.
Switch to gust forecasts. At 5 AM, winds could be getting to around 40 knots around Seattle.
As the low moves northeastward, a surge of westerly flow pushes into the Strait, with gusts of around 50 knots north of Sequim. I wouldn't walk out to the Sequim lighthouse tomorrow morning. It could be the last walk you take.
So what about uncertainty of the forecasts? The latest NWS/NCEP SREF (Short Range Ensemble Forecast System) sustained wind forecast for Sea-Tac Airport suggests a peak of around 15 knots, with only one ensemble member showing nothing, and a few going as high as 25 knots.
The NOAA GFS ensemble (GEFS) forecasts a bit less and there is little uncertainty. Interestingly, the high-resolution member (blue line), which drives the regional forecasts shown above, is an outlier, being considerably stronger than the rest.
So getting back to the bottom line. We are close enough in time to the event and the ensembles are sufficiently close together (low spread) that it appears one can have some confidence in making the following forecast:
Winds will pick up in the western WA interior between 10 PM and 2 AM tonight/tomorrow AM. The strongest winds will probably be between 4 AM and 1 PM Friday. Over central Puget Sound over land, sustained winds of 20-30 mph, with gusts of 30-40 mph are quite probable. Stronger near the water, with gusts to 40-45 mph.
There could be a few scattered power outages, but a late season storm of this magnitude should not be a real problem. Bring your garbage cans in and don't park your car under a decaying tree and you should be fine. And yes...don't hike along the shores of the Strait of Juan de Fuca Friday morning and early afternoon.