Today's Major Storm: A Difficult Forecast

Storm day is here for the Northwest.  A strong midlatitude cyclone is now rapidly developing off the Oregon coast, but the forecast is not an easy one:

• This storm is relatively small, unlike the huge storm suggested by the models earlier this week.    Thus, a small error in the track, say 25 miles,  can produce a very different wind forecast for locations on the periphery of the storm (like Seattle).  
• The storm is rapidly intensifying right now, which produces uncertainty on exactly the strength at landfall.

The satellite imagery shows impressive development.  Here is the 8:30AM infrared image.  Nice comma structure and a clearly a single low center with strong sinking behind (denoted by the black notch or slot behind it).

A very wet rain shield leads the low center, as indicated by this morning's radar imagery at the same time.

The storm center nearly went over the NOAA/NWS weather buoy 46002, nearly due west of Coos Bay on the southern Oregon Coast.  The pressure dropped to roughly 983.5 hPa and it is clear that the low passed around 1200 UTC (GMT).  We will use that in a second.  The wind sensor was unfortunately broken on the buoy.

We now have the latest model forecasts.  At the start of the forecast (5 AM, 12 GMT/UTC), it shows a 985 hPa low near 130W off southern Oregon.  From the buoy observations we know that the model is not quite deep enough by a few hPa.

 By 11 AM PDT (18 UTC), the storm has intensified to 972 hPa (13 hPa in 6 hr, which is very rapid), with a huge pressure gradient on the south side.   Very windy along the Oregon coast at that time.

By 2 PM PDT (2100 UTC), the storm deeps to 969 hPa is is right off the Columbia.  Intense winds over the northern Oregon and southern WA coasts.

At 5 PM, the low (967 hPa) is near landfall on the northern WA coast, with very large pressure differences (and powerful winds) along the south/central WA coast.  At this point winds should be accelerating over the Puget Sound interior.

Finally, at 8 PM, the low is over southern Vancouver Island, with a large pressure gradient (and winds) from Seattle northward.  After 9 PM, the low will move out and winds will subside.

I will show you the predicted winds in a second, but the key point is that the large pressure gradients will be over the coast and NW Washington and thus the winds will be more modest south of Seattle over the interior.

And now what you really want to see: the predicted wind gusts.
At 11 AM, some gusts of 50-70 knots along the Oregon coast.

 By 2  PM, the strong winds cover the coastal zone from northern Oregon to central WA.

But now lets zoom in over WA.  At 5 PM (000 UTC), with the low just offshore, crazy winds along the central WA coast (gusts over 70 knots)

8 PM?   Very high winds (60-70 knots) over NW Washington, over the western Strait, and the northern WA coast.  Seattle winds will max out around then to roughly 50 knots (57 mph).   Sustained winds will be much less (perhaps around 30 mph).  Less over Tacoma and Olympia.

 By 11 PM, winds are far less over the entire region.  We are done.

There will be some major wave action with the storm along the coast and localized coastal flooding.   The NOAA/NWS WaveWatch III forecast shows 8-9 meter (about 28 ft) waves on top of an elevated sea surface due to low pressure.

So what the key take aways?  This is going to be bad along the coast and I expect lots of power outages there.  Same for NW Washington, with the San Juans, northern Whidbey, and the Bellingham area to have gusts to 60-70 mph and plenty of power outages.    Much less over the south Sound.

1015 AM Visible Satellite Image of the Storm

Seattle is the difficult forecast...it is at the edge of the stronger winds and a small error in the storm track will make a huge difference.  At this point, gusts to 40-50 mph seem reasonable, roughly 10 mph more than yesterday, with greater winds over the northern side of the side and near the water (where gusts to 50-60 mph could well be observed).  With trees leaves and being early season, power outages over Seattle are expected.

And the most difficult question:  what do we call this storm?  The October Ides Storm?  Sukkot Eve Storm.  Songda Storm.  Someone wanted to call it the Chicken Cacciatore Day Storm (October 15 is Chicken Cacciatore Day).  No.....

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