A Pacific "Hurricane" Off the Northwest Coast on Tuesday

An extraordinary storm will develop a few hundred miles off our coast on Tuesday, a storm every bit as strong as a Category 1 hurricane.   But we can't call it a hurricane because of its northern origins and energy source (the energy comes from horizontal temperature differences, not warm water).

A storm with gusts to 80-90 mph, deep low pressure, and huge waves.  Northwest Coast will get a substantial taste of it.

Native Americans were quite familiar with such events and they had some colorful stories of their origins: suggesting they were the result of a giant thunderbird, which lived high in the Olympic Mountains.

The sea-level pressure forecast for Tuesday at 7 PM by the European Center model shows an intense low center with a central pressure of 944 hPa due west of the Washington Coast.  

Trust me, this is an unusually deep low, with most Pacific low centers at this latitude only deepening to 980-990 hPa.  The lines are isobars of constant sea level pressure.

This is a relatively small storm, but one with intense horizontal pressure changes (gradients) and thus very strong winds.   Winds result from differences in pressure.

The sustained wind speed forecast at the same time (below) shows winds stronger that 80 mph just south of the low center.  

Very much like a hurricane with winds going to zero in the center and a ring of strong winds around the low.  You will also note a band of strong winds extending far southeast of the low center:  such winds are associated with an occluded front that projects out of the low.

This storm developed very rapidly (or explosively) the previous 24 hr and thus is considered a "bomb" cyclone (storms that deepen by 24 hPa or more in one day).

The first thing any trained meteorologist does with such an extreme forecast is to compare the prediction to those of other modeling systems.   Most have very similar solutions.  Thus, we have some confidence in the prediction.

Consider the sea level pressure forecast from the UW modeling system (below) for 10 PM Tuesday. The low center is "only" 953 hPa.  Sustained wind speeds are shown by the color shading (knots).

The UW model predicts strong winds (50-70 mph) on the Oregon and Washington coasts. Even stronger along Vancouver Island.

The European Center wave model, shows substantial (significant) wave heights reaching the coast, as the strong winds work on the Pacific Ocean.  20-25 ft waves could reach our coast.

The only reason they aren't higher is because of the relatively small size and rapid development of this storm.

Water levels on the coast are of some concern because the astronomically forced water levels will still be fairly high on Tuesday (see forecasts below for Westport, WA).  So the waves reaching the coast will ride on astronomically high water levels for several hours of Tuesday.

Let me end with the simulated satellite image of the storm on Tuesday night (below).  You can clearly see the low center.  Magnificent.