Reposted from The Cliff Mass Weather Blog

January 06, 2021

North Pacific “Hurricanes”

 The north Pacific Ocean will never experience a hurricane:  a tropical storm with a sustained wind speed of 74 mph or more.

They aren’t called hurricanes not because north Pacific storms aren’t as strong or stronger than many hurricanes, but because they are not tropical in character.

Clouds swirl into a very deep low pressure center south of Alaska.

During the past few weeks, a number of extraordinarily intense north Pacific storms have formed, with several them putting most tropical hurricanes to shame.  And a major Pacific storm will develop west of our coast later this week, producing huge waves and swell.

Consider the NOAA Ocean Prediction Center sea level pressure analysis for 10 AM PDT 31 December 2020.  A low center near the southwest portion of the Aleutians had a central pressure of 921 hPa (mb), which is unbelievable.  The DEEPEST LOW PRESSURE ON RECORD IN THE BERING SEA.  It was the strongest storm to ever hit Alaska.

How does the low pressure of this storm compare to hurricanes?  Consider the Saffir-Simpson hurricane categories often described by the media.  The pacific storm near the Aleutians that day had a central pressure at the boundary between a Category 4 and Category 5 hurricane. And the associated winds greatly exceeded the requirements for a hurricane.  ANOTHER low center (cyclone) to its east (west of our shores!) had a central pressure of only 972, similar to a category 2 hurricane.

And consider this:  Hurricane Andrew, which brought catastrophic damage to southeastern Florida in 1992, had a central pressure of 922 hPa (mb)) and was a Category 5 storm,  and Category 5 Hurricane Charley made landfall in Punta Gorda, Florida, in 2004 with a central pressure of 941 hPa. Hurricane Katrina at 920 hPa caused widespread devastation along many highly populated areas of the central Gulf Coast and had the third lowest central pressure ever recorded in that area.
And there is something else:  north Pacific storms are much larger in size that tropical hurricanes.  To demonstrate, here are images of the December 31 North Pacific Storm and Hurricane Laura (Cat. 4), using the same horizontal scales. Two to three times as large.

Hurricanes get their energy predominantly from the heat of evaporated water, which is released as latent heat in the storm as massive amounts of water condenses.  Thus, hurricanes require warm water (above about 80F) to survive.   North Pacific storms secure their energy from differences in temperature between the Arctic and subropics.
Another strong Pacific “hurricane” is predicted to form a thousand miles west of us on Friday/Saturday, with a low center of 960 hPa.  Just slightly weaker than the great Columbus Day Storm of 1962.

The sustained winds at that time (see below) indicated a large area above 55 knots (63 mph) and surely the strongest winds will exceed hurricane strength 

And don’t worry about it hitting Washington State:  it will swing northward into the Gulf of Alaska and eventually weaken.  But the storm will produce HUGE waves, reaching 40-50 ft (significant wave height, see forecast for Saturday) and some of those will reach our shores on Sunday (see forecast graphic), although considerable attenuated (perhaps 30 ft).

via Watts Up With That?

January 7, 2021 at 12:38PM