One of the most powerful Pacific storms that I've seen in my meteorological career developed off Russia’s Kamchatka Peninsula last Monday. The storm was too far away to produce any unsettled weather along the Central Coast, but nevertheless, we will see the effects of it along our coastline in the form of ocean waves. In fact, the effects of the storm were significant enough that the organizers of the Mavericks International big-wave surf competition in Half Moon Bay decided to hold their event this weekend.
This epic storm developed as the polar jet stream brought glacial air from Siberia west-southward toward the western Pacific, while relatively warm air at the Earth’s surface from the south moved northward, producing a cyclonic wind shear. Like two hands going in opposite directions as they roll a pencil between them, these intersecting air masses liberated unfathomable amounts of latent heat as water vapor condensed into clouds and precipitation. This heat caused surface air to expand and quickly rise into the sky, which decreased air pressure.
When pressure drops fast enough, meteorologists refer to this explosive development as a bomb. On Monday, this storm became a bomb and produced hurricane-force winds. In less than 12 hours, this storm’s surface pressure went from 952 millibars to 932 millibars. These barometer readings rival that of hurricanes.
Monday’s storm produced winds of over 70 knots for more than 36 hours that blew over a wind fetch (distance of water over which the wind blows) that exceeded 500 nautical miles. The greater the wind speed, the higher the waves. The friction between the wind and the ocean’s surface generated 56-foot seas.
As these 50-plus-foot seas develop, they could only reach a 7-to-1 ratio of wavelength to wave height. In other words, a wave with a 7-foot length can rise only 1 foot before it breaks. When these waves crashed, longer wavelengths developed, allowing the seas to increase in height over time. When these gigantic seas moved out from under these winds they became frightfully long period swells.
These longer-period waves, also called forecast forerunners, had intervals of more than 28 seconds. These wave periods were so long, the accelerometers in the NOAA marine buoys that are stationed throughout the Pacific Ocean had a difficult time registering them.
These extraordinarily long interval waves traveled across the vast expanses of the Pacific at more than 30-knots and started to arrive along our coastline late Friday. This northwesterly swell will peak this morning at 7- to 9- feet (with a 19- to 21-second period), decreasing on Monday and Tuesday.
Even through the significant wave height is not particularly high, the extremely long period of this swell will create strong rip currents and large individual sets of waves between intervals of relatively calm oceanographic conditions. Unfortunately, these relatively calm conditions can lull beachgoers in a false sense of security. If you're venturing to the coast, please remember to never turn your back to the ocean and watch these waves from a safe distance.
John Lindsey’s weekly forecast will appear Monday.
PG&E will offer training courses this year for recently discharged veterans that will provide a career path into the energy industry through the utility’s PowerPathway program. For more information, visit www.pge.com.
If you have any questions or comments about weather or this column, I would love to hear from you. You can also subscribe to my daily weather forecast by emailing me at PGEweather@pge.com.