The October cyclone generated 60-foot waves in the Pacific

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The bomb cyclone and atmospheric river that hit northern California in late October produced unusually heavy rains and high winds. But he also beat the California coast with epic ocean waves. During the storm, individual wave heights of up to 60 feet were measured from Washington to California, according to researchers at the Scripps Institution of Oceanography in San Diego.

The storm at the end of October was the second largest wave in the history of the Point Reyes buoy.

(Paul Duginski / Los Angeles Times)

For example, Point Reyes buoy # 29, located in 1,805 feet of water 25 miles west of Point Reyes, recorded a significant wave height of 30.6 feet on October 25. This is the second largest wave event in 23 years for this data logging buoy. It was not until December 2015, an El Niño year, that he recorded larger waves.

Significant wave heights are calculated by averaging the heights of the largest third of the waves over a 30-minute period, according to James Behrens, program director at the Coastal Data Information Program (CDIP). Typically, some individual waves at a given station can go up to twice this average, and the Point Reyes buoy recorded a maximum individual wave height of 50.5 feet.

To the north, Buoy No. 179 off Astoria, Ore., Recorded significant wave heights of 35 feet, with individual waves slightly above 60 feet. This set a record for the station, which went live in 2011.

Later, as the storm eased and the front subsided along the California coast, Buoy No. 71 Harvest, in 1,791 feet of water west of Point Conception, recorded a height of significant wave of nearly 30 feet, with a maximum individual wave height of 50 feet.

The deep low pressure system that generated these historically large and powerful waves was raging off the Washington coast. It was one of a series of storms and atmospheric rivers that hit the west coast in rapid succession from October 19-24. He had undergone an explosive buildup called bomb-cyclogenesis, which meant that his central pressure dropped by at least 24 millibars (a measure of pressure) in 24 hours. Generally speaking, the lower the atmospheric pressure, the more intense the storm.

Mid-latitude or extra-tropical cyclones such as this are low pressure systems that typically occur between 30 degrees and 60 degrees latitude in the northern hemisphere.

It was the second bomber cyclone to develop in this part of the eastern Pacific Ocean in a matter of days. When its central pressure fell to 942.5 millibars on the morning of Sunday, October 24, it set a record for storms in that part of the ocean off the US Pacific Northwest and was equivalent to a Category 4 hurricane. The Saffir-Simpson scale classifies hurricanes according to wind speed and central pressure. At the time, the storm was about 345 miles west of Aberdeen, Washington, and its winds were sweeping across northern California and the Pacific Northwest.

Explanation of how waves are measured.

(Paul Duginski / Los Angeles Times)

The waves produced by the fierce storm were large, but according to a summary from the National Weather Service of Monterey, forecasters were very impressed with the amount of wave energy rising on the beaches. For example, they noted that water flooded most of Carmel Beach and rhythmically splashed against the sea wall. Similar scenes elsewhere suggest the beaches were still in their summer configurations. In other words, not yet sculpted by winter storms, so not as steep and without significant protective sandbanks – not at all prepared for such a powerful blast early in the season.

Satellite images show a classic comma-shaped system, with a deep counterclockwise rotating low off the coast of Washington state and a plume of moisture tracing up to the central Pacific subtropical. This formed the tail of the comma. The remnants of Typhoon Namtheun, which cleared west of the international date line on October 19, contributed to the plume.

This atmospheric river was the strongest to make landfall over San Francisco since January 2017, and the fifth strongest since 2000, according to the Center for Western Weather and Water Extremes. It is the first outstanding atmospheric river to hit the region since February 2015, and the strongest October atmospheric river to make landfall in the Bay Area in 40 years. Torrential rains caused flooding and triggered multiple mudslides and debris in northern California.

The Atmospheric River was like a fire hose driven over central and northern California, reaching its maximum force, a Category 5, near Point Reyes, pounding Marin and Sonoma counties with its most moisture transport. important around noon on Sunday.

As the storm subsided in northern California on Monday, October 25, the sound of the pouring rain was replaced by the whine of jet skis. Towed surfers from Mavericks, the surf spot south of San Francisco in Half Moon Bay, took on the challenge of the waves of the post-bomb cyclone. Surfline reported “victory conditions at sea”, surfers’ lingo for big, ugly, stormy waves. The phrase comes from the 1950s NBC television series of the same name about naval warfare in World War II.

Notably, the CDIP includes last month’s West Coast Cyclone Bomb on a wave record page, as well as East Coast and Nor’easters hurricanes.

CDIP, at the Scripps Institution of Oceanography at UC San Diego, operates more than 30 active buoys along the West Coast with its partners, and is part of a network of approximately 80 stations that also cover the U.S. coasts from Atlantic and Gulf, and locations in the Caribbean, according to Behrens, the program director.

Behrens said his research group was studying buoy wave data, because erosive storms such as recent bomb cyclones “are as powerful as hurricanes on the east coast, and the coasts suffer the consequences.”


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