The October bomb cyclone generated 60-foot waves in the Pacific Ocean

The bomb cyclone and the atmospheric river that hit northern California in late October produced unusually heavy rain and strong winds. But it also hit the California coast with some epic ocean waves. During the storm, maximum individual wave heights of as much as 60 feet were measured from Washington to California, according to researchers from the Scripps Institution of Oceanography in San Diego.

Map showing significant wave height at Point Reyes buoy.

The storm in late October was the second largest wave event in the history of the Point Reyes buoy.

(Paul Duginski / Los Angeles Times)

For example, No. The 29 Point Reyes buoy, located in 1,805 feet of water 25 miles west of Point Reyes, a significant wave height of 30.6 feet on October 25th. It is the second largest wave event in the buoy’s 23 years. data recording. Only in December 2015, an El NiƱo year, did it absorb larger waves.

Significant wave height is calculated by taking an average of the height of the largest third of the waves over a 30-minute period, according to James Behrens, a program manager at the Coastal Data Information Program (CDIP). Typically, some individual waves at a given station can lift up to as much as twice the 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 just over 60 feet. This set a record for the station, which came online in 2011.

Later, as the storm weakened and the front fell off the coast of California, No. 71 Harvest buoy, in 1,791 feet of water west of Point Conception, a significant wave height of nearly 30 feet, with a maximum individual wave height of 50 meters. feet.

The deep low-pressure system that generated these historically large and powerful waves billowed off the coast of Washington. It was part of a series of storms and atmospheric rivers that hit the west coast in rapid succession from 19 to 24 October. It had undergone an explosive intensification called bomb cyclogenesis, meaning that its central pressure dropped by at least 24 millibars (a measure of pressure) within 24 hours. In general, the lower the atmospheric pressure, the more intense the storm.

Mid-latitudes or extratropical cyclones like these are low-pressure systems that generally occur between 30 degrees and 60 degrees latitude in the northern hemisphere.

This was the second bombing cyclone to develop in this part of the eastern Pacific in a matter of days. When its central pressure dropped to 942.5 millibars on the morning of Sunday, October 24, it set a record for storms in this part of the ocean off the northwestern Pacific Ocean in the United States, equivalent to a Category 4 hurricane. The Saffir-Simpson scale classifies hurricanes based on wind speed and central pressure. At the time, the storm was about 345 miles west of Aberdeen, Washington, and its winds lifted northern California and the northwest Pacific.

Explains how waves are measured.

(Paul Duginski / Los Angeles Times)

The waves produced by the violent storm were large, but according to a summary from the National Weather Service in Monterey, forecasters were most impressed with the amount of wave energy pushing up on the beaches. For example, they noticed that the water ran over most of the beach at Carmel and sprayed rhythmically against the sea wall. Similar scenes elsewhere suggest that the beaches were still in their summer configurations. In other words, not yet sculpted by winter storms, so not so steep and without significant protective sandpits – completely unprepared for such a powerful explosion in the early season.

Satellite images show a classic comma-shaped system, with the deep low turning counterclockwise off Washington State and a moisture flag stretching back to the subtropical central Pacific Ocean. This formed the tail of the comma. Remains of Typhoon Namtheun, which was scattered west of the international date line on October 19, contributed to the flag.

This atmospheric river was the strongest to land over San Francisco since January 2017, and the fifth strongest since 2000, according to the Center for Western Weather and Water Extremes. This was the first unusual atmospheric river to hit the region since February 2015, and it was the strongest atmospheric river in October to land in the Bay Area in 40 years. Cleansing rains caused floods and triggered several mud and debris landslides in Northern California.

The atmospheric river was like a fire hose trained in central and northern California, reaching its highest strength, a Category 5, near Point Reyes, which hammered Marin and Sonoma counties with its heaviest moisture transport around noon Sunday.

As the storm subsided in Northern California on Monday, October 25, the sound of drum rain was replaced by the buzzsaw-like whine from jet skis. Tow-in surfers at Mavericks, the surf spot south of San Francisco at Half Moon Bay, took up the challenge with the cyclone waves after the bomb. Surfline reported “Victory-at-Sea” conditions, surfing language for big, ugly, stormy waves. The term originates from the 1950s NBC television series of the same name about naval warfare during World War II.

In particular, the CDIP includes last month’s bombing cyclone on the west coast on one page of wave observations, along with hurricanes on the east coast and Nor’easters.

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 about 80 stations that also cover the US Atlantic and Gulf coasts, and locations in the Caribbean, according to Behrens, the host.

Behrens said his research team is studying wave data from buoys because erosive storms such as recent bombing cyclones “are as powerful as hurricanes on the east coast, and coastlines are taking their heads off.”

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