The West Coast has a powerful protection from hurricanes. Could climate change weaken it?

 As June 1 – the official start of the Atlantic hurricane season – arrives, a familiar sense of dread rolls over millions from Texas to New England who face the frequent threat of hurricanes and tropical storms that wipe out communities, flood homes and knock out power for days.

Meanwhile, massive coastal cities up and down the West Coast barely blinked when the Eastern Pacific hurricane season started on May 15. Although plagued with wildfires and earthquake risk, the West Coast enjoys seemingly tranquil seas, even though other parts of the Pacific Ocean aren't so lucky. Mexico regularly gets hit with hurricanes and other parts of the Pacific, including Hawaii, face elevated hurricane risk this year.

So why don't residents from San Diego to Seattle also fear hurricanes? And could that change in a world where climate change is disrupting nearly every weather pattern?

Has a hurricane ever hit the West Coast?

It depends on your definition.

Historic records show at least two hurricanes came very close. A hurricane with estimated 75 mph winds affected San Diego on Oct. 2, 1858, passing just west offshore, but not making landfall, according to a 2004 analysis by two hurricane researchers, Michael Chenoweth and Christopher Landsea, published in the Bulletin of the American Meteorological Society.

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The pair found a report in the Daily Alta California from a San Diego correspondent who reported "one of the most terrific and violent hurricanes that has ever been noticed by the inhabitants of our quiet city."

"Roofs of houses, trees, fences, ... filled the air in all directions, doing a large amount of damage, in and about the city, and its immediate vicinity," the account stated. "The streets, alleys, and roads, from a distance as far as yet heard from, were swept as clean as if a thousand brooms had been laboriously employed for months."

A hurricane named "El Cordonazo" approached Los Angeles on Sept. 24, 1939, but lost hurricane strength shortly before moving ashore. It set records for the most rainfall in September, dropping 5.42 inches in LA and 11.6 inches at Mount Wilson, according to records from the National Weather Service office in San Diego.

Arizona also sees rain from tropical systems, said Isaac Smith, a meteorologist with the Phoenix weather service office. Storms and their remnants arrive every few years and can come from the Gulf of California and the Baja Peninsula and even the Gulf of Mexico. In October 2018, Smith said, remnants of two systems dropped 5 inches of rain, making it the wettest October on record in Phoenix.

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Why doesn't California get hurricanes?

Given its history, a hurricane landfall in California is not impossible, but highly unlikely for two reasons: Cold ocean water and upper-level winds.

The south-flowing cool-water California Current along the U.S. West Coast and northern Baja California ensures the water never gets warm enough to fuel a hurricane, according to NASA.

Along the East Coast, the Gulf Stream provides a source of warm (> 80°F) waters to help maintain the hurricane, the National Oceanic and Atmospheric Administration said. Ocean temperatures rarely get above the 70s along the West Coast, too cool to help sustain a hurricane’s strength.