List of California Hurricanes - An Improbable Event

An Improbable Event

There are two reasons why tropical cyclones rarely strike California: sea surface temperatures, and the usual upper level steering winds in the eastern Pacific, with sea surface temperature being the most important.

Tropical cyclones usually require very warm water to depth, generally above 26.5 °C (80 °F) extending to a depth of 50 metres (160 ft).

The waters off California are cold even in summer. They rarely rise above 24 °C (75 °F) in near-shore southern California, and usually don't get above 17 °C (63 °F) along most of the rest of the coast and outer coastal waters, although El Niño events may warm the waters somewhat. This is due primarily to the extensive upwelling of colder sub-surface waters caused by the prevailing northwesterly winds acting through the Ekman Effect. The winds drive surface water to the right of the wind flow, that is offshore, which draws water up from below to replace it. The upwelling further cools the already cool California Current which runs north to south along coastal California and even much of coastal Baja California. This is the same mechanism which produces coastal California's characteristic fog.

The second reason is the general path of tropical cyclones in the eastern Pacific. They generally move north-westward or westward due to steering by the prevailing upper level winds, which takes them far out to sea and away from land.

These factors make eastern Pacific landfalls improbable north of about central Baja California. In those instances when upper level steering winds do allow a more northerly path, much cooler sea surface temperatures quickly weaken tropical cyclones that approach California, although torrential rainfall can still occur. For example, the September 24-hour rainfall record for Los Angeles is held by the 1939 Long Beach Tropical Storm, as of January 2007.

Read more about this topic:  List Of California Hurricanes

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