Hurricanes get their strength from warm ocean waters. But a process called "upwelling" keeps the ocean temperatures quite cool along the entire U.S. West Coast. The constant easterly trade winds on the Central Pacific pull water from east to west away from our coastline.
Water then gets pulled up from the colder, deeper parts of the ocean to the surface to replace the water that moved west, dropping the water temperatures into the 50s or low 60s. Hurricanes need about 80 degree water to survive.
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Editor's note: After publishing this artcile, an astute reader pointed out that there was indeed one Tropical Storm to hit southern California just south of Los Angeles in 1939.
It's the only documented tropical storm or hurricane to strike the California coast, and it was during a strong El Nino year, which meant ocean temperatures were warmer than normal.
For more info on that storm -- www.usatoday.com.