Why Pacific hurricanes don’t strike California

Hurricanes form in the Pacific Ocean, but they don’t strike the California coast. Has a Pacific hurricane ever hit California? What weakens the storms before they get there?

The answer to the first question is no — a Pacific hurricane has never hit California. It’s been hit by the remnants of hurricanes and tropical storms, but hurricanes dissipate before they reach California.

Hurricanes and tropical storms get the energy to grow from warm water. They form over waters that are above a threshold temperature of about 80 degrees Fahrenheit — or 26 degrees Celsius. The warm water fuels the storm and lets it build. When the hurricane moves over waters that are below the threshold, the storm weakens.

In the northern hemisphere ocean currents rotate in a clockwise motion between the north pole and the equator. Because of this pattern, the western United States has cold Arctic waters moving down the coast toward the equator. In fact, water temperatures off the California coast are rarely above 60 degrees Fahrenheit — or 15 degrees Celsius. The cool water just doesn’t provide the thermal energy hurricanes need. So hurricanes quickly weaken as they approach California.

Will a hurricane ever hit California? Probably not. California lies about 800 miles from water warm enough to sustain a hurricane. Even a large, powerful hurricane would not be able to cover that distance before weakening. Hurricanes are a severe form of a tropical cyclone. Hurricanes are a low pressure cell that has counterclockwise wind rotation and sustained winds above 74 mph (118 kph). Hurricanes form in tropics between the latitudes of 10 degrees and 30 degrees north during hurricane season, which lasts from June to October. Hurricanes need warm water÷at least 80 degrees Fahrenheit (27 degrees Celsius)÷for their formation and to sustain them.

Hurricanes form both in the Atlantic and Pacific Oceans. Atlantic hurricanes begin as tropical waves that move out of West Africa. As the tropical waves move across the warm Atlantic water, they can develop into tropical depressions, tropical storms, and maybe even hurricanes. Pacific hurricanes form in a narrower band – 12 degrees to 25 degrees north latitude – off the coast of Central America and Mexico. Pacific hurricanes tend to be smaller and less powerful than Atlantic hurricanes.

The East Coast and Gulf Coast of the United States are often hit by hurricanes because of the general trends in hurricane motion. The general trend in hurricane motion is to the west-northwest due to the prevailing winds. Hurricanes that form in the Pacific also follow this trend. This motion takes hurricanes away for the West Coast of the United States.

Another factor that keeps hurricanes from threatening the California Coast is the water temperature. The waters off the California Coast are cool÷rarely above 60 degrees (15 degrees Celsius) because they originate in the Arctic and move south. The cool water will weaken any hurricane that moves toward the California Coast. On the East Coast, the Gulf Stream current brings warm, tropical waters north along the coast. This helps sustain hurricanes if they move up the East Coast.

The cool water temperature has protected the California Coast against hurricanes. Waters warm enough to sustain a hurricane are about 800 miles away. Even a large hurricane would not be able to cross this distance without weakening greatly. There have been the remnants of tropical storms and hurricanes that have moved on to the coast but never a hurricane. One tropical storm came ashore near San Diego and Los Angeles on September 25, 1939. It packed 50 mph (80 kph) winds and heavy rain. The storm left widespread damage and flooding. As a result of the storm, 45 people died.

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