This area is, on average, the second-most active basin in the world. There are an average of 16 tropical storms annually, with 9 becoming hurricanes, and 4 becoming major hurricanes. Tropical cyclones in this region frequently affect mainland Mexico and the Revillagigedo Islands. Less often, a system will affect the Continental United States or Central America. Northbound hurricanes typically reduce to tropical storms or dissipate before reaching the United States: there is only one recorded case of a Pacific system reaching California as a hurricane in almost 200 years of observations—the 1858 San Diego Hurricane.