Tropical cyclones, known as hurricanes in the Eastern Pacific, are powerful weather systems fueled by heat and moisture drawn from the ocean surface, defined by sustained wind speeds reaching at least 74 miles per hour. California’s long coastline often suggests immunity to these storms. However, meteorological history shows that while a full-strength hurricane landfall is exceedingly rare, it is not outside the realm of possibility.
Historical Context of Tropical Storms in California
The only recorded instance of a tropical cyclone impacting the state with hurricane-force winds occurred in 1858. An unnamed Category 1 hurricane passed just offshore of San Diego, causing considerable damage to structures and ships in the harbor. This event demonstrates the historical precedent for such a storm.
The most famous example of a storm making direct landfall was the 1939 Long Beach Tropical Storm. This system is the only tropical cyclone to officially make landfall in California during the 20th century, doing so near San Pedro. By the time it crossed the coast, its sustained winds were around 50 miles per hour, classifying it as a tropical storm, yet it caused widespread flooding and resulted in nearly 100 fatalities, mostly at sea.
Numerous other systems have tracked near or into Southern California, primarily as tropical depressions or post-tropical remnants. Tropical Storm Hilary in 2023 was a notable event, becoming the first tropical storm to prompt a tropical storm watch for Southern California since modern records began in 1949. These events, even when downgraded, confirm that tropical systems can and do reach the state, often bringing significant impacts.
Factors That Limit Hurricane Survival
Hurricanes require sea surface temperatures of at least 79–80°F (26.5°C) extending to a significant depth to maintain their intensity. The dominant influence along the California coast is the cold California Current, which flows south from the Gulf of Alaska. This current, combined with coastal upwelling, brings deep, cold water to the surface. This keeps sea surface temperatures well below the threshold needed to sustain a hurricane’s structure.
As a tropical cyclone moves northward from the warmer waters off Mexico, it rapidly loses its heat source and begins to weaken. The cold water effectively acts as a natural meteorological defense, stripping the storm of the energy required for survival.
A semi-permanent feature known as the Eastern Pacific High is a vast area of high pressure that typically sits offshore. This high-pressure ridge and the prevailing winds usually push any northward-moving storms out to the west, away from the coast, or southward into Baja California.
The atmosphere near the coast is characterized by increased vertical wind shear. Strong wind shear tends to tear apart the vertical structure of a tropical cyclone, separating the storm’s core from its heat source. The combination of cold water, unfavorable steering currents, and high wind shear makes maintaining a hurricane’s tight, organized circulation almost impossible as it approaches the California coastline.
The Typical Impacts of Remnant Systems
When a tropical cyclone remnant does affect California, the primary danger shifts from high winds and storm surge to excessive moisture and rainfall. These systems typically inject deep tropical moisture into the atmosphere, often interacting with the state’s mountainous terrain. This interaction forces the moisture-laden air to rise, cool, and condense, resulting in heavy, widespread precipitation.
The resulting heavy rainfall is the most significant hazard, especially in a state unaccustomed to such tropical downpours. Former Hurricane Kathleen in 1976, for example, dropped a record 14.76 inches of rain on San Gorgonio Mountain, demonstrating the extreme precipitation potential. This intense rain quickly saturates the soil, leading to flash flooding in low-lying areas and dangerous washouts in desert regions.
Mudslides and debris flows are a particular concern, especially in areas recently affected by wildfires. Burn scars leave the ground unable to absorb water, turning intense rainfall into fast-moving rivers of mud and rock. While wind can be a factor, it is generally secondary compared to the flooding and debris hazards posed by the immense volume of water these remnant systems deliver.