Seattle, a coastal city, does not experience hurricanes. The atmospheric and oceanic conditions required for hurricane formation simply do not exist at Seattle’s latitude in the Pacific Northwest. This absence of a hurricane threat is due to distinct geographical and meteorological factors that govern storm systems in the Eastern Pacific Ocean. The severe weather that impacts the region is driven by different forces entirely, primarily mid-latitude storm dynamics.
Defining Tropical and Extratropical Storms
A hurricane is the regional name for a tropical cyclone, a low-pressure system fueled by heat and moisture drawn from warm ocean water. To form and maintain strength, these systems require sea surface temperatures of at least 80°F (about 26.5°C) and low vertical wind shear. The warm water provides the massive energy needed for the storm’s powerful circulation and deep atmospheric convection.
The storm systems that commonly affect the Pacific Northwest are known as extratropical cyclones, or mid-latitude storms. Unlike tropical cyclones, these storms are powered by the temperature contrast between cold and warm air masses, rather than warm ocean water. Extratropical cyclones feature weather fronts and are driven by the jet stream, resulting in strong winds and heavy rainfall during the cooler months.
The Cold Pacific Water Barrier
The primary defense for Seattle against tropical cyclones is the consistently cold temperature of the North Pacific Ocean off the Washington coast. Tropical systems require sea surface temperatures (SSTs) above 80°F to sustain themselves, but the waters near Seattle rarely exceed 60°F, even during the summer. This cold water acts as a natural barrier, immediately removing the heat and moisture source a hurricane needs to survive.
A major contributor to this low SST is the California Current, which flows southward from the Gulf of Alaska. This current continuously transports cold water, effectively refrigerating the ocean surface off Washington, Oregon, and California. Any tropical cyclone drifting northward from warmer waters would quickly lose its tropical characteristics and weaken as it crosses this cold current.
Prevailing Wind Patterns and Geography
Beyond the cold water, prevailing wind patterns in the North Pacific Ocean also steer tropical storms away from the Pacific Northwest coastline. Seattle sits in the mid-latitudes, a region dominated by the prevailing westerlies, which flow from west to east. These winds, particularly the powerful mid-latitude jet stream, generally push weather systems parallel to the coast or out into the open ocean.
Any tropical disturbance forming in the Eastern Pacific would have to fight against this dominant westerly flow to make landfall near Seattle. The jet stream often acts as a conveyor belt that carries low-pressure systems rapidly eastward, keeping the strongest parts of the storms offshore. Seattle’s high latitude also places it outside the typical tropical cyclone formation zones, which are closer to the equator.
Seattle’s True Severe Weather Risks
While hurricanes are not a threat, Seattle faces significant severe weather, primarily intense winter windstorms. These powerful events are fueled by the temperature gradients of extratropical cyclones that develop over the North Pacific. These windstorms cause widespread damage, with strong winds leading to downed trees, power outages, and coastal flooding.
The region is also frequently impacted by “atmospheric rivers,” sometimes known as the “Pineapple Express.” These are narrow bands of concentrated moisture that originate near the tropics and deliver tremendous amounts of rain and snow to the Pacific Northwest. These systems pose a major risk for flooding, mudslides, and landslides, especially when they stall over mountainous terrain. Seattle can occasionally feel the effects of a former tropical cyclone, but only after it has weakened and transitioned into a rain-producing extratropical storm.