Windstorms

Key Points

• The Puget Sound region experiences strong windstorms, including ones with hurricane force winds known as mid-latitude cyclones. These storms are wider that tropical storms. The largest of these was the 1962 Columbus Day Storm. The moderating effects of the Pacific Ocean prevent hurricanes.

• Puget Sound is sheltered compared to the Washington Coast, but it can still receive sustained winds of 60-70 mph and gusts up to 90mph.573 Local terrain has a strong effect on wind speeds. Winds speed up as they move over hills and ridges.

• Pineapple Express storms also pack strong winds, but these storms are known more for their rain than wind. They occur when the jet stream dips into the tropical regions and up into our area. Wind is just one component of these events that also can include flooding, landslides, and power outages.

• Tornadoes are very rare in the Puget Sound region. Washington ranks 43rd in tornado frequency. Between 1950 and 2005 there were 94 tornados in Washington and most were weak. Those in the Puget Lowland were mostly associated with the Puget Sound Convergence Zone.

• Power outages are the most wide-spread problem caused by windstorms. The 2006 storm overwhelmed Seattle City Light when 49% of its customers lost power. 95% of customers were restored within two days, but full restoration took a week.

• Structural damage is the costliest consequence of windstorms. Much of the damage comes from falling trees.575 Damage can occur at wind speeds as low as 32 mph and destroy wood frame structures at speeds around 100 mph. Seattle's building code requires new structures to withstand 85 mph for three seconds (with modifications to be made for location), but Seattle also has many older buildings. Almost 90,000 homes in Seattle were built before 1939.

• People have died from falling trees and branches. Because many windstorms happen in winter and many residents are dependent on electricity for heat, cold-related health problems are a hazard. Several people were killed in King County while heating their homes with charcoal fires during the power outages following the 2006 storm.

• Large windstorms are regional events. The more heavily forested suburban areas are often hit harder than Seattle is. The result is that resources to aid in recovery can be hard to find.

• Floating bridges are vulnerable to wind and wind-driven waves. The Hood Canal Bridge sunk in 1979 and the I-90 Bridge sunk in 1990.

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