Spatially and temporally coherent northwesterly wind characterizes the climate of coastal California. Coastal waters experience strong, frequent and persistent northwesterly surface wind, especially in spring and summer. Even though land-falling extractropical cyclones commonly occur in winter in Northern California, highest monthly mean wind speeds occur in late spring. Monthly mean wind speeds are greatest in summer for some Central and Southern California coastal waters. In spring and summer, wind measured at buoys 20-220 km (10-120 nm) offshore the California coast from Oregon to the Mexican border can exceed 10 m/s (20 knots) for days to weeks at a time. Wind speeds occasionally exceed 15 m/s (30 knots) from the northwest producing hazardous seas that pose significant risk to commercial, recreational, scientific, and naval operations.

A number of measurement campaigns have explored the structure and magnitude of wind along the California coast (CODE I, CODE II, SCCCAMP, Coastal Waves 1996, etc). Intensive measurement campaigns produced useful data and insights, but few, if any, analyses of such data extend beyond 6 months. An overview of wind observations along the California coast is presented and a climatology of surface wind using 20+ years of National Ocean Data Center buoy data is developed to highlight mean conditions and variability on diurnal, seasonal, and interannual time-scales. A companion paper discusses large-scale patterns of surface and upper-level circulation associated with relatively strong northwesterly wind along the Calfornia coast. The evolution of Spring and summer wind events is highlighted and mechanisms proposed.