Offshore wave climate, Perth (Western Australia), 1994–96

Abstract

The offshore wave climate of Perth (Western Australia) was analysed by using 2.5 years of non-directional 20-min wave data collected from March 1994 to August 1996. The mean wave conditions are characterized by a significant wave height (H_s) of 2.0 m and a spectral mean wave period (T_m) of 8.8 s. However, considerable annual variation in the wave conditions is experienced because of a distinct seasonality in the regional wind regime. During summer, daily sea breezes generate moderate seas (ambient H_s 1 to 2 m; T_m <8 s). During winter, frequent storms associated with mid-latitude depressions generate heavy seas and swell (ambient H_s 1.5 to 2.5 m; T_m >8 s). A low-amplitude background swell (H_s ~0.5 m), generated distantly in the Indian and Southern Oceans, is present all year round. Analysis of extreme wave conditions (H_s >4 m) indicates that, on average, 30 storms are experienced annually, and the storms are most frequent and intense during July. Estimates of extreme H_s, based on all available offshore wave data (12 years, 1975–96), for 1- and 100-year return periods, are 6.7 m and 9.8 m, respectively.