Extreme wave predictions around New Zealand from hindcast data

A recently implemented wave hindcast for the New Zealand region was used in conjunction with wave-buoy data to evaluate extreme significant wave height at multiple sites around New Zealand, for the first time. Hindcast storm wave heights were under-predicted compared with wave-buoy measurements at three inshore sites, and a method for scaling the hindcast data to improve the comparison of predicted extreme wave heights was explored. Different statistical methods for predicting extreme wave heights were also compared. Offshore, extreme wave heights displayed a north-south and an east-west gradient that is in keeping with the mean wave climate, with larger waves in the south and in the west. However, the variation of extreme wave heights between sites was less than the mean wave climate would suggest, because mid-latitude depressions generate comparatively large waves on the generally more sheltered northeast coast. At the most energetic site to the southwest of the South Island, a 1 in 100-year return significant wave height Hs(100) of 19.3 m and maximum wave height Hmax(100) of 45 m were predicted. At the least energetic site to the northeast of the North Island, estimates of Hs(100) = 13.9 m and Hmax(100) = 33 m were obtained.