Variability of wave parameters and Hmax/Hs relationship under storm conditions offshore the Portuguese continental coast

Abstract

The relevance of long-term wave storm characterization based on in-situ measurements extends from marine ecosystems management to the design of ocean engineering structures. We analyze wave storms recorded over almost three decades (1988–2015) in three points offshore the Portuguese continental coast located between 83 and 97m water depth. We provide Probability Distribution Functions for mean wave direction (θm), directional wave spreading (σθ), significant wave height (Hs), maximum wave height (Hmax), mean wave period (Tz) and, Hmax/Hs relationship based on four storm datasets. In the highly energetic Portuguese west coast (Leix~oes and Sines), Hmax and Hmax/Hs ranged between 5.5 and 17.3m and 1.16 to 2.47, respectively. We conclude that a GEV distribution can represent Hmax and Hmax/Hs variability at the three analyzed locations. Despite the differences in the dataset lengths and the differences in the range and variability of θm, σθ, Tz, Hs, and Hmax, we found that the range and variability of Hmax=Hs are very similar for the four storm datasets. For the analyzed period, σθ ranged between 8 and 52º and 10 to 59º in the west and south coast (Faro Atlantic and Faro Levante storms), respectively, and its variability can be described by a log-logistic distribution.