40 Years Extreme Offshore Waves off the Eastern Continental Shelf of Rio Grande do Norte, Northeast Brazil

Abstract

Unplanned occupations and extreme metocean events increase risk of material and lives losses due to socioenvironmental disasters in coastal zones. Such processes have harmed goods, industries, tourism, traditional populations and sensitive ecosystems along the coast of Rio Grande do Norte State (RN), Northeast Brazil. Long-term monitoring data of metocean drivers are scarce off RN's littoral, which are critical in decision-takings for mitigation and adaptation actions along densely populated coastal areas. This study aims to assess extreme ocean waves off RN's eastern coast. Time series of wind speed, tide and wave parameters have been obtained from satellite altimetry and ERA5 reanalysis, between 1979 and 2021, in a virtual station at 6.0ºS/34.7ºW. Generalized Pareto Distribution (GPD) was fitted to wave significant high (Hs). Registers of coastal disasters were collected from online media. Waves have reached Hs maximum of 3.30 m, average of 0.76 m, coming from east-southeast and southeast. Winter and spring seasons have presented higher waves, related to action of trade winds. Wind speed occurred mainly between 6 and 8 m/s. GPD estimated Hs increasing up to 2.4 times above its average, each 2 years, overtaking 2.7 times its average per decade. Previous increasing of wind speed is more important than its scalar value, to form an extreme wave. Hs at the virtual station had its upper peak either at the same day or one-two days before of coastal damage, which means that ocean storms offshore propagate coastward quickly.