Metocean study for the planning of the FSRU terminal: a case study at the Estonian coast of the Gulf of Finland

Metocean extreme-value assessment is a necessary input for the planning of coastal and offshore energy infrastructure, particularly in semi-enclosed basins where wind, waves, sea level, and currents vary strongly over short spatial scales. This study provides a site-specific metocean characterization for the planned Floating Storage and Regasification Unit terminal at Pakrineeme/Paldiski on the southern coast of the Gulf of Finland and places the local results in a Baltic Sea-wide context. Long-term observational, satellite, reanalysis, and numerical model datasets were combined, including Copernicus Marine Service products, ERA5 winds, local sea-level and wind observations, satellite wind and sea-level products, and high-resolution NEMO and SWAN simulations. Extreme values of wind speed, sea level, significant wave height, wave period, and surface current speed were estimated using established extreme-value methods, including block maxima and peaks-over-threshold approaches with Generalized Extreme Value and Generalized Pareto distributions. For the Pakrineeme/Paldiski site, the estimated 50-year marginal return levels are approximately 23 m s ⁻¹ for 10 m wind speed, +1.5 and −0.7 m for sea-level maxima and minima, 4.1 m for significant wave height, and 0.37 m s ⁻¹ for surface current speed. These values provide metocean design-basis information for subsequent engineering assessment, but they do not represent direct estimates of vessel motions, mooring loads, fender loads, structural response, or operational downtime. The Baltic-wide analysis shows strong spatial contrasts in 50-year return levels: the largest wave extremes occur in exposed parts of the Baltic Proper, while the largest positive sea-level anomalies occur in constrained sub-basins such as the Gulf of Finland and the Gulf of Riga. The associated uncertainty fields indicate that regional-scale return levels should be interpreted as screening information rather than locally validated design values. The study demonstrates how harmonized multi-source metocean datasets can support site-specific hazard characterization and regional comparison of infrastructure-relevant extremes in the Baltic Sea.