Operational Validation of a Deterministic Weather-Window Model for Offshore Operations in the Southern Baltic Sea

Reliable assessment of weather accessibility is essential for offshore operations, particularly in areas such as the southern Baltic Sea, characterized by fetch-limited and highly variable wave conditions. This study combines a methodological review of weather-window approaches with operational validation of deterministic threshold methods. The review identified seven methodological groups: deterministic threshold, probabilistic, ensemble, hindcast-based, stochastic, machine learning, and hybrid approaches. Probabilistic, ensemble, and hybrid approaches offer greater potential for short-term forecasting, whereas deterministic methods were considered suitable for long-term strategic planning. This approach was therefore selected for validation against operational survey records. The framework uses 82 years of hourly ERA5 reanalysis data, significant wave height thresholds (Hs ≤ 0.5, 1.0, 1.5, and 2.0 m), and a 24 h weather-window criterion. Model-derived monthly downtime was compared with observed weather standby hours documented in project records for 40 monthly observations from three survey vessels operating in the Polish Exclusive Economic Zone between 2022 and 2026. The model overestimated monthly downtime, with a mean bias error (MBE) of +73.7 h, MAE = 108.4 h, and RMSE = 135.9 h. The 95% limits of agreement ranged from −152.9 to +300.4 h, with r = 0.764 and R2 = 0.584. The results indicate that the framework is more suitable for long-term strategic assessment of weather accessibility than for precise prediction of downtime during individual survey campaigns.