Probabilistic Wave Forecast for Week 2 and beyond Based on NOAA’s Global Ensemble Forecast System

Abstract In this paper, we propose a new capability for an oceanic hazards outlook containing delineations of where winds and waves are expected to have the potential of posing a hazard to either life or property at sea. This new product is based on NOAA’s Global Ensemble Forecast System, focused on developing a probabilistic forecast of 10-m wind speed (U10) and significant wave height (Hs) for week 2. The methodology involves defining temporal and spatial windows to postprocess the ensemble members and analyzing the tail of the probability density function generated by the pooled dataset. Specific thresholds for U10 and Hs as well as probability levels are defined in the algorithm to generate probability maps. The performance is assessed through statistical validation using NDBC buoy data and reanalysis, followed by case studies. Results indicate that the probabilistic forecast is skillful in predicting waves up to 9 m and winds up to 48 kt (1 kt ≈ 0.51 m s −1 ), particularly for extratropical systems. In addition, with weaker signals and lower probabilities forecasted, extreme extratropical events associated with hurricane-force winds could be in many cases successfully detected in the week 2 forecast. Therefore, the probability maps provide valuable guidance for practical applications, helping in decision-making for maritime operations.