Analyzing Self-Organizing Maps of Modeled U.S. Coastal Wind Regimes with a Comparison to Observations

Abstract Wind offshore of the northeastern United States is a vast and plentiful resource. However, wind variability needs accounting for when planning, installing, and operating offshore wind farms. Therefore, increased knowledge of four general areas becomes vital: 1) common coastal wind regimes and their impact on wind energy production, 2) common regime transitions, 3) how near-surface wind shear varies between wind-shear regimes, and 4) whether numerical forecast model skill is regime dependent. A self-organizing map (SOM) clusters hub-height (80 m) wind data from the High-Resolution Rapid Refresh (HRRR) model covering the northeast coast to address areas 1–3. The SOM identifies three general wind pattern types: unidirectional flow, confluent/diffluent flow, and cyclonic/anticyclonic flow. The strongest mean HRRR wind speeds offshore of New York are associated with a low pressure system near Maine (12 m s −1 ) and wintertime–springtime westerlies (11 m s −1 ), while the weakest winds are associated with a nearby high (≤3 m s −1 ) and a diffluence zone (4 m s −1 ). Using a separate SOM trained on 10–80-m wind differences, warm air advection over cooler northern waters typically leads to lower-level stabilization and thus increased shear. Regarding area 4, modeled winds are compared to buoy lidar observations for each SOM regime. As in observations, the HRRR monthly averaged wind speed decreased in the summer. HRRR generally underforecasts wind speed near the buoys, although the monthly averaged bias decreased over 2 years from 1.4 to 0.1–0.2 m s −1 . Greater bias occurred for regimes representing nearby pressure systems, indicating that HRRR skill can be regime dependent. Significance Statement Optimal wind energy utilization requires accurate wind forecasts, which in turn require an understanding of regional wind regimes. Our study used a machine learning method called a self-organizing map to identify the main types of weather regimes that affect offshore wind power for the northeastern U.S. coast: unidirectional flow, confluent/diffluent flow, and nearby pressure systems. In general, a unidirectional wind or a low pressure system north of the domain is a high-wind-speed regime beneficial for offshore wind energy, whereas confluence/diffluence zones or pressure systems within the domain are generally low-wind-speed regimes that are less beneficial for offshore wind energy. Future studies can apply this analysis for regime-based forecasting methods.