Integrated Reanalysis-Based Metocean Characterisation for IEC-Oriented Offshore Wind Screening in the Gulf of Tonkin

Early-stage offshore wind development in the Gulf of Tonkin (Bac Bo Gulf) requires environmental information beyond conventional wind-resource mapping. Waves, currents, directional relationships, and extreme conditions all affect structural loading, operability, and the reliability of preliminary feasibility assessments. Wind, wave, current, and bathymetric data for 1993–2024 were analysed at three representative fixed-bottom screening sites: northern Gulf of Tonkin (NGT), central Gulf of Tonkin (CGT), and southern Gulf of Tonkin (SGT). The analysis characterises long-term conditions, seasonal variability, directional misalignment, wind-conditioned sea states, and marginal extremes with quantified uncertainty. The central site was the most energetic, with a mean wind speed of 7.97 m s−1 at 150 m and a 50-year marginal wind return level of 37.67 m s−1; the southern site had the strongest background current and the most persistent wind–wave misalignment. These differences do not follow a simple north–south gradient, so a single regional environmental description would misrepresent at least one of the three sites. The resulting conditional, directional, event-associated, and marginal-extreme statistics were organised into an IEC-oriented screening framework rather than treated as completed design-load-case inputs. This framework gives developers a basis for comparing site-specific environmental conditions before committing to costly site investigations. However, joint environmental modelling, water levels, tidal and storm currents, site measurements, and load-response analysis remain necessary before detailed design and certification.