Offshore wind turbines are prone to fatigue caused by wind, wave, and operational loads, and lifetime extension may be enabled by monitoring stress histories. However, this is challenging because parts of the structure are sub‑sea and sub‑soil parts. Model‑based virtual sensing offers a solution, but current models simplify the rotor, which can lead to errors. This work addresses these errors and concludes that accuracy may be improved by including a flexible-rotor model and environmental variability.