The design of offshore wind turbines is usually based on the semi-probabilistic safety concept. Using probabilistic methods, the aim is to find an advanced structural design of OWTs in order to improve safety and reduce costs. The probabilistic design is exemplified on tubular joints of a jacket substructure. Loads and resistance are considered by their respective probability distributions. Time series of loads are generated by fully-coupled numerical simulation of the offshore wind turbine. Especially the very high stress ranges that rarely occur during a period with constant conditions are decisive for the fatigue design. The peak-over-threshold method is applied to find the probability distribution of the very high stress ranges. The method of maximum-likelihood estimation is used to determine the parameters of the underlying generalized Pareto distribution. Further analysis shows that especially the number of the very high stress ranges, scattering for different time series, has a significant impact on the resulting fatigue damage.