Abstract. Detailed simulation of wind generation as driven by weather patterns is required to quantify the impact on the electrical grid of the power fluctuations in offshore wind power fleets. This article focuses on studying the power fluctuations of high installation density offshore fleets since they present a growing challenge to the operation and planning of power systems in Europe. The Belgian offshore fleet is studied because it has the highest density of installation in Europe by 2020 and a new extension is expected to start operations by 2028. Different stages of the future installed capacity, turbine technology and turbine storm shutdown technologies are examined and compared. This paper analyzes the distribution of power fluctuations both overall and during high wind speeds. The simulations presented in this article use a new t-student distributed wind speed fluctuations model that captures the missing spectra from the weather reanalysis-simulations. An updated plant storm shutdown model captures the plant behavior of modern high wind speed turbine operation. Detailed wake modeling is carried out using a calibrated engineering wake model in order to capture the Belgium offshore fleet and its tight farm to farm spacing. Long generation time series based on 37 years of historical weather data in 5 min resolution are simulated in order to quantify the extreme fleet-level power fluctuations. The model validation with respect the operational data of the 2018 fleet shows that the methodology presented in this article is able to capture the distribution of wind power and its spatio-temporal characteristics. The results show that the standardized generation ramps are expected to be reduced towards the 4.4 GW of installations due to the larger distances between plants. The most extreme power fluctuations occur during high wind speeds, with large down-ramps occurring in extreme storm events. Extreme down-ramps are mitigated using modern turbine storm shutdown technologies; while extreme up-ramps can be mitigated by the system operator. Extreme ramping events also occur at bellow rated wind speeds, but mitigation of such ramping events remains a challenge for transmission system operators.