The storm surge of October 20/21 in 2023 impacted the coasts of the German and Danish Baltic Sea with extraordinary water levels. Based on meteorological reanalyses, the event was reconstructed using a hydrodynamic-numerical model and validated by water level measurements. The complex hydrological processes of the storm surge were then analyzed in detail in order to gain insights into the degree of filling of the Baltic Sea, the peak water levels and the duration of the increased water levels. The analysis illustrates the complex challenges in coastal flood protection as a permanent task, especially in the context of climate change and rising sea levels. Hydrodynamic simulations represent a valuable opportunity to reconstruct past flood events in high resolution and thus to integrate them into future planning tasks for coastal protection facilities. The study aims to provide water level information relevant for coastal protection at locations where no water gauges are available. In line with scientific practice, the simulation results are made publicly accessible via the data publisher PANGAEA.