The present work describes an operational strategy for the development of a multiscale modeling system, based on a multiple–nesting approach and open–source numerical models. The strategy was applied and validated for the Gulf of Taranto in southern Italy, scaling large–scale oceanographic model results to high–resolution coupled-wave 3-D hydrodynamics simulations for the area of Mar Grande in Taranto. The spatial and temporal high-resolution simulations were performed using the open source.