We describe here a nowcast/forecast system for the entire Mediterranean Sea, designed for real-time forecasts and closely resembling operational numerical weather prediction systems. The core of the system is a high-resolution (10 km) three-dimensional primitive equation-based, sigma-coordinate numerical circulation model, assimilating remotely sensed multi-channel sea surface temperature and in situ expendable bathythermograph/conductivity-temperature-depth observational data, using an optimal-interpolational scheme. We present results for 1993 and 1994 from this data-assimilation model, focusing principally on the mesoscale features prevalent in the western and eastern Mediterranean Sea. We show that the model exhibits considerable skill in simulating both the permanent and transient mesoscale features in the Mediterranean. In particular, hitherto less well-known and less well-studied circulation features in the Adriatic and Aegean Seas are carefully examined and presented. Particular care is given to discussing the circulation in the entire Mediterranean, with particular attention to flows through various straits and their variability. ¿ 1997 American Geophysical Union