A 3-D PE GCM is used for diagnostic study of seasonal variability of the Black Sea. A diagnostic study is made, using the hydrodynamic adjustment method, and based on climatological monthly data sets of temperature and salinity. The monthly climatological circulation shows strong: variability. The intensity of the Rim Current is seasonal, with a maximum in winter - early spring. The circulation pattern, the Rim Current, and the Cold Intermediate Layer (CIL) are quite realistic and comparable with measurements. Strong influence on current is caused by winter mixing, producing different water masses in the shelf and deep sea regions. There are indications of positive feedback between Rim Current Intensification and upwelling/downwelling rates.