We examine the climatological and anomalous response of an isopycnic coordinate general circulation model, with embedded bulk surface mixed layer model, when forced by observed monthly mean wind stress variability. Our results show that model fields of sea surface temperature (SST) and currents are fairly similar to those arising in other models as well as published observations. The model generates a climatology of SST which is usually within 0.5¿--1.5 ¿C of the Comprehensive Ocean-Atmosphere Data Set observations. Anomalous SST compares best with observations when averaged over rather large spatial regions. The mean horizontal currents tend to resemble the observed, but the amplitudes are smaller than observed (primarily because the model predicts vertical mean currents in the mixed layer rather than the surface currents) and the springtime reversal of the South Equatorial Current is absent in the model. Anomalous zonal currents are similarly reduced in amplitude though the variability is comparable to the available observations. We also describe the model's basin-scale mean mixed-layer structure and the mean vertical field (which is fundamentally different from that of the Geophysical Fluid Dynamics Laboratory model). We discuss various aspects of the 1982--1983 El Ni¿o in particular detail, including the heat budget of the variable-depth tropical Pacific surface mixed layer, and the relationships among anomalies of mixed-layer depth, thermocline depth, and SST. By these analyses, we identify the strengths and weaknesses of the model's capability to simulate observations, particularly with respect to that of other models. Throughout the paper, we attempt to identify the primary areas which require improvement in the model and suggest possible remedies. ¿ American Geophysical Union 1992