The linear wind-driven numerical model of Busalacchi and O'Brien (1980, 1981) and the temperature depth observations based on the expendable bathythermograph (XBT) data collected by the volunteer observing ships were used to study the interannual variability of the model upper layer thickness and of the observed dynamic height (0/400 dbar) in the tropical Pacific (10 ¿S--16 ¿N and 140 ¿E--90 ¿W) for the period 1979--1982 leading to the onset of the 1982--1983 El Ni¿o--Southern Oscillation (ENSO) event. Maps of mean and of interannual rms differences for the model and observation show many common features. Maximum interannual variability is found off-equator in the northwest and southwest tropical Pacific and in the equatorial eastern Pacific. However, there are some notable differences, the major one of which is the model's inability to reproduce the countercurrent ridge. A single eigenvector, which is associated with the ENSO's signal, dominates both the model and observation, accounting for nearly 50% of the total interannual variance. This eigenvector represents an east-west oscillation of the tropical Pacific Ocean, and its nearly identical in its spatial structure and time amplitude for the model and observation. As for other basin-wide oscillations with variability of smaller spatial and temporal scales, the model output does not compare well with the XBT data collected by the existing XBT network. Model-observation cross-correlation is high in the western and eastern Pacific but not in the central Pacific, pointing to the difficulties in identifying interannual signals where the signals are small with the existing sparse data coverage. ¿ American Geophysical Union 1987