Pronounced low sea levels during the 1997/1998 El Niño are analyzed for the effects of local wind stress curl and baroclinic Rossby waves. The sea levels analyzed were produced by a data-assimilating numerical model (not part of this study), and the wind stress curl is based on the wind stress field used to force the model. Frequency and phase as a function of time are inferred by convolving Morlet wavelets with the sea level and wind stress curl data. At certain times and locations the phase relationships indicate reasonable agreement with a solution to the vorticity equation and identify areas of Rossby wave generation and propagation. In the initial stage of the El Niño the sea level declined as a result of regional variability, but in the mature stage the decline was due to interannual, basin-scale processes.