Wavelet transform and cross wavelet transform were applied for analyzing long time series of sea level and alongshore wind stress to identify intraseasonal variability off western South America and the relations with remote and local forcings. Hydrographic data were used to estimate properties of coastal trapped waves with a theoretical model. For El Ni¿o years, we found the existence of intraseasonal oscillations with periods 20--90 days, between 2S and 27S. At the peak of 91--92 and 97--98 EL Ni¿os, we found perturbations in the northern region, probably associated with remotely forced internal Kelvin waves, with periods 6--11 days and phase velocities 160--260 km/day. Between 12S and 15S, during two El Ni¿o events, our calculations show perturbations which appear to be barotropic shelf waves propagating southward with velocities between 110 and 150 km/day and periods between 30 and 50 days.