In March 1997, a strong westerly wind event (WWE) occurred in the western equatorial Pacific prior to the 1997--1998 El Ni¿o event. It produced downwelling Kelvin waves that interacted non linearly with the surface temperature, salinity and zonal current fronts located at the eastern edge of the warm-fresh pool (EEWP). This non-linear interaction locally increased zonal currents by a factor of three compared to a theoretical linear response, and advected the EEWP at an unexpected rate (~ 1 m/s) to which the ocean-atmosphere coupled system may have been responding rapidly to trigger El Nino conditions. ¿ 2001 American Geophysical Union