Western Pacific westerly wind bursts of 1- to 3-week duration are potentially important in triggering and sustaining El Ni¿o--Southern Oscillation events. One such burst of 10-day duration and maximum speeds of greater than 10 m s-1 occurred in May 1986 west of the date line. The response to this westerly wind burst is documented from equatorial current meter moorings, thermistor chain moorings, and sea level and hydrographic data. At 0¿, 165¿E in the western Pacific the thermocline was depressed by 25 m, sea surface temperature dropped by 0.3¿--0.4¿C, and sea levels rose by 10--15 cm a few days after the maximum in westerly wind speed. Likewise, the South Equatorial Current rapidly accelerated eastward and attained speeds in excess of 100 cm s-1. Vertical shear in an approximately 100 m deep surface layer reversed within a few days of the winds, consistent with a simple model of equatorial mixed layer dynamics in which vertical eddy viscosities are inferred to be O(100 cm2 s-1). A sharp Kelvin wavelike pulse in sea level propagated out of directly forced region into the central and eastern Pacific. The pulse took 45 days to travel from Tarawa (1¿N, 173¿E) to La Libertad (2¿S, 81¿W) on the South American coast, at an average phase speed of about 300 cm s-1. This is of the same order of magnitude as, but significantly higher than, the phase speed of a first baroclinic mode Kelvin wave and is probably the result of Doppler shifting by the Equatorial Undercurrent. A rise in sea surface temperature of about 1¿C in 2 days uccurred at 0¿N, 110¿W with the passage of the pulse. However, coincidental meridional advection of a sharp sea surface temperature front, rather than zonal advection of downwelling associated with the pulse, appears to be reasonable for this warming. The relevance of this wind-forced pulse to the subsequent evolution of te 1986--1987 El Ni¿o--Southern Oscillation events is discussed in the light of these observations. ¿ American Geophysical Union 1988