In February--April 1991, episodes of 2 to 8 m s-1 westerly winds of 3 to 11 days' duration occurred in the western Pacific warm pool. Resulting modifications of the upper ocean in current and hydrology are quantified using data from an equatorial mooring at 165¿E and from three cruises within 30 days of one another along 165¿E. During westerly wind bursts (WWB) stronger than 4 m s-1, the upper 50 m becomes isothermal to within 0.1 ¿C and sea surface temperature (SST) drops by 0.3--0.4 ¿C between 5¿S and 2.5¿N Conversely, SST stars warming and the upper 50 m restratifies in 4--5 days after the end of WWB. In contrast to previous observations, salinity between 0 and 50 m appears almost unaffected by WWB; it freshens by 0.4 practical salinity unit in March within an area of 1¿--2¿ of latitude around the equator but not necessarily in direct response to WWB. As for zonal circulation, surface equatorial flow accelerates eastward 2--3 days after the beginning of westerlies. Then, after less than 2 weeks, eastward and westward jets both develop from 2¿N to 2¿S in the upper and lower halves of the temperature mixed layer, respectively. Changes in zonal mass transport in this layer were as much as 30 Sv between 2.5¿S and 2.5¿N from one cruise to the next. ¿ American Geophysical Union 1993