The zonal distribution of sea surface temperature (SST) in the equatorial Pacific (4°N-4°S, 120°E-80°W) associated with El Niño/Southern Oscillation (ENSO) has been studied by using the seasonal mean file of the Comprehensive Ocean-Atmosphere Data Set (COADS) for the period 1940 to 1983. Although the warmest ocean area in the western central Pacific exhibits very little annual variation, it is very sensitive to the ENSO, displaying large variability during such episodes. The eastward migration of this warmest area (28.5°C isotherm is used here as a criterion related to strong tropical convection and heavy rainfall) is a common feature in the developing stage of almost all ENSO events since 1940, not only for the event of 1982. The extent of its eastward migration varies from event to event and represents a large contribution to the interannual variability of zonal SST distribution in the equatorial Pacific, comparable to the behavior of the equatorial cold tongue in the east The spread of the war... Abstract The zonal distribution of sea surface temperature (SST) in the equatorial Pacific (4°N-4°S, 120°E-80°W) associated with El Niño/Southern Oscillation (ENSO) has been studied by using the seasonal mean file of the Comprehensive Ocean-Atmosphere Data Set (COADS) for the period 1940 to 1983. Although the warmest ocean area in the western central Pacific exhibits very little annual variation, it is very sensitive to the ENSO, displaying large variability during such episodes. The eastward migration of this warmest area (28.5°C isotherm is used here as a criterion related to strong tropical convection and heavy rainfall) is a common feature in the developing stage of almost all ENSO events since 1940, not only for the event of 1982. The extent of its eastward migration varies from event to event and represents a large contribution to the interannual variability of zonal SST distribution in the equatorial Pacific, comparable to the behavior of the equatorial cold tongue in the east The spread of the war...