Seven El Niño events that have reached an Oceanic Niño Index (ONI) value of 1.5 during the ONI’s current period of record of 1950-present.  Reaching that ONI value is commonly considered to be the threshold for a strong El Niño event.  However, one of these events, the 1987-88 event, is not usually used for comparisons to other strong El Niño events.  In 1987-88, the peak ONI value of 1.6 was reached during the late summer to early fall.  When the winter of 1987-88 emerged, the time of year where an El Niño has the most effect, the El Niño event was decaying into a moderate to weak El Niño.   For this reason, 1987-88 will not be included in our comparisons of strong El Niño events.  The six strong El Niño events shown in the comparisons below are from the 1957-58, 1965-66, 1972-73, 1982-83, 1991-92 and 1997-98 winter seasons.

Values for ONI peaked in the late fall to early winter during 5 of these El Niño events, with a late winter peak during the 1957-58 and 1991-92 events.  Only the 1997-98 event followed a smooth parabolic curve in ONI values while the other years grew and decayed in a more variable manner. The 1972-73 El Niño peaked in October-December then rapidly declined, while the 1965-66 El Niño peaked at the same time but declined more slowly.