The El Niño events of 1997-1998 and 2015-2016 El Niño (at bottom of the plot) were unusually strong.
El Niño: The warm water (red) penetrating eastward in the Spring of 1987 (at the top of the plot) was the El Niño in 1986-1987.  The warm water penetrating towards the east in the northern hemisphere spring of 1992 is the 1991-1992 El Niño.  The El Niño events of 1997-1998 and 2015-2016 El Niño (at bottom of the plot) were unusually strong.