WUWT) Sea surface temperature anomalies for the NINO3.4 region of the eastern equatorial Pacific are a commonly used index for the strength, frequency and duration of El Niño and La Niña events. In recent weeks, they have cooled to well below the threshold of El Niño conditions. For the evolution of an El Niño that starts from La Niña conditions, that dip is unusual during the satellite era (since November 1981). See Figure 1. Actually, it’s unusual for any El Niño event over the past 30 years.
This does not mean the El Niño this year has come to an end. A dip of similar magnitude did occur once before in the satellite era, and that was during the evolution of the 1991/1992 El Niño. See Figure 2. The dip in 1991, however, may have been in response to the June 15, 1991 eruption of Mount Pinatubo. There have been no explosive volcanic eruptions comparable to Mount Pinatubo this year. The evolution of the 1991 event is highlighted in purple in Figure below