The average tropical Pacific sea surface temperature anomaly (SSTA) in the NINO3.4 region (5N-5S, 170W-120W) is often used as an El Nino index.
The figure shows our latest forecast using a neural network model trained with data up to May 1998. The four panels are for 3-, 6-, 9-month and 12-month leadtimes respectively. The black line is the observed SSTA (in degree Celsius), and the blue circles are forecasts.
Forecasts of all 4 leadtimes indicate that the current El Nino condition has peaked and the NINO3.4 index will taper off in the coming months. The 6-, 9- and 12-month forecasts also indicate that a La Nina event (cold condition in the tropical Pacific) will come by the end of 1998.