— Paul Pukite (@WHUT) August 17, 2017
Applying the ENSO model to predict El Nino and La Nina events is automatic. There are no adjustable parameters apart from the calibrated tidal forcing amplitudes and phases used in the process of fitting over the training interval. Therefore the cross-validated interval from 1950 to present is untainted during the fitting process and so can be used as a completely independent and unbiased test.
Note that each of the El Nino peaks and La Nina valleys defined as "ENSO years" is predicted.
This is simply ocean tidal analysis applied on a different scale. Solving Laplace's tidal equations is the first step, and determining the lunar forcing constituents at a monthly and fortnightly scale is the key.
I will present the ENSO model at this fall's AGU meeting (should the abstract get accepted)