Good quote, I'll try to find something a bit more definitive about El Nino if I can.
The article says
Study co-author Mark Cane of Columbia University, who is a pioneer in El Niño forecasting, says computer models have failed to accurately simulate changes in the tropical Pacific Ocean during the past few decades.
Doubt that climate modelling existed prior to the last few decades, so what is essentially being said is that El Nino conditions have so far proven difficult to forecast. They occur anywhere from two to seven years apart.