This is a new mechanism that I just thought of. Perhaps, in a future time, somebody will pick it up. Nobody can do it right now.
For the first time, I've seen a full Pacific cycle. This starts with warm water going west for about 7 years, then blowing out with a big current reversal. Then comes the La Nina, with the cold water.
This is the latest ocean current map. The cold water from the south had zoomed up the smooth concave coast of S. Am. and then it became detached. The current is now being fed from the north.
This warm feed will then hold for 7 years, and then the heat will have built up for a big reversal. That knocks the 'feeder' (low pressure) back south to suck up cold water. That cycle ends quickly.
We have to wait for the bigger cycles to show up, perhaps in a hundred years.