In the old days, all of recorded history, we had a classic cycle in the Pacific. The Pacific Equatorial Belt would be fed from the northern waters, and a strong current would go west along the equator. The mechanism for this is quite simple, and involves rising hot water, and the equatorial bulge. Every 7 years or so, the hot water would clog up at the far western end, and barf back, as an El Nino.
The weather people believe that the air drives the ocean currents, and stick with that. It's a horrendous physics error, but it defines them.
In 2016, we had a tremendous event where the Pacific Belt was suddenly fed from the south. This sucked in the Antarctic cold water, and the Pacific Belt became cold. I could tell you about my frozen Tahiti vacation. The old cycle was shattered, and my hypothesis is that this event was the mechanism for a 300 year cold cycle, or Little Ice Age. As usual, all my hypotheses could be easily tested, but never will be.
With the El Nino Watch, since it doesn't exist any more, we just look at why they are being so obtuse.
We look at sea temps and it is obvious that the feed is from the south because of the temperature distortion. All water temps want to be stratified along latitude lines, but ocean currents pull things.
This is the anomaly plot. Flash both pictures in your mind. Something is wrong. However, the weather people choose whatever works for them. There is a mechanism for this, but who cares? Let's have an El Nino party!