The latest update on El Nino from NOAA remained mostly unchanged and officially on "Watch" status. There's a 60-65 percent chance of a weak El Nino into the fall and winter, according to the consensus of computer models.
While this sounds like a very tepid forecast, there is a little more information. While the water in the El Nino 3.4 zone, the greatest predictor of El Nino, was much warmer than normal in March, some cooler water from the south and upwelling created some pockets of concern for El Nino development. Upwelling is the surfacing of cooler water from beneath.
The 3.4 area, which is the middle of Pacific near the equator, saw signs of warming and below surface measurements indicating a large pocket of warmer water moving to the east. This is called a Kelvin wave, and the most important thing to know is that the movement of a Kelvin wave terminates off the coast of South America and can help back-fill the warmer water to the west. This is what needs to happen to get El NIno back on track in the next few months and there are signs this is happening.
A weak El Nino doesn't help much in determining a larger pattern shift in fall and winter with an increase in rain for Southern California, but it's also not set in stone either.
This is a critical time for the development of El Nino, and if the Kelvin wave indication is accurate, we see more warming at the equator and a stronger signature of El Nino. The trend, in my opinion, is moving in that direction.