If you look closely at ENSO (El Niño Southern Oscillation) regions, you can nicely see the developing cold “waveforms”, as the pressure patterns are creating strong easterly surface trade winds. These drive the wind-driven ocean surface cooling, and peak cold anomalies are now focused more towards the eastern regions.
Since early October of 2021, there has been a temperature anomaly in the ENSO 3.4 region that reveals a stronger cooling due to stronger trade winds. Peak anomalies were reached in late October, with another drop-off in December and now in January. The cooling is expected to slowly reduce now, starting the shift into an upward, or warming, trend in the coming months.
The reason for the warming can actually be seen already, as it is lurking below the ocean surface in the equatorial Pacific. Experts who have studied the latest high-resolution depth analysis under the ENSO regions, say there are definitely colder than normal temperatures below the surface in the east.
But these same weather experts say that a strong warm pool is coming in from the west at around 100-250m depth. This is known as an oceanic Kelvin Wave, and will slowly push out the cold anomalies, as we head towards late winter. One way to look at the whole ENSO region temperature strength is by looking at the ocean heat content. This takes the water at depth into consideration as well, not just the surface temperatures.
When studying ocean heat content, you can observe that the cold anomalies which returned last Summer also peaked in mid-October. But lately, the subsurface cold anomalies have weakened, indicating that the La Nina is likely at (or past) its peak, with the warm Kelvin Wave now spreading below the surface.
What does this all mean? The long-range forecast below from ECMWF shows the La Nina reaches peak cooling in January, makes a quick return to a neutral phase in Spring, with a transition into warm conditions by Summer. So, the most recent ECMWF extended seasonal forecast actually shows the developing warm phase (El Nino), starting in late Summer 2022.
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