El Niño Status and Forecast

During the month of October, the sea surface temperature (SST) anomaly in the Niño 3.4 region—the region in the middle of the tropical Pacific Ocean often used to define El Niño–Southern Oscillation events—was 1.61 degrees Celsius below average, indicative of moderate to strong conditions. A La Niña Advisory issued by the NOAA–Climate Prediction Center several months ago therefore remains in effect, which signifies that a La Niña event is being observed and is expected to continue. The Southern Oscillation Index (SOI) remains high but dipped slightly in the last month to 2.6 to 1.8 (Figure 12a). The current La Niña is evolving similarly to past episodes in 1970–1, 1973–4, and 1998–9, according to the International Research Institute for Climate and Society (IRI).

The large extent of cool ocean temperatures below the surface in the central and eastern Pacific Ocean, along with strong trade winds, suggest the current La Niña will persist during the coming months. The strong trade winds will help perpetuate the event because they induce upwelling in the central and eastern tropical Pacific Ocean, bringing the cool water to the surface. However, substantial additional cooling appears unlikely at this point, as November is near the typical time of peak strength, according to IRI. There is also some indication that the current La Niña may have already experienced its peak in October; it is also possible, however, that a second and possibly stronger maximum will come in the next month or two.

Presently, the models and observations indicate an approximately 99 percent chance that La Niña conditions will continue during the November–January period (Figure 12b). The probabilities remain high at 92 percent or greater for the January–March period; they decline to about 62 percent by March–May.