El Niño Status and Forecast

Below-average sea surface temperatures (SSTs) across the equatorial Pacific Ocean continued during November, with the most recent weekly SST in the Niño 3.4 region measuring about -1.0 degrees Celsius below average. The cooler-than-average temperatures indicate a weak to moderate La Niña event. Stronger-than-average easterly winds along the equator and suppressed convection in the eastern Pacific are also occuring. The three-month average of the Southern Oscillation Index (SOI) value is currently +1.3, indicating that the atmosphere is fully engaged with the current La Niña SST pattern (Figure 12a). Both the atmospheric conditions and the presence of a large pool of cooler-than-average temperatures in the upper 300 meters of the ocean suggest that La Niña conditions will continue, according to the NOAA-Climate Prediction Center (NOAA-CPC).

Forecasts issued by the International Research Institute for Climate and Society (IRI) indicate La Niña conditions have more than a 60 percent chance of persisting through the February–April period (Figure 12b). Chances for a return of neutral conditions increase to almost 60 percent by the March–May period. There is still some uncertainty about the final strength of the event. About half of the forecast models suggest La Niña will reach moderate strength, while the other half indicate it will remain weak. Most of the models project it will peak in intensity between December and January.

It is expected that a La Niña will bring dry conditions to the Southwest, and seasonal precipitation forecasts issued by NOAA-CPC reflect this. Outlooks call for increased chances for below-average precipitation in all of Arizona and New Mexico through the February–April period (see page 14).