El Niño Status and Forecast

In the last 30 days, the average temperature in the upper 300 meters (about 1,000 feet) of the eastern Pacific Ocean cooled. The most recent average weekly sea surface temperature (SSTs) across parts of the tropical Pacific Ocean was about 1 degree Celsius below average, indicative of a weak to moderate La Niña event. Also, in this region the near-surface easterly winds strengthened over the central and west-central Pacific, and the Southern Oscillation Index (SOI), which measures the atmospheric circulation in the tropical Pacific Ocean, increased (Figure 13a). These conditions suggest the ocean and atmosphere are working in concert to maintain the La Niña event. This evolution is consistent with past events, in which the atmospheric components of La Niña become strongest and most well defined during the winter.

There is a strong likelihood that the weak to moderate strength of this event will continue for a month or more before it begins to weaken in late February and March, according to the International Research Institute for Climate and Society (IRI). Based on both statistical and dynamical forecast models, there is greater than a 95 percent chance that the La Niña will continue during the January–March period (Figure 13b). In the March–May period, chances become about equal for either a neutral event or a La Niña; by April–June it is likely that neutral conditions will return. Continued La Niña conditions likely will cause dry conditions in Arizona and New Mexico, according to the NOAA-Climate Prediction Center.