El Niño Status and Forecast

The La Niña event is expected to continue for the next several months, according to the NOAA-Climate Prediction Center (CPC). Sea surface temperatures (SSTs) in the equatorial eastern Pacific Ocean in the last month were close to -1 degree Celsius below average, indicating a weak to moderate event. Above-average, near-surface easterly winds also persisted over the central and west-central Pacific, causing the Southern Oscillation Index (SOI), which measures the atmospheric circulation in the tropical Pacific Ocean, to remain positive (Figure 13a). Positive SOI values are also indicative of a La Niña event, but the event appears to be waning. Observations of warming SSTs in the far eastern Pacific Ocean and increasing subsurface water temperatures both suggest La Niña may be peaking or may have peaked. In addition, this is the time of year when ENSO events historically begin to lose strength.

The official forecast issued by the CPC and the International Research Institute for Climate and Society (IRI) indicates a 74 percent chance that La Niña will continue during the February–April period (Figure 13b). However, based on both statistical and dynamical forecast models, chances precipitously drop for the continuation of La Niña into the March–May period and beyond. The impacts of the La Niña event, including drier-than-average conditions in parts of the southern U.S., likely will continue through the remainder of the winter and into the spring—despite a weakening event—because changes in atmospheric circulation lag behind changes in SSTs. This is reflected in the recent seasonal forecasts that call for below-average precipitation for both Arizona and New Mexico through the upcoming spring.