El Niño Status and Forecast

The La Niña event that emerged earlier this summer has continued to gain strength and is currently classified as moderate to strong. A La Niña Advisory issued by the NOAA–Climate Prediction Center several months ago remains in effect, signifying that a La Niña event is being observed and is expected to continue. A large area of below-average sea surface temperatures (SSTs) extends west from the South American coast, past the International Date Line in the middle of the Pacific Ocean; some SSTs are more than 2 degrees Celsius below-average. Southern Oscillation Index (SOI) values also have exceeded a value of 2 for the first time in several years, indicating a strong atmospheric response to the cool water in the eastern Pacific Ocean (Figure 11a). SSTs, the SOI, and other metrics, including stronger-than-average easterly winds along the equatorial Pacific, are evidence that the ocean and atmosphere are working together to support and sustain the current La Niña event at moderate to strong levels over the next several months.

Forecasts issued by the International Research Institute for Climate and Society (IRI) depict a 99 percent chance that La Niña conditions will persist over the next three months (Figure 11b). There is greater than a 90 percent chance that La Niña will persist through next March. La Niña is expected to weaken and possibly exit the scene by later in the spring. In the meantime, La Niña will have a strong impact on the winter season by disrupting the normal winter storm track, pushing it north away from Arizona and New Mexico. Seasonal forecasts reflect this situation and call for increased chances of below-average precipitation from October through March.