El Niño Status and Forecast

It’s official. La Niña is back after a brief, four-month hiatus. A La Niña Advisory recently was issued by the NOAA-Climate Prediction Center (CPC), signaling La Niña conditions have developed and are expected to persist for at least the next six months.

Sea surface temperatures continued to decline across the eastern equatorial Pacific Ocean during the past month, crossing the -0.5 degree Celsius threshold for a La Niña event. Weak atmospheric circulation patterns that began during last winter’s La Niña event have continued all summer and have helped drive the redevelopment of the current La Niña. Southern Oscillation Index (SOI) values remain low but are expected to strengthen in the coming months (Figure 12a).
Official forecasts issued by the International Research Institute for Climate and Society (IRI) put the chance of La Niña conditions persisting through the upcoming winter season at greater than 50 percent (Figure 12b). There is a 48 percent chance of ENSO-neutral conditions returning and only a remote chance of an El Niño event forming through the November–January period.
While forecast models are uncertain about the strength of the current La Niña event, most agree a weak event will persist through the winter at the very least. It is interesting to note that the chance of ENSO-neutral conditions returning by the January–March period is 49 percent, and only 1 percent greater than the chance of La Niña conditions continuing during this period. This is an indication of how weak the La Niña conditions are at this point, and how much uncertainty there is in the ability of this event to carry through until the spring.

Weak La Niña conditions are expected to expand and intensify drought conditions across the southern tier of the U.S., including Arizona and New Mexico. Official seasonal precipitation forecasts issued by the CPC indicate increased chances for below-average precipitation in the Southwest until the spring.