El Niño Status and Forecast

The NOAA–Climate Prediction Center (CPC) has issued a La Niña Advisory, which means that a La Niña event has been observed and is expected to continue. In the last month, La Niña conditions continued to strengthen across the equatorial Pacific Ocean. Sea surface temperatures (SSTs) are now 1 degree Fahrenheit below average across the eastern Pacific Ocean, indicating a weak event is underway. The Southern Oscillation Index (SOI) rocketed to a value of 2 in July from a meager 0.1 in June (Figure 14a). This large swing in SOI values is evidence that the atmosphere has noticed the shift towards cooler SSTs in the Pacific Ocean and is responding with large-scale shifts in circulation patterns across the region. Winds from the east also have strengthened along the equator, driving more upwelling of cold water in the eastern tropical Pacific Ocean, which is serving to further strengthen the event.

Forecasts issued by the International Research Institute for Climate and Society (IRI) show a high probability that La Niña conditions will continue to persist and possibly strengthen over the next several months. The chance of the current La Niña event continuing through the upcoming winter season exceeds 90 percent, while there is only a 1 percent chance than an El Niño event will return during this period (Figure 14b). Seasonal precipitation forecasts issued by the CPC reflect the high probability for the La Niña event to continue this winter and show increased chances of drier-than-average conditions across all of Arizona and New Mexico.