El Niño Status and Forecast

A La Niña Advisory issued by the NOAA-Climate Prediction Center (CPC) continues this month as weak La Niña conditions expand and gain strength across the eastern equatorial Pacific Ocean. Sea surface temperatures (SSTs) are about 0.8 degrees Celsius below average in the east-central Pacific, or about 1.4 degrees F, a temperature that marks a weak La Niña event. Water temperatures just below the surface, however, continue a cooling trend and are more widespread this month. The expectation is that this pool of colder-than-average water will surface during the next couple of months and maintain at least weak La Niña conditions. The Southern Oscillation Index (SOI) value is +1, indicating the atmosphere is fully engaged with the current La Niña SST pattern (Figure 11a). As a result, stronger-than-average easterly winds are occuring along the equator along with suppressed convection in the eastern Pacific.

Official forecasts issued by the International Research Institute for Climate and Society (IRI) indicate La Niña conditions have more than a 75 percent chance of persisting through the October–December period. La Niña is expected to weaken by the end of the winter season. Chances for a return of neutral conditions increase to 50 percent by the March–May period (Figure 11b). It’s expected that a return of La Niña will bring dry conditions and seasonal precipitation forecasts issued by NOAA-CPC reflect this, calling for most of Arizona and New Mexico to experience below-average precipitation through April.