El Niño Status and Forecast

An El Niño Watch issued by the NOAA-Climate Prediction Center (NOAA-CPC) remains in effect this month, as warmer-than-average sea surface temperatures (SSTs) were present again this month across the eastern Pacific Ocean, slightly increasing in extent and intensity over the past 30 days. However, atmospheric circulation patterns, including winds along the equator and areas of tropical thunderstorm activity, so far have responded weakly to the shift towards warmer SSTs, slowing the progression of the El Niño event. The Southern Oscillation Index (SOI) increased slightly in the last month and still remains reflective of ENSO-neutral conditions (Figure 14a).  NOAA-CPC notes that statistical and dynamical models continue to show an eventual progression towards El Niño conditions in the next month or two. As a result, NOAA-CPC may issue an El Niño Advisory in the next month or two as El Niño conditions strengthen.

Official forecasts issued jointly by NOAA-CPC and the International Research Institute for Climate and Society (IRI) depict a strong chance of El Niño conditions forming in the next several months and likely continuing through the spring season of 2013 (Figure 14b). Most models forecast that the event will be weak to moderate in intensity, with only a couple of dynamical models betting on a strong event forming. Chances are greater than 75 percent that an El Niño will develop in the August–October period and they remain above 70 percent through the December–February period. Seasonal climate forecasts for the upcoming fall and winter seasons pick up on the expectation of an El Niño event and forecast increased chances of above-average precipitation across parts of southern Arizona and New Mexico. However, a wet winter for the Southwest is not a slam dunk. While El Niño events typically favor above-average precipitation, in the past weak to moderate El Niño events have delivered below-average winter precipitation for Arizona and New Mexico. Despite this, seasonal forecasts call for a slightly increased chance of above-average precipitation, especially in the January–March period.