Figure 11. El Niño Status and Forecast
Sources: NOAA-Climate Prediction Center, International Research Institute for Climate Prediction (IRI)

Weak El Niño conditions were present again this month, according to the NOAA–Climate Prediction Center (NOAA–CPC). Sea surface temperatures (SSTs) in the eastern Pacific Ocean cooled slightly to 0.83 degrees Celsius above average from 0.9 degrees C last month, but were still warm enough to be classified as a weak El Niño. Intermittent bursts of westerly winds during the past month have pushed warm water eastward along the equator, helping maintain the above-average SSTs in the eastern Pacific Ocean. The Southern Oscillation Index (SOI) was near zero again this month, indicating that the atmosphere has yet to respond to the current El Niño event (Figure 11a). The International Research Institute for Climate and Society states that the warm water areas are patchy and have not amassed into a structured unit, which may be delaying an atmospheric response. The IRI also states that this pattern is unfavorable for a strengthening of El Niño conditions in the short-term, but a powerful storm system could boost the strength of the El Niño event in the next few months.

Almost all forecast models indicate that at least weak El Niño conditions will persist through next spring. IRI’s probabilistic forecast shows at least an 85 percent chance that El Niño conditions will persist through the January–March season (Figure 11b). The chance that an El Niño event will persist through the March–May period falls to 50 percent, and a return to neutral conditions becomes more probable by March. In the meantime, weak to moderate El Niño conditions likely will bring an increased chance of above-average precipitation during late fall and early winter across southern Arizona and New Mexico.

Southern Oscillation Index graph

ENSO graph

Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through February 2008. The SOI measures the atmospheric response to SST changes across the Pacific Ocean Basin. The SOI is strongly associated with climate effects in the Southwest. Values greater than 0.5 represent La Niña conditions, which are frequently associated with dry winters and sometimes with wet summers. Values less than -0.5 represent El Niño conditions, which are often associated with wet winters.

The second figure shows the International Research Institute for Climate and Society (IRI) probabilistic El Niño-Southern Oscillation (ENSO) forecast for overlapping three month seasons. The forecast expresses the probabilities (chances) of the occurrence of three ocean conditions in the ENSO-sensitive Niño 3.4 region, as follows: El Niño, defined as the warmest 25 percent of Niño 3.4 sea-surface temperatures (SSTs) during the three month period in question; La Niña conditions, the coolest 25 percent of Niño 3.4 SSTs; and neutral conditions where SSTs fall within the remaining 50 percent of observations. The IRI probabilistic ENSO forecast is a subjective assessment of current model forecasts of Niño 3.4 SSTs that are made monthly. The forecast takes into account the indications of the individual forecast models (including expert knowledge of model skill), an average of the models, and other factors.

More Information:
For a technical discussion of current El Niņo conditions, visit:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/

For more information about El Niņo and to access the graphics found on this page, visit:
http://iri.columbia.edu/climate/ENSO/

Back to the Southwest Outlook Main Page