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Published May 23, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
Sea surface temperatures (SSTs) across the equatorial Pacific Ocean continued to warm during the past 30 days, helping to reinforce the ENSO-neutral conditions that began to take hold in mid-April. The NOAA-Climate Prediction Center (CPC) reports that SSTs are currently close to average across much of the east Pacific Ocean and that the lingering La Niña-like atmospheric circulation, including enhanced easterly trade winds along the equator and enhanced convection in the western Pacific Ocean, also have started to wane. The Southern Oscillation Index (SOI) in April fell to -0.3, and the most current three-month moving average of the SOI is now at ENSO-neutral levels for the first time since last summer (Figure 15a). All of these observations indicate ENSO-neutral conditions have returned, at least for the short term.
How long neutral conditions will last is the big question. A substantial pool of water with above-average temperatures has started to accumulate just below the sea surface across much of the equatorial Pacific Ocean, and some of this warmer-than-average water already has surfaced in the far eastern Pacific. This pool has increased the prospect of an El Niño event developing as early as mid-summer, according to the latest forecast model simulations. The official ENSO forecast issued by NOAA-CPC and the International Research Institute for Climate and Society (IRI) indicates nearly a 50 percent chance of an El Niño event developing in the July–September season, matching the forecast chance of neutral conditions continuing (Figure 15b). IRI notes that several models that include information about the current state of the subsurface warm pool favor the development of El Niño conditions as early as July.
Overall, it looks like either ENSO-neutral or weak El Niño conditions will develop during the next six months. If El Niño is able to take hold and develop this fall, it could shift the upcoming fall and winter storm track to favor wetter conditions in the Southwest, providing some desperate drought relief in the region.
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through April 2012. 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, 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.
For a technical discussion of current El Niño conditions, visit :
For more information about El Niño and to access graphics similar to the figures on this page, visit :
Southwest Climate Outlook Staff
- Michael Crimmins, UA Extension Specialist
- Stephanie Doster, Institute of the Environment Editor
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, Managing Editor, CLIMAS Associate Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Dollin, CLIMAS Publications Assistant
- Dave Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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