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Published June 27, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
ENSO-neutral conditions prevail in the tropical Pacific Ocean, but forecast models continue to favor the development of an El Niño later this year. Sea surface temperatures (SSTs), which had been warming in recent months, leveled during the last 30 days but remain near average across most of the eastern equatorial Pacific Ocean. This indicates that ENSO-neutral conditions currently dominate the Pacific Ocean basin, closing the door on the La Niña event of this past winter. This shift back towards average conditions is reflected in the May value of the Southern Oscillation Index (SOI), which returned to near zero (Figure 14a).
Last month, a large pool of warmer-than-average water flowed just below the surface across much of the eastern equatorial Pacific Ocean. Forecasters and forecast models expected this warm water to make its way to the surface sometime within a few months, bringing on weak El Niño conditions as early as this fall. While forecast models continued to favor the development of an El Niño event this month, they now depict the possibility of a slower onset of El Niño. Official forecasts issued jointly by the NOAA-Climate Prediction Center (CPC) and International Research Institute for Climate and Society (IRI) show a near 50–50 split between neutral conditions and El Niño conditions for the July–September period, with chances for the development of El Niño rising thereafter (Figure 14b). If and when El Niño develops, the current expectations are that it will be weak and may not heavily influence weather conditions in fall and winter. This forecast, however, will continue to evolve as the summer progresses.
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through May 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
- Dan Ferguson, CLIMAS Program Director
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, CLIMAS Associate Staff Scientist
- Gigi Owen, CLIMAS Assistant Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Swetish, CLIMAS Publications Assistant
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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