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Published September 26, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
The march towards a possible El Niño event slowed this past month as sea surface temperatures (SSTs) held steady and even cooled in some areas across the equatorial Pacific Ocean. An El Niño Watch issued several months ago by the NOAA-Climate Prediction Center (CPC) remains in effect this month, meaning that El Niño conditions may still develop in the next several months. Mixed signals across the equatorial Pacific Ocean include a slight cooling of SSTs and weak atmospheric circulation pattern shifts—the Southern Oscillation Index is only slightly negative (Figure 12a)—but widespread warmer-than-average water just below the surface indicates the steady progression towards the El Niño event observed over the past several months has slowed.
Official forecasts issued jointly by the CPC and the International Research Institute for Climate and Society (IRI) still depict a strong chance (82 percent) that El Niño conditions will develop sometime in the September–November period (Figure 12b). This is up slightly from the 78 percent chance forecast last month for the same time period. The chance of El Niño conditions developing is quite high relative to the chance of current neutral conditions persisting (18 percent). Regardless, the event is forecast to be weak at best and is expected to quickly wane in the late winter season. The CPC notes that this may limit the impact that El Niño conditions have on the upcoming winter circulation. A weaker forecast of above-average winter precipitation across the Southwest that is limited to far southern portions of Arizona and New Mexico. Conditions in the Pacific Ocean will continue to change over the next 30 days, and forecasts will continue to be adjusted; confidence in the ultimate fate of the El Niño event will grow in coming months.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through July 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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