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Published May 22, 2013
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
Sea surface temperatures (SSTs) and wind patterns remained virtually unchanged from last month, indicating that ENSO-neutral conditions persisted across the equatorial Pacific. The Southern Oscillation Index (SOI), a measure of the atmospheric response to changing SST patterns, also remained near average over the past month, a further indication that neutral conditions remained firmly in place (Figure 15a).
Official SST outlooks issued by the NOAA-Climate Prediction Center (CPC) and International Research Institute for Climate and Society (IRI) continue to indicate that neutral conditions are likely to persist through the summer season. There is a 60 percent chance of neutral conditions extending through the July–September period, compared to a 27 percent chance that La Niña conditions will return. There is only a 13 percent chance that an El Niño event will develop (Figure 15b). The chance for a return of La Niña has risen slightly from last month’s forecast, but neutral conditions are still the most likely outcome over the summer season. The chance of a neutral-event holding steady at longer time scales through next winter has jumped up considerably since one month ago. Because ENSO events often materialize in late fall, confidence in the evolution of SSTs, and consequently ENSO, will increase in coming months. Without the presence of a La Niña or El Niño, it will be difficult to project with any accuracy the onset and strength of the monsoon.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through April 2013. 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 Dubious, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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