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Published October 24, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
A La Niña Advisory issued by the NOAA-Climate Prediction Center (CPC) continues this month as weak La Niña conditions expand and gain strength across the eastern equatorial Pacific Ocean. Sea surface temperatures (SSTs) are about 0.8 degrees Celsius below average in the east-central Pacific, or about 1.4 degrees F, a temperature that marks a weak La Niña event. Water temperatures just below the surface, however, continue a cooling trend and are more widespread this month. The expectation is that this pool of colder-than-average water will surface during the next couple of months and maintain at least weak La Niña conditions. The Southern Oscillation Index (SOI) value is +1, indicating the atmosphere is fully engaged with the current La Niña SST pattern (Figure 11a). As a result, stronger-than-average easterly winds are occuring along the equator along with suppressed convection in the eastern Pacific.
Official forecasts issued by the International Research Institute for Climate and Society (IRI) indicate La Niña conditions have more than a 75 percent chance of persisting through the October–December period. La Niña is expected to weaken by the end of the winter season. Chances for a return of neutral conditions increase to 50 percent by the March–May period (Figure 11b). It’s expected that a return of La Niña will bring dry conditions and seasonal precipitation forecasts issued by NOAA-CPC reflect this, calling for most of Arizona and New Mexico to experience below-average precipitation through April.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through August 2011. 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.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer