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Published November 23, 2010
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
During the month of October, the sea surface temperature (SST) anomaly in the Niño 3.4 region—the region in the middle of the tropical Pacific Ocean often used to define El Niño–Southern Oscillation events—was 1.61 degrees Celsius below average, indicative of moderate to strong conditions. A La Niña Advisory issued by the NOAA–Climate Prediction Center several months ago therefore remains in effect, which signifies that a La Niña event is being observed and is expected to continue. The Southern Oscillation Index (SOI) remains high but dipped slightly in the last month to 2.6 to 1.8 (Figure 12a). The current La Niña is evolving similarly to past episodes in 1970–1, 1973–4, and 1998–9, according to the International Research Institute for Climate and Society (IRI).
The large extent of cool ocean temperatures below the surface in the central and eastern Pacific Ocean, along with strong trade winds, suggest the current La Niña will persist during the coming months. The strong trade winds will help perpetuate the event because they induce upwelling in the central and eastern tropical Pacific Ocean, bringing the cool water to the surface. However, substantial additional cooling appears unlikely at this point, as November is near the typical time of peak strength, according to IRI. There is also some indication that the current La Niña may have already experienced its peak in October; it is also possible, however, that a second and possibly stronger maximum will come in the next month or two.
Presently, the models and observations indicate an approximately 99 percent chance that La Niña conditions will continue during the November–January period (Figure 12b). The probabilities remain high at 92 percent or greater for the January–March period; they decline to about 62 percent by March–May.
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through September 2010. 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, the 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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