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Published September 23, 2010
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
A La Niña Advisory remains in effect this month as the current La Niña event continues to gain strength. The NOAA–Climate Prediction Center (CPC) issues La Niña Advisories when conditions are observed and expected to continue.
Sea surface temperatures (SSTs) in the central and eastern Pacific Ocean continue to cool. The most recent weekly measurements indicate that SSTs in the key Niño 3.4 region in the central Pacific Ocean are -1.5 degrees Celsius, indicating a moderate to strong La Niña event; this is somewhat colder than the -1.20 degrees C temperatures observed in August. The Southern Oscillation Index (SOI) remained high again this month, indicating a strong atmospheric response to the below-average SSTs (Figure 12a). Stronger-than-average easterly winds along the equator in the eastern Pacific are helping to elevate cooler-than-average water to the surface, further reinforcing the strong easterly winds wafting across the Pacific. This self-reinforcing cycle between the ocean and atmosphere is expected to help maintain and potentially strengthen the La Niña event through the upcoming fall and winter seasons.
Forecasts issued by the International Research Institute for Climate and Society (IRI) continue to show a high probability that La Niña conditions will persist through at least the winter season (Figure 12b). The chance of the current La Niña event continuing through the January–March period is 90 percent; in contrast, the return of an El Niño event is only 1 percent. The strong indication for a winter La Niña has implications for weather in the Southwest. Seasonal forecasts issued by the CPC indicate increased chances for drier-than-average conditions across all of Arizona and New Mexico through May.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through July 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
- 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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