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Published November 21, 2012

El Niño Status and Forecast

Data Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)

The evolution of tropical Pacific Ocean conditions during the last month have not been good news for El Niño enthusiasts. The NOAA-Climate Prediction Center (CPC) canceled its El Niño Watch in mid-November and expects that ENSO-neutral conditions will persist through the winter season. Typically, forecasters have very high confidence in the fate of ENSO by November.

Although sea surface temperatures (SSTs) along the equator in the middle and eastern Pacific Ocean maintained above-average conditions over the past 30 days, the atmosphere continued to ignore the ocean. The Southern Oscillation Index (SOI) remained in ENSO-neutral conditions and even increased slightly in the last month, moving opposite the direction it would take if El Niño were gaining steam (Figure 12a). The lack of coordination between the atmosphere and the ocean means there is limited potential for El Niño to develop over the next several months. Slightly above-average SSTs may linger in the Pacific Ocean over the winter season but are expected to have little to no impact on the winter circulation pattern over the western U.S.

Official forecasts issued in early November jointly by the CPC and the International Research Institute for Climate and Society (IRI) depict a greater chance of neutral conditions persisting rather than the development of an El Niño event over the next several months (Figure 12b). While there is a 76 percent chance for neutral conditions during the November–January period, El Niño has only a 24 percent chance of forming; it’s nearly certain that a La Niña will not emerge. The chance of neutral conditions persisting rises over the winter and crests at 79 percent. As a result of the neutral event, the equatorial Pacific Ocean will have limited impact on the winter circulation pattern, allowing other forces to come into play. Dynamical global circulation models are picking up on a weak dry pattern for the winter season across the Southwest. However, confidence in these forecasts remains low due to the lack of a strong ENSO signal.

Notes:

The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through October 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.

 

El Niño Status and Forecast El Niño Status and Forecast

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