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Forecasts
Published July 25, 2012

El Niño Status and Forecast

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

An El Niño Watch issued by the NOAA-Climate Prediction Center (CPC) remains in effect this month as sea surface temperatures (SSTs) continue to warm and spread across the eastern Pacific Ocean. SSTs have risen to between 0.5 to 1.5 degrees Fahrenheit across the eastern Pacific as easterly winds along the equator have weakened—the Southern Oscillation Index (SOI) continues to decline (Figure 14a)—both indicative of a shift towards El Niño conditions. An El Niño Watch means that conditions are favorable for an event to form within the next six months. 

 
The CPC notes, however, that dynamical and statistical forecast models differ on whether an El Niño event will form in the next several months or if neutral conditions will persist. Dynamical models—which explicitly model physical prcesses—favor the development of an El Niño by early fall, but statistical models—which rely on ENSO tendencies derived from past events—are less certain that warm conditions will build long enough to sustain an El Niño through the winter season and suggest neutral conditions will persist through next spring. Forecasters, however, favor dynamical models and the expectation is that at least a weak, and possibly a moderate, El Niño will develop by late fall. Official forecasts issued by CPC and the International Research Institute for Climate and Society (IRI) reflect this, indicating that chances for El Niño developing by the September–November period are about 78 percent, with about a 22 percent chance of neutral conditions persisting (Figure 14b). The CPC notes that there is still much uncertainty surrounding the eventual strength and magnitude of the developing event and how much El Niño would impact different geographical regions in the fall and winter. If El Niño does materialize, it will bring increased chances for above-average winter precipitation in the Southwest.
 
 
 
 
 
 
Notes:

 

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