Data Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
Sea surface temperatures (SST) in the tropical Pacific Ocean are similar to one month ago and are near average across much of the equatorial region. This indicates that ENSO neutral conditions have persisted into July. The NOAA Climate Prediction Center (CPC) noted that although there was some cooling of SSTs to slightly below-average conditions in the eastern Pacific region, the change was small and relatively short lived. Upper- and lower-level winds are also near average, which provides additional evidence that neutral conditions are firmly in place. The Southern Oscillation Index (SOI), a measure of the atmospheric component of ENSO, increased slightly but remains in neutral conditions (Figure 14a).
Official SST outlooks issued jointly by the CPC and International Research Institute for Climate and Society (IRI) continue to indicate that neutral conditions are likely to persist in coming months (Figure 14b). There is a about a 70 percent chance that neutral conditions will persist through the 2014 spring, while there is only about a 20 and 10 percent chance that La Niña and El Niño conditions, respectively, will develop later this fall. However, the CPC notes that statistical and dynamical models are disagreeing substantially over the fate of ENSO this fall, with some forecasting a La Niña while others point towards an El Niño event. This leads to lower forecast confidence this month; confidence will likely increase in coming months as the fate of ENSO usually becomes clearer as the summer progresses.
The first figure shows the standardized three-month running average values of the Southern Oscillation Index (SOI) from January 1980 through June 2013. 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.