El Niño is an irregular climate phenomenon of the atmosphere and ocean in the Tropical Pacific which returns on the average every three or four years. Characteristic for an El Niño is warmer than normal sea surface temperatures around the equator in the Eastern half of the Pacific basin and a lower than normal pressure difference between Tahiti (18S, 150W) and Darwin (12S, 131E). The reverse situation, with colder than normal sea surface temperatures, is called a La Niña.

The impact of this situation extends to areas far from the Pacific itself. Globally, El Niño La Ni˜a are the main source of interannual variability of climatte, see Fig. 1 and Fig. 2.
See also links listed on the right under "Further information".

Since November 2006, this information is no longer kept up-to-date
Last update: November 9, 2006

Now (November 2006), a small El Niño3 has started.

In October 2006, the value of the Niño3 index was +1.1, against +0.9 in September. The SOI was -1.7 against -0.7 in September. Fig. 3 shows for last October a map of sea surfce temperature (SST) anomalies.
See for more observations of the Tropical Pacific the link on the right under "Ocean observations".

Usually, the Niño3 index is high and the SOI low during an El Niño, while generally during a La Niña the Niño3 index is low and the SOI high. The last very strong El Niño was that of 1997/98. The previous very strong El Niño event occurred 15 years earlier, in 1982/83. Fig. 4 shows the evolution of the Niño index and the SOI over last twenty years.

The Niño3 index is the deviation from the climatological mean in degree centigrade of the average of the sea surface temperature over the area from 5S to 5N and 150W to 90W in the Eastern equatorial Pacific. The SOI (Southern Oscillation Index) is the normalized pressure difference Tahiti (18S, 150W) and Darwin (12S, 131E).

Fig. 3 Sea surface temperature anomalies with respect to the climatological monthly mean, in Kelvin. (Source: NCEP/CPC)

Since November 2006, this information is no longer kept up-to-date
Last update: October 17, 2006
Over the next few months, an El Niño will develop which probably will have a weak to moderate strength.
See also links listed on the right under "El Niño forecasts" and "Seasonal forecasts".

El Niño forecasts are reasonable reliable up to some three or six months ahead. For longer periods, forecasts usually diverge and the quality of the forecasts detoriates. Moreover, there is a kind of predictability barrier around April: making forecasts in December for the following June is much harder than it making forecasts in June for the following December. In Fig. 5 and Fig. 6 examples are given of forecasts for El Niño indices.