Current El Niño Situation
An El Niño event is under way in the tropical Pacific and there is a strong consensus that it will continue into the Southern Hemisphere wet season, although it is likely to be much weaker than the 1997/98 event. Anomalously warm waters persist in equatorial areas especially in the NINO3 and NINO4 regions, and the Southern Oscillation Index (SOI) fell to –1.8 for the month of August with a 3-monthly average of –1.1, the lowest since the previous (1997/98) El Niño event. There is considerable enhanced convection along the equatorial region around Kiribati and continued dry conditions over much of Australia.
Present situation and outlook
There has been further development in some El Niño indicators. The Southern Oscillation Index (SOI) dropped to –1.8 (Fig. 1) in August, with a 3-month mean value of –1.1, the lowest since April 1998.
In August, surface westerlies occurred in 68% of synoptic observations at Tarawa (Western Kiribati), the highest frequency since October 1997. Overall, low level easterly trade winds remained weaker than average over the Southwest Pacific. Equatorial sea surface temperatures (SSTs) in the Central Pacific remain more than 1°C above average, and now exceed 1.5°C just east of the date line, and a slight appearance of a horseshoe like pattern of cooler than normal water on both sides of the warmer equatorial waters is now apparent (Fig. 2). However, there has been some cooling in waters along the west coast of South America, which is not a typical characteristic during a developing El Niño event.
The August sub-surface temperature profile for the equatorial Pacific (Fig. 3) shows a significant expansion of positive anomalies (red) in the Eastern Pacific, especially at about 100 metres depth The weakening of trades winds across the Pacific in recent months contributed to this warming in the Eastern Pacific. The trade winds remained weak over much of the Pacific, (apart from the fareast) in the 5-days to 4 September 2002 (Figure 4).
The majority of the global climate models continue to develop the warm El Niño event into the southern hemisphere summer (December – February). A recent World Meteorological Organisation (WMO) statement indicates that the present El Niño will be much weaker than that of 1997/1998.
Although it is likely that this event may be relatively short-lived, conditions in the tropical Pacific are expected to be sufficiently anomalous to create significant consequences in some areas of the region.