Environment and Natural Resources Service
FAO Research, Extension and Training Division
The uncertainty of the current situation of the El Niņo-Southern Oscillation (ENSO) derives from the apparent uncoupling of the atmospheric and oceanic components.
While satellites observed a moderate increase of Sea Surface Temperatures (SST), the typical changes in the global atmospheric circulation have not taken place. Analysts indicate that a well developed warm ENSO could be triggered by relatively minor factors, such as strong easterly winds over the Pacific. In addition, the end of April witnessed a relative cooling of the Pacific SSTs off the South American coast.
According to Australian Bureau of Meteorology (BOM) sources, leading models do not concur to predict a full El Niņo, although the situation has changed since the last assessment (see table 1 above).
In February, two out of 13 models (33 %) predicted a warm event for October 2002. In April, the percentage has risen to more than half (55% of 12 models). Based on the figures above, BOM puts the probability of a warm ENSO phase (El Niņo proper) at about 60% towards the end of the year.
The Southern Oscillation Index (SOI) is a synthetic measure of ENSO strength based on atmospheric measurements. It recently underwent marked oscillations around the neutral value (0), with April showing again a tendency to return to average (Figure 1).
Most authoritative sources on El Niņo data, BOM, the US National Oceanic and Atmospheric Administration (NOAA), the International Research Institute for Climate Prediction (IRI) agree that the current period is critical for either El Niņo developing or receding.
1For a general description of the El Niņo phenomenon, please refer to the FAO website: www.fao.org/sd/eidirect/eian0008.htm and to previous El Niņo updates: