3.1      In June 2010, the transition from ENSO-neutral conditions to borderline La Niña conditions was observed. Sea surface temperatures (SSTs) in the central equatorial Pacific Ocean continued to cool. Cooler than average SSTs have been observed east of the date-line (Fig 8). The trade winds in the western Pacific has strengthened above normal values and cloudiness near the date-line continues to be suppressed. These indicators, coupled with a positive Southern Oscillation Index (SOI) since April 2010, are consistent with the developing stages of a La Niña event.

Fig 8. Sea Surface Temperature Anomalies in Tropical Pacific (source US NOAA)

3.2      The latest model forecasts indicate further cooling of the SSTs in the equatorial Pacific (Fig. 9). Based on historical records, it is not uncommon for an El Niño event to be followed by a La Niña event within the same year. The combination of current observations and model outlooks indicate a likelihood of the development of a La Niña event in the remaining months of 2010.

Fig 9. Forecast of the SST Anomalies (source US NOAA)

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