El Niño/Southern Oscillation (ENSO)

The tropical Pacific is currently in a moderate La Niñastate, with atmospheric indicators having intensified the last month. 

The tropical Pacific is currently in a moderate La Niñastate, with atmospheric indicators having intensified the last month. The SOI rose significantly to +2.3 in December (+1.3 in November), the TRMM ENSO index intensified to –1.7 (–0.6 in November), and tropical easterly wind anomalies strengthened west of the Date Line.

The OLR pattern has become extremely intense near the Date Line, with very positive OLR (suppressed convection) along the equator from 150°E to 180, and strongly enhanced convection in a band from Indonesia (associated with a strengthening MJO) through Solomon Islands and New Caledonia to the north of New Zealand.

Sea surface temperature anomalies have weakened slightly in the east–central equatorial Pacific (NINO3 was –0.6°C in December compared to –0.9°C in November), but the anomalies have become more negative near the Date Line (NINO4 intensifying from –0.4°C to –0.9°C).

A negative sub–surface sea temperature anomaly exceeding –3°C remains prominent near 120°W and 100 m depth. All but two dynamical ENSO models NIWA monitors predict La Niña conditions through to March, with weakened La Niña conditions through austral autumn 2012.

The statistical models suggest La Niña through austral summer. The Australia Bureau of Meteorology summary of global guidance states that La Niña is likely to persist through the north Australian wet season, and it is unlikely that the current event will be as strong as 2010–11. The NCEP ENSO discussion of 8 December 2011 indicates that La Niña may peak during summer and then gradually weaken. The models are roughly split between those that predict La Niña to remain weak (3–month average in the NINO3.4 region less than –0.9°C) and those that predict a stronger episode.