El Niño / Southern Oscillation (ENSO)

Tropical Pacific conditions are in the neutral range, after the end of the 2011/12 La Niña event. The SOI value for May (and the 3 month mean) was –0.3 standard deviations.

The trade winds have weakened slightly over the western and central tropical Pacific during the past two weeks, while conversely the TRMM ENSO index strengthened to –1.51 for the 30 days to 27 May.

The OLR pattern across the Equatorial Pacific remains patchy (having lost the La Niña signal). Eastern–central tropical Pacific SSTs are now very close to the exact climatological average (the weekly NINO3.4 SST anomaly is 0.0 °C), but SSTs are above normal along the South American coastline for the second month running.

There are volumes of subsurface water more than 2 °C warmer than usual in both the western and far eastern equatorial Pacific, although the warm anomaly focus is somewhat deeper in the western Pacific.

The Madden– Julian Oscillation (MJO) has not contributed significantly to tropical convection for most of May. It is forecast to remain weak for the next two weeks. The SPCZ is currently lying close to its climatological position.

International guidance is in consensus that the tropical Pacific Ocean is likely to warm further over the next six months.

All seven models that the Bureau of Meteorology surveys indicate conditions are likely to approach, or possibly exceed, El Niño thresholds during the second half of the year. This suggests an enhanced risk of El Niño conditions developing during 2012. No climate models favour a return to La Niña. 

Dave Gibb, NIWA
The SMARTi intelligent universal interface (Photo: Dave Gibb, NIWA)