El Niño / Southern Oscillation (ENSO)

Tropical Pacific conditions are still in the neutral range, however, ocean surface warming has intensified along the equator east of the Dateline towards the South American coast. The latest weekly Nino3.4 index indicates central-western equatorial Pacific ocean temperatures are above normal (+ 0.6).

The SOI is in its third consecutive month of negative values, and has dropped from –0.3 standard deviations in May to –1.2 in June.

The trade winds have weakened further over the past two weeks, and westerly anomalies exist from the Dateline east to about 130°W.

Sub–surface temperatures and upper ocean heat content across the equatorial Pacific have continued to rise in the past month. The volume of above normal sub–surface water is now continuously spread across the equatorial Pacific, centred on a depth near 150m west of the Dateline to near the surface in the far east.

TRMM ENSO index for the 30 days (ending the 27 May) has eased off to –1.2 (from –1.5 before), and is still in La Niña territory.

The OLR pattern across the equatorial Pacific still shows that enhanced convection is present over Indonesia, while convection is reduced north of the Equator east of the Dateline.

The SPCZ is currently lying close to its climatological position.

A MJO pulse crossed the Pacific during the first half of June. A new MJO event is expected to intensify in the Indian Ocean in the first week of July but this will not affect the Pacific before mid–July.

International climate guidance is in consensus that the tropical Pacific Ocean is likely to warm further over the next three months and conditions are likely to cross the El Niño thresholds in a persistent manner by the end of the forecast period.

Of the models NIWA monitor, no climate models favour a return to La Niña for the July–September period. 

Surface temperature anomalies (°C) for June 2012