Climate Driver Update history
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics

Equatorial sea surface temperatures (SSTs) in the eastern Pacific have cooled in the past fortnight, and are now at neutral levels for the first time since April 2015. Meanwhile, equatorial SSTs in the western Pacific remained warmer than normal in parts. (See: animation of recent SST changes). 

SSTs more than 1 °C warmer than average persist in areas to the north and east of the Australian continent, and around Tasmania.

SSTs in the Indian Ocean broadly remain more than 1 °C above average.

The tropical Pacific Ocean has returned to a neutral El Niño–Southern Oscillation (ENSO) state. Sea surface temperatures across the tropical Pacific have cooled to neutral levels over the past fortnight, supported by much cooler-than-average waters beneath the surface. In the atmosphere, indicators such as the trade winds, cloudiness near the Date Line, and the Southern Oscillation Index have also returned to neutral levels. Outlooks suggest little chance of returning to El Niño levels, in which case mid-May will mark the end of the 2015–16 El Niño.  

International climate models indicate the tropical Pacific Ocean will continue to cool, with six of eight models suggesting La Niña is likely to form during the austral winter (June–August). However, individual model outlooks show a large spread between neutral and La Niña scenarios.

Changes in the tropical Pacific Ocean and atmosphere, combined with current climate model outlooks, suggest the likelihood of La Niña forming later in 2016 is around 50%, meaning the Bureau's ENSO Outlook remains at La Niña WATCH.

Typically during La Niña, winter-spring rainfall is above average over northern, central and eastern Australia.

Climate model outlooks for the Indian Ocean Dipole (IOD) suggest a negative IOD event is likely to develop during the austral winter. However, outlook accuracy for the IOD at this time of year is low. A negative IOD typically brings increased winter-spring rainfall to southern Australia.

May has seen cloudiness near the Date Line return to values closer to average, consistent with a return to a neutral ENSO state.

Equatorial cloudiness near the Date Line typically increases during El Niño (below average OLR) and decreases during La Niña (above average OLR).

Pacific trade winds near the equator are close to normal for the 5 days ending 22 May. Trade winds have largely been close to normal since the start of March. The return to near-normal trade winds is consistent with a return to a neutral El Niño–Southern Oscillation (ENSO) state.

During La Niña events, there is a sustained strengthening of the trade winds across much of the tropical Pacific, while during El Niño events there is a sustained weakening, or even reversal, of the trade winds.

International climate models indicate the tropical Pacific Ocean will continue to cool, with six of the eight models surveyed suggesting La Niña is likely to form during the austral winter (June–August). However, individual model outlooks show a large spread between neutral and La Niña scenarios.

April 2016 SSTs remained more than 1 °C above average over parts of the tropical eastern and central Pacific. However, compared to March, that area had decreased notably, especially north of the equator, and east of 130° W along the equator, where some areas were close to their long term average. The decrease in SSTs in the tropical eastern Pacific is consistent with the decay of El Niño. SSTs northeast of Australia have decreased since March but remained more than 0.5 °C warmer than average.

April NINO values showed that the NINO3 region in the eastern Pacific cooled by 0.7 °C and the NINO3.4 region cooled by 0.5 °C compared to March, continuing the cooling trend since the end of 2015. Values in the Bureau dataset for NINO3, NINO3.4 and NINO4 were +0.8 °C, +1.0 °C and +0.8 °C for April, respectively.

During April, positive anomalies in the central and eastern Indian Ocean expanded, but contracted in the west.

The 30-day Southern Oscillation Index (SOI) to 22 May is -2.6, up more than 11 points since last fortnight (-14.4 on 8 May) and once again in the neutral range. It is likely to rise further in the coming weeks as strong negative values leave the 30-day window.

Sustained positive values of the SOI above +7 typically indicate La Niña while sustained negative values below −7 typically indicate El Niño. Values between about +7 and −7 generally indicate neutral conditions.

The Indian Ocean Dipole (IOD) is neutral. The weekly Dipole Mode Index value to 22 May is -0.33 °C.

Currently all but one of the international models monitored by the Bureau indicate negative IOD conditions are possible by June. However, model skill is generally lower at this time of year, and outlooks should be used with caution. Negative IOD events are more likely to occur during La Niña. Sea surface temperatures (SSTs) remain significantly warmer than average across the tropical Indian Ocean.

The four-month sequence of sub-surface temperatures anomalies shows the clear cooling trend in the top 100 m of the equatorial Pacific since February. Cool anomalies have spanned the entire equatorial Pacific since April. The first week of May saw the removal of almost all the remaining warmer than average water in the top 50 m. Most of the top 50 m of water west of about 150° W is now close to average.

The 5-day sub-surface temperature map ending 22 May shows that water below the equatorial Pacific is below or near average. In some areas, cooler than average waters have now reached the surface.

Sub-surface temperature anomalies more than 3 °C cooler than average continue to expand, particularly in the central equatorial Pacific sub-surface, where anomalies are now more than 4 °C cooler than average at a depth of around 125m.