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

Sea surface temperatures (SSTs) in the central tropical Pacific have cooled over the past fortnight, continuing the cooling trend observed since late 2015. SSTs still remain above El Niño levels, with warmer than average waters extending across the eastern and central Pacific. The pattern of warmer waters has started to break down from its tongue-like appearance (see animation of recent SST changes).

Warmer than average SSTs continue to surround most of the Australian continent, with large parts of the southern and northern coastline more than 1 °C above average. To the immediate west of southern WA, SSTs are closer to average, with a small area of cooler waters appearing during the past fortnight.

Warm anomalies continue to cover much of the Indian Ocean, with large parts of the basin more than 1 °C above average.

While the 2015–16 El Niño remains at weak to moderate levels, recent changes in the tropical Pacific Ocean and atmosphere, combined with current climate model outlooks, suggest the likelihood of La Niña forming in 2016 has increased to around 50%. As a result, the Bureau's ENSO Outlook status has moved to La Niña WATCH.

Temperatures below the Pacific Ocean surface have declined since late 2015, with all but the top 50 metres now cooler than normal. At the sea surface, temperatures have cooled by over 1 °C since their peak, but remain warmer than average and still at El Niño levels. The Southern Oscillation Index and trade winds also show clear signs that El Niño is in decline. The SOI has recently risen to near-neutral levels, while trade winds are near normal. However some indicators, such as cloudiness near the Date Line, have shown only a limited shift away from El Niño patterns.

International climate models suggest El Niño will continue to weaken during the southern autumn, returning to neutral levels by mid-2016. By spring, five of the eight surveyed models suggest La Niña is likely, with three remaining neutral. ENSO forecasts made at this time of year tend to have lower accuracy than at other times, with a clearer picture to emerge over the coming months.

La Niña is often, but not always, associated with above-average winter-spring rainfall over northern, central and eastern Australia.

Australia's climate is also being influenced by record warm temperatures in the Indian Ocean. The warmth in the Indian Ocean will likely provide extra moisture for rain systems as they cross Australia during the southern autumn.

During March, equatorial cloudiness near the Date Line has mostly been above average (negative outgoing longwave radiation anomalies). Recent values seen in April have been closer to the long-term average, but are still currently above average. Cloudiness near the Date Line has mostly been above average since March last year.

Cloudiness along the equator near the Date Line typically increases during El Niño (below average outgoing long-wave radiation, or OLR) and decreases during La Niña (above average OLR).

Trade winds for the 5 days ending 10 April remain broadly close to normal across the equatorial Pacific Ocean.

The return to near-normal trade winds is consistent with a declining El Niño. Trade winds were consistently weaker than average, and on occasion reversed in direction (i.e. westerly rather than easterly), from the start of 2015 through to January 2016.

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.

Climate models suggest the El Niño will continue to weaken during the southern autumn and winter months.

By the end of winter, five of eight models suggest La Niña is likely, with three models suggesting neutral conditions. Heading into the traditional autumn ENSO transition period and with model skill generally low at this time of year, subsequent model outlooks will be monitored closely.

The SST (sea surface temperature) anomaly map for March 2016 shows positive SST anomalies extend across the central and eastern equatorial Pacific. Compared to February, positive anomalies have decreased along the equator, but have increased around Australia, both continuing a trend observed since late 2015, and typical of El Niño decay.

March values show the NINO3 region in the eastern Pacific cooled by 0.1 °C and the NINO3.4 region cooled by 0.4 °C over the past month, continuing the cooling trend initiated in late 2015. Values in the Bureau dataset for NINO3, NINO3.4 and NINO4 were +1.5 °C, +1.5 °C and +1.2 °C respectively.

Positive anomalies persist and have increased over much of the Indian Ocean compared to February.

The current 30-day Southern Oscillation Index (SOI) is −7.5 (10 April), which just exceeds the El Niño threshold of −7.

Fluctuations of the SOI during Australia's northern wet season (October-April) are not unusual as the passage of tropical systems near Darwin and Tahiti affects atmospheric pressure. During this period, the SOI should be used cautiously; 90-day values can provide more reliable guidance. The current 90-day SOI is −13.4, with this value having decreased since the start of March, reflecting the general decline in El Niño conditions.

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 10 April was −0.16 °C. The IOD does not typically influence Australian climate during the months December to May, when the monsoon trough is in the southern hemisphere (as positive and negative events are typically unable to form in monsoonal flow).

Currently four of five international models monitored by the Bureau clearly indicate negative IOD conditions are possible by August, with the fifth very close to negative IOD levels. However, model skill is generally lower at this time of year, and outlooks, particularly towards the end of the forecast period, should be used with caution.

Sea surface temperatures (SSTs) remain significantly warmer than average across the tropical Indian Ocean.

The four-month sequence of sub-surface temperature anomalies to March shows a cooling trend in the warm sub-surface temperature anomalies in the central and eastern Pacific.

During March, warm anomalies were present in the top 50 m of the equatorial Pacific sub-surface, extending between about 170° E and the South American coastline. These anomalies have continued to cool since November. Cool anomalies, around 100 m below the surface now extend from the western Pacific to approximately 100° W.

The sub-surface temperature map for the 5 days ending 10 April show that the Pacific sub-surface is now largely cooler than average. Only a small area in the top 50 m remains more than 1 °C warmer than average.

The volume of cooler than average water has progressively moved eastwards over the past few weeks, and is expected to continue. The surface of the equatorial Pacific is likely to cool as a result in the coming weeks, in line with the expected return to ENSO-neutral by mid-year.