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

For the week ending 26 February, sea surface temperatures (SSTs) in the equatorial Pacific Ocean are generally close to average. However, anomalies greater than +1 °C are present in the far eastern Pacific.

Areas of warm SST anomalies also persist in the western Pacific, particularly around eastern Australia, and also across much of the Pacific south of the equator.

All NINO regions have warmed over the past fortnight; NINO3.4 by 0.3 °C, NINO3 by 0.1 °C, and NINO4 by 0.2 °C. The NINO3 SST anomaly for the week ending 26 February was +0.6 °C, while NINO3.4 had a weekly value of +0.2 °C. This is the first time since June 2016 that no NINO indices have had negative (cool) values.

The El Niño-Southern Oscillation (ENSO) remains neutral. However, recent changes in both the tropical Pacific Ocean and atmosphere, and climate model outlooks surveyed by the Bureau, suggest the likelihood of El Niño forming in 2017 has risen. As a result, the Bureau's ENSO Outlook status has been upgraded to El Niño WATCH, meaning the likelihood of El Niño forming in 2017 is approximately 50%.

All atmospheric and oceanic indicators of ENSO are currently within neutral thresholds. However, sea surface temperatures have been increasing in the eastern Pacific Ocean and are now warmer than average for the first time since June 2016, while the Southern Oscillation Index (SOI) has been trending downwards.

Seven of eight international models surveyed by the Bureau indicate steady warming in the central tropical Pacific Ocean over the next six months. Six models suggest El Niño thresholds may be reached by July 2017. However, some caution must be taken at this time of year, with lower model accuracy through the autumn months compared to other times of the year.

El Niño is often associated with below average winter–spring rainfall over eastern Australia and warmer than average winter–spring maximum temperatures over the southern half of Australia.

The Indian Ocean Dipole (IOD) has little influence on Australia from December to April. Current outlooks suggest a neutral IOD may persist until the end of autumn.

Cloudiness remains below average near the Date Line. Cloudiness has been generally below average since the start of August 2016.

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

Trade winds for the 5 days ending 26 February were near average over the eastern half of the tropical Pacific, and stronger than average west of the Date Line along and just south of the equator. Trade winds have been generally close to average since autumn 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 surveyed by the Bureau indicate that the central Pacific will continue to warm with ENSO-neutral conditions likely for the southern hemisphere autumn. From June onwards this warming is forecast to approach or surpass El Niño thresholds.

Six of the eight models suggest El Niño thresholds will be reached during July 2017. However, it should be noted that model outlooks that span the southern autumn period tend to have lower accuracy than outlooks issued at other times of the year. This means outlooks beyond May should be used with some caution.

SST anomalies for January show the equatorial Pacific Ocean is close to average. In the far western Pacific Ocean, SSTs are weakly warmer than average.

Large areas of the southern half of the Pacific Ocean remain warmer than average. Closer to Australia, SSTs are warmer than average surrounding southeast and eastern Australia, while in the west, SSTs are close to average.

The January values for the NINO3, NINO3.4 and NINO4 regions are 0.0 °C, −0.3 ° and −0.1 °, respectively, all well within ENSO-neutral levels.

The 30-day Southern Oscillation Index (SOI) to 26 February is −1.2 (90 day value +0.4). SOI values have generally been within the neutral range since mid-October.

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 index value to 26 February was +0.11 °C.

The influence of the IOD on Australian climate is weak during December to April. This is due to the monsoon trough shifting south over the tropical Indian Ocean and changing the overall wind circulation, which in turn prevents an IOD ocean temperature pattern from being able to form. Current outlooks suggest a neutral IOD for the end of autumn.

The four-month sequence of sub-surface temperature anomalies (to 23 February) shows cooler than average water across the sub-surface of the central to eastern equatorial Pacific Ocean. The strength of these cool anomalies has strengthened in the past month, compared to January, but has generally been weakening and decreasing in volume since September.

The areal extent and magnitude of weak warm anomalies present in the top 100 m of the tropical Pacific in areas west of the Date Line has also increased slightly compared to January, however remains generally weak and has decreased since late 2016.

The sub-surface temperature map for the 5 days ending 27 February shows waters are generally close to average across the sub-surface of the equatorial Pacific Ocean. Five-day anomalies greater than +2 °C are present in a small area of the western Pacific subsurface at 150 m depth near the Date Line. Weak warm anomalies of this size have been fairly stable in this position for the past month.