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, and anomalies greater than +2 °C near the South American coast.

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 cooled slightly over the past fortnight in response to strengthened trade winds in the eastern Pacific (due to the Madden-Julian Oscillation); NINO3 by 0.2 °C, and both NINO3.4 and NINO4 by 0.1 °C. The NINO3 SST anomaly for the week ending 12 March was +0.4 °C.

The El Niño-Southern Oscillation (ENSO) is neutral. However, model outlooks and recent warming in the Pacific Ocean mean there is an increased chance of El Niño forming later this year. The Bureau's ENSO Outlook is currently at El Niño WATCH, which means the likelihood of El Niño forming this year is around double the average chance at 50%.

Most atmospheric and oceanic indicators of ENSO are currently neutral. However, sea surface temperatures (SSTs) in the eastern Pacific Ocean have warmed since the start of the year, and the Southern Oscillation Index (SOI) has been trending downwards. While these are fairly typical changes in the lead up to El Niño, trade winds and cloudiness have not shown any significant shift away from neutral.

All eight international models surveyed by the Bureau show steady warming of 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, as models have lower accuracy when forecasting through the autumn months than at other times of the year.

El Niño is often, but not always, 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 is likely to remain at least through to the end of winter.

Cloudiness remains below average near the Date Line. Cloudiness has been generally below average since the start of August 2016, likely a result of the location of the Madden-Julian Oscillation. 

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 12 March were near average over the eastern half of the tropical Pacific, and stronger than average west of 170°W. Trade winds have been stronger than average over the western tropical Pacific for the past fortnight.

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 February show the equatorial Pacific Ocean is close to average. Warm anomalies were present in the far eastern Pacific, across much of the Pacific south of the equator, and in the far western Pacific around eastern Australia and much of the Maritime Continent.

The February values for the NINO3, NINO3.4 and NINO4 regions were +0.5 °C, 0.0 ° and −0.1 °, respectively.

The 30-day Southern Oscillation Index (SOI) to 12 March is −5.1 (90 day value +0.9). 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 12 March was −0.14 °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 February) shows cooler than average water across the sub-surface of the central to eastern equatorial Pacific Ocean. These cool anomalies have strengthened compared to January, but have 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 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 12 March shows waters are generally close to average across the sub-surface of the equatorial Pacific Ocean.