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

For the week ending 12 February 2017, sea surface temperatures (SSTs) in the equatorial Pacific Ocean are generally close to average. However, anomalies greater than +1 °C have emerged over recent weeks in the far eastern Pacific.

Warm SST anomalies remain present in the western Pacific, particularly around east and southeast Australia, and also across much of the Pacific south of the equator.

The past fortnight has seen the NINO3 region warm by 0.5 °C, coming in at +0.5 °C for the week ending 12 February, while NINO3.4 has warmed by 0.2 °C, with a weekly value of −0.1 °C.

The El Niño–Southern Oscillation (ENSO) remains neutral, with virtually all indicators close to their average values. In recent weeks, the central and eastern tropical Pacific Ocean has shown surface warming, and climate models suggest this warming is likely to continue during the southern autumn. In marked contrast to last year, western Pacific sub-surface temperatures are up to 5 °C warmer than at the same time last year, indicating La Niña-like conditions are unlikely in 2017.

As this is the time of year when ENSO and climate models have greatest variability, some caution must be taken when using recent conditions, such as central Pacific warming, to determine likely conditions in winter. Hence either neutral or El Niño are considered the most likely ENSO state for the southern winter and spring.

El Niño is often associated with below-average rainfall during the second half of the year across large parts of southern and inland eastern Australia. Daytime temperatures also tend to be above average over southern Australia.

The Indian Ocean Dipole (IOD) is typically too weak to have a significant influence on the Australian climate from December to April. Model outlooks indicate a neutral IOD is likely through late autumn and early winter.

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 12 February 2017 were near average over the eastern half of the tropical Pacific, and weakly stronger than average in the western tropical Pacific. Trade winds are likely to weaken over the western tropical Pacific in the coming days, associated with the passage of the Madden–Julian Oscillation (MJO) over the Pacific Ocean. 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 ENSO-neutral conditions are most likely for the remainder of the southern hemisphere summer and into autumn. However, all models indicate the central Pacific is likely to warm over the coming months, with some reaching El Niño thresholds in winter. This suggests ENSO-neutral or El Niño are the most likely scenarios for the second half of 2017.

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 12 February 2017 is +1.0 (90 day value +3.3). 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 29 January is +0.05 °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 (ending January) shows cooler than average water across the sub-surface of the central to eastern equatorial Pacific Ocean. This cooler water has been progressively warming and shrinking in volume since September.

Weak warm anomalies have persisted in the top 100 m of the tropical Pacific in areas west of the Date Line; however, the areal extent and magnitude of these anomalies has decreased during January.

The sub-surface temperature map for the 5 days ending 12 February 2017 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 the western Pacific subsurface at 150 m depth. At this time in 2016, the same region was displaying anomalies of −3 °C, indicating that the current ocean ENSO precursors are considerably different this year.