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

For the week ending 9 May, sea surface temperatures (SSTs) in the central to western equatorial Pacific Ocean were close to average. Weakly warm SST anomalies persist across much of the South Pacific, including areas immediately south of the equator. Warm anomalies greater than +1 °C were present in the eastern Pacific off the South American coast.

The NINO3.4 SST anomaly for the week ending 9 May was +0.5 °C, with NINO3 at +0.5 °C and NINO4 at +0.3 °C.

The tropical Pacific is currently El Niño–Southern Oscillation (ENSO) neutral. Despite the likelihood for El Niño easing in some models, an event in 2017 cannot be ruled out. The Bureau's ENSO Outlook remains at El Niño WATCH, meaning there is around a 50% chance that El Niño may develop in the coming months.

Sea surface temperatures in the tropical Pacific Ocean have warmed since the start of the year, but remain below El Niño thresholds. Some other atmospheric indicators have shifted over the past fortnight, but also remain below El Niño levels.

Some international climate models have reduced the likelihood of El Niño this year compared to last month. However, five of eight international climate models still indicate the tropical Pacific Ocean may exceed El Niño thresholds during the second half of 2017. It should be noted that models have lower accuracy forecasting El Niño through the autumn months.

El Niño is often, but not always, associated with a drier than average winter-spring over eastern Australia. Of the 27 El Niño events since 1900, 18 have resulted in at least some areas of significantly dry conditions for Australia.

The Indian Ocean Dipole (IOD) remains neutral. Four out of six climate models suggest a positive IOD is likely to develop during winter. Generally, when a positive IOD coincides with El Niño, the pattern of below average rainfall extends further west than it typically would under El Niño alone.

Cloudiness near the Date Line is close to average after briefly being above average for the first time since winter 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 7 May were close to average over most of the tropical Pacific. A strong reversal of the trade winds can be seen in the western Pacific, the result of tropical cyclone Donna. As these winds are likely to be only shortlived, they are unlikely to have a significant effect on possible El Niño development.

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 is likely to continue to warm, with five of eight surveyed models indicating El Niño is likely to form by spring. However, the Bureau's climate model POAMA predicts that the Pacific will begin to cool in winter and remain neutral for the rest of the year.

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 April show sea surface temperatures in the central to western equatorial Pacific Ocean were close to average. Weak warm anomalies were present in the eastern Pacific, across much of the Pacific south of the equator, and in the far western Pacific around eastern Australia including Tasmania and New Zealand.

The April values for the NINO3.4, NINO3 and NINO4 regions were +0.3 °C, +0.6 °C and 0.1 °C, respectively.

The 30-day Southern Oscillation Index (SOI) to 7 May was −8.9 (90-day value −2.4). This is the most negative SOI value since May 2016.

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 7 May was +0.3 °C.

Current outlooks suggest a neutral IOD for the end of autumn, with some models indicating a positive IOD may form later in winter or spring. The Bureau's model POAMA predicts that the IOD will stay neutral for the remainder of the year.

A positive IOD typically brings below average winter-spring rainfall to parts of southern and central Australia.

The four-month sequence of sub-surface temperature anomalies (to 4 May) shows that the cooler than average sub-surface of the central to eastern equatorial Pacific Ocean has warmed in recent weeks, returning to near average temperatures, particularly in the central Pacific.

Areas of weak warm anomalies present in the top 150 m of the tropical Pacific west of 160 °E have also eased slightly and shifted eastwards.

The sub-surface temperature map for the 5 days ending 8 May shows temperatures were generally close to average across the sub-surface of the equatorial Pacific Ocean. In the western Pacific, there was a small area of weak warm anomalies at a depth of 100 to 150 m. In the shallow eastern Pacific there were weak warm anomalies to a depth of 50 m, while beneath this there were weak cool anomalies at a depth of 50 to 100 m; these cool anomalies have eased slightly over the past fortnight.