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

For the week ending 4 June, sea surface temperatures (SSTs) in the central to western equatorial Pacific Ocean were close to average, while areas of generally weak warm SST anomalies persist along the equator in the eastern Pacific. Warm anomalies are also present across much of the South Pacific, including areas immediately south of the equator, although these anomalies have decreased in magnitude over the past few weeks.

The NINO3.4 SST anomaly has remained at around +0.5 °C since mid-April, with NINO3 dropping to +0.4 °C this week for the first time since mid-March. NINO4 is currently at +0.4 °C.

The El Niño–Southern Oscillation (ENSO) remains neutral. The Bureau's ENSO Outlook remains at El Niño WATCH, meaning there is around a 50% chance of El Niño developing in 2017—double the normal likelihood. However several indicators have shown little or no increase for several weeks, suggesting El Niño development has stalled for now.

Sea surface temperatures across the tropical Pacific remain warmer than average, though cooling has occurred in some areas over recent weeks in response to stronger than average trade winds. The Southern Oscillation Index has also eased to near zero values. All other ENSO indicators also remain neutral.

Four of eight international climate models suggest tropical Pacific Ocean temperatures may exceed El Niño thresholds during the second half of 2017, down from seven of eight models that were forecasting a possible event in April. Virtually all models have reduced the extent of predicted ocean warming compared to earlier in the year, indicating that if El Niño forms, it is likely to be weak.

El Niño is often, but not always, associated with a drier than average winter and spring over eastern Australia. If the tropical Pacific remains warmer than average, but El Niño thresholds are not quite met, some El Niño-like effects are still possible.

The Indian Ocean Dipole (IOD) remains neutral. Four out of six climate models suggest a positive IOD will develop by the end of winter. A positive IOD is typically associated with a drier than average winter and spring for southern and central Australia.

Cloudiness near the Date Line is close to average. Values have been fluctuating around average for around two months.

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 4 June were close to average over most of the tropical Pacific, with trades slightly weaker than average just south of the equator in the western Pacific.

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 El Niño remains possible for the second half of 2017. Four out of the eight surveyed models forecast SSTs in the central Pacific will reach or exceed the El Niño threshold at some point during winter or spring. However, some models show considerable spread across their outlooks, with four models favouring neutral ENSO conditions and none favouring La Niña.

Historical accuracy of models is lowest in late autumn, but begins to improve for outlooks generated in June. 

SST anomalies for May show sea surface temperatures in the western half of the 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, Tasmania, and New Zealand. There has been a general cooling across all areas compared to April.

The May values for the NINO3.4, NINO3 and NINO4 regions were +0.5 °C, +0.5 °C and 0.3 °C, respectively.

The 30-day Southern Oscillation Index (SOI) to 4 June was −0.6 (90-day value −0.7), within neutral territory.

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 4 June was −0.08 °C.

Four of the six surveyed models indicate a positive IOD is likely to form during winter. However, model skill is low at this time of year, so caution should be exercised when using these forecasts.

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 May) shows water temperatures in the sub-surface of the equatorial Pacific Ocean are generally near average. Areas of weak warm anomalies persist in the top 150 m of the tropical Pacific west of 160°E, while in the eastern tropical Pacific an area of weak cool anomalies is present in the top 100 m between about 120°W and 100°W.

The sub-surface temperature map for the 5 days ending 4 June shows temperatures were generally close to average across the equatorial Pacific Ocean. In the eastern Pacific weak warm anomalies are apparent between the surface and a depth of 100 m, with little change compared to two weeks ago. Cool anomalies at a depth of 100 to 200 m in the central Pacific have again strengthened over the past fortnight, now reaching more than 4 degrees cooler than average for a small area.