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

Sea surface temperatures (SSTs) in the central tropical Pacific Ocean are within the ENSO-neutral range, but remain slightly cooler than average along parts of the central equatorial Pacific.

SSTs in the western Pacific remain warmer than average. Compared to two weeks ago, warm anomalies have strengthened in large areas to the northwest of Australia. Warm anomalies also persist around Australia's eastern seaboard, and around South East Asia, and are more than 1 °C warmer than average for the week ending 28 August in large areas.

Areas of warm SST anomalies have continued to decrease in the eastern Indian Ocean as the negative Indian Ocean Dipole (IOD) event eases back towards neutral, but remain well developed between the northwest of Australia and Indonesia. Cool anomalies in the western Indian Ocean—off Africa—had already dissipated at the time of the previous ENSO Wrap-Up.

In the tropical Pacific Ocean, the El Niño—Southern Oscillation (ENSO) remains neutral, but a late and weak La Niña remains possible. In the Indian Ocean, a negative Indian Ocean Dipole (IOD) continues, but has weakened from record July index values.

International climate models surveyed by the Bureau suggest the negative IOD will weaken during the southern hemisphere spring, and is likely to end in November. This means its influence on Australia’s spring rainfall may not be as strong as it has been during this winter, when wetter conditions prevailed in the east.

In the tropical Pacific Ocean, sea surface temperatures are cooler than average, though remain well short of La Niña levels. In the atmosphere, there has been little change in trade winds or cloudiness, indicating little or no coupling between the atmosphere and ocean. As a result, cool sub-surface temperatures have eased slowly towards normal. International climate models suggest neutral to weak La Niña levels for the remainder of the year. A La Niña WATCH remains in place.

During La Niña, northern and eastern Australia typically experience above average spring rainfall, with the first rains of the wet season typically arriving earlier than normal in northern Australia. Some La Niña-like effects can still occur even if thresholds are not exceeded.

Cloudiness near the Date Line has been generally below average for most of August.

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

Trade winds near the equator in the Pacific Ocean have remained close to average for the 5 days ending 28 August, and have remained generally so since March.

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.

Outlooks from the eight international climate models surveyed by the Bureau continue to show some mixed projections. There is significant variation between models and a generally wide spread in ensemble members within each model. Three of the surveyed models indicate a late-forming La Niña is likely to develop late during the southern hemisphere spring or during summer, while the other five indicate neutral ENSO conditions are the more likely outcome for the outlook period.

A late forming La Niña would be unusual but not unprecedented.

If La Niña does form, models suggest it will be weak, potentially short-lived, and well below the strength of the significant 2010–12 event.

SSTs for July 2016 were cooler than average in a narrow band along the equator in the eastern and central Pacific, having strengthened compared to June. SSTs were warmer than average both north and south of the equator in the eastern half of the tropical Pacific, and across most of the western half of the tropical Pacific, around Australia, and extending to Indonesia and South East Asia. Large areas around Australia's east coast and between Australia and Indonesia were more than 1 °C warmer than average.

The July vlaues for the NINO3 and NINO3.4 regions were both −0.3 °C, which was 0.3 °C cooler than June for NINO3.4 and 0.2 °C cooler for NINO3. NINO4 also cooled compared to the previous month, but remained warmer than average at +0.4 °C.

The latest 30-day Southern Oscillation Index (SOI) to 28 August 2016 is +4.9, within the neutral ENSO range. The 30-day SOI had dropped as low as +2.5 during the past fortnight.

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 negative Indian Ocean Dipole (IOD) event continues. Although cool anomalies have eased back to average in the western Indian Ocean, and warm anomalies have declined in some parts of the eastern Indian Ocean, an are of significantly warmer than average water remains south of Indonesia and to the northwest of Australia. The weekly index value to 28 August was −0.69 °C.

The Indian Ocean Dipole (IOD) index has been below the −0.4 °C negative IOD threshold for fourteen weeks, peaking at −1.37 °C in early July. The July 2016 monthly IOD index value reported in the ERSSTv4 dataset was the strongest negative value in at least 50 years of record.  

International climate models indicate the negative IOD will continue to steadily weaken during spring as is typical of the lifecycle of IOD events. This means its influence on Australian rainfall may lessen in the coming months.

A negative IOD typically brings above average rainfall to southern Australia during winter–spring, cooler than normal daytime temperatures to southern Australia, and warmer daytime and night-time temperatures to northern Australia.

The four-month sequence of sub-surface temperature anomalies (to 25 August) shows cool anomalies span the entire width of the equatorial Pacific Ocean, although temperatures in the top 50 m of water west of 170° W was slightly warmer than average. Compared to July these warm anomalies have strengthened, while the pattern of cool anomalies remains similar.

The sub-surface temperature map for the 5 days ending 28 August shows temperatures generally close to average across the sub-surface of the equatorial Pacific. Compared to two weeks ago cool anomalies in the central equatorial Pacific have weakened significantly, although an area of water remains slightly cooler than average between 140° W and 175° W around 150 m depth. This warming is largely due to only limited coupling of the ocean and atmosphere, and hence lack of enhanced trade winds which draw cooler water up from the deep.