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 neutral ENSO range, but remain slightly cooler than average, and have cooled slightly in parts of the central equatorial Pacific during the past fortnight.

SSTs in the western Pacific remain warmer than average. Although smaller than two weeks ago, large areas of water around northern Australia, Australia's eastern seaboard, and South East Asia are more than 1 °C warmer than average for the week ending 14 August.

Warm SST anomalies in excess of 1 °C warmer than average also extend across areas of the eastern Indian Ocean, northwest of Australia between the Australian coast and Indonesia. Areas of cool anomalies in the northwest of the Indian Ocean basin have largely dissipated; this may indicate the negative Indian Ocean Dipole (IOD) event is shifting back toward neutral.

The tropical Pacific Ocean persists at neutral El Niño—Southern Oscillation levels. However, the possibility of a weak La Niña in 2016 remains. In the Indian Ocean, a negative Indian Ocean Dipole (IOD) continues, but has weakened in recent weeks. The current event peaked in July as the strongest negative IOD event recorded in at least 50 years of record.

Climate models indicate the negative IOD will continue to steadily weaken over the southern hemisphere spring. This means its influence on Australian rainfall may lessen in the coming months. Rainfall has been well above average for large parts of Australia since May 2016 – which is a typical rainfall pattern observed during negative IOD events. During negative IOD events, southern Australia typically experiences above average winter and spring rainfall and cooler than average daytime temperatures. Northern Australia often experiences warmer than usual day and night-time temperatures.

In the Pacific Ocean, only two of eight international climate models monitored by the Bureau indicate La Niña is likely to develop during the austral spring, with two more indicating a possible late-forming event in summer. The remaining models suggest neutral or near-La Niña conditions. A La Niña WATCH remains in place, but if La Niña does develop it is likely be weak.

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

Cloudiness near the Date Line has fluctuated around average since the beginning of May, with no strong ENSO pattern evident.

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 normal for the 5 days ending 14 August, and generally 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.

Two of the eight international climate models surveyed by the Bureau briefly meet La Niña thresholds in September before returning to neutral. A different two models meet thresholds by November, and maintain the event into early summer. During January, at the end of the current outlook period, an additional two models also reach threshold values.

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

If La Niña does form, models suggest it will be weak, 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 14 August 2016 is +4.5, which is well within the neutral ENSO range.

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 has weakened in recent weeks, with cool SST anomalies largely dissipating in the northwest of the Indian Ocean, although warm anomalies persist over eastern parts of the basin. The weekly index value to 14 August was −0.54 °C.

The Indian Ocean Dipole (IOD) index has been below the −0.4 °C negative IOD threshold for twelve weeks, peaking at −1.4 °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. 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 July) shows cool anomalies span the entire width of the equatorial Pacific Ocean, although temperatures in top 50 m of water west of 180° W was mostly close to average in July (a slight eastward expansion compared to June). The spatial extent of the cool anomalies has decreased slightly in both June and July, drawing back from the western boundary.

The sub-surface temperature map for the 5 days ending 14 August shows temperatures generally close to average in the top 100 m of the equatorial Pacific. Deeper in the water column, waters remain cooler than average at 100 m–200 m depth of the equatorial Pacific. Compared to two weeks ago cooler anomalies have strengthened slightly with the spatial pattern remaining similar.

A small area of water more than 3 °C cooler than average persists at between 150°W and 175°W at 100 to 150 m depth.