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

The August monthly SST map shows cooler than average SSTs along much of the equator in the central and eastern tropical Pacific Ocean. Cool anomalies also extend south of the equator along the South American coast. Warmer than average SSTs in the western equatorial Pacific and in the Tasman Sea generally strengthened compared to July.

The August values of the three key NINO indices were: NINO3 −0.4 °C, NINO3.4 −0.4 °C, and NINO4 −0.1 °C.

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 27 September was +10.4. The 90-day SOI value is also above La Niña thresholds at +8.1.

Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.

Trade winds for the 5 days ending 27 September were stronger than average over the western tropical Pacific. More generally, Pacific trade winds have been stronger than average in recent months.

During El Niño there is a sustained weakening, or even reversal, of the trade winds across much of the tropical Pacific. Conversely, during La Niña, there is a sustained strengthening of the trade winds.

The Madden-Julian Oscillation (MJO) is weak or indiscernible, but may increase in strength as it moves from the Maritime Continent into the Western Pacific Ocean.

Large parts of the central and eastern Indian Ocean are warmer than average, with surface temperatures close to average in much of the west of the basin. The latest weekly value of the Indian Ocean Dipole (IOD) index to 27 September was −0.45 °C, returning again to negative dipole values.

Five of the six surveyed climate models indicate values indicate the IOD will be negative in October, and three continue the event into November. To be considered an official negative IOD event we will need to see values of the IOD index remain at or cooler than −0.4 °C for eight weeks.

A negative IOD typically brings above average spring rainfall to most of the eastern two thirds of Australia and to south-east Western Australia.

Cloudiness near the Date Line was below average over the past fortnight and has generally been below average since early to mid-March.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies). 

The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to 24 September) shows cooler than average water extending across the top 200 m of the sub-surface of the equatorial Pacific east of the Date Line.  The strength and extent of cooler than average water has increased month-on-month compared to both August and July.

Weak warm anomalies persist across large parts of the column depth in the western equatorial Pacific. 

For the five days ending 27 September, sub-surface temperatures were cooler than average in the central to eastern equatorial Pacific between 50 and 150 m. These cool anomalies have strengthened compared to two weeks ago, reaching more than 4 degrees cooler than average in a small volume around 140°W. Temperatures are close to average in the sub-surface of the western equatorial Pacific Ocean. 

The Bureau’s ENSO Outlook has moved to LA NIÑA, indicating La Niña is established in the tropical Pacific. All surveyed international climate models indicate this La Niña will persist until at least January 2021.

While models agree La Niña will continue well into summer 2020–21, around half the models predict a strong event, while 3 of 8 models suggest moderate strength. Overall, models do not currently anticipate this event will be as strong as the La Niña of 2010–12, which was one of the four strongest La Niñas on record. The strength of La Niña impacts on Australia are often related to the strength of the event.

Central and eastern tropical Pacific Ocean sea surface temperatures exceed La Niña thresholds (0.8 °C below average) and atmospheric indicators, including the Southern Oscillation Index (SOI), trade winds and cloud, are also at La Niña levels.

In the Indian Ocean, the latest values of the Indian Ocean Dipole (IOD) index have again gone into negative dipole territory. Five of the 6 surveyed models indicate the IOD will be negative for October, and three models continue negative IOD values into November.

Both La Niña and negative IOD typically increase the chance of above average rainfall across much of Australia during spring. Above average summer rainfall is also typical across eastern Australia during La Niña. Current climate outlooks indicate the remainder of 2020 will be wetter than average across the eastern two thirds of Australia.

The Southern Annular Mode (SAM) is expected to be neutral or weakly positive for the coming weeks. La Niña tends to favour positive SAM during spring and summer, which typically enhances the wet signal in the east.

The Madden–Julian Oscillation (MJO) is currently weak or indiscernible, but may increase in strength as it moves from the Maritime Continent into the Western Pacific Ocean.

Climate change is also influencing the Australian climate. Australia's climate has warmed by around 1.4 °C since 1910, while southern Australia has seen a 10–20% reduction in cool season (April–October) rainfall in recent decades.

The Southern Annual Mode (SAM) is expected to be neutral or weakly positive over the first three weeks of October. A positive SAM during spring is typically associated with wetter and cooler than average conditions in parts of eastern Australia.

All of the international climate models surveyed by the Bureau indicate central tropical Pacific sea surface temperatures in the NINO3.4 region will continue to cool over the coming months. All eight models indicate this La Niña will persist until at least January 2021. Most models reach their peak in December, and five maintain the event into February.

ENSO events—El Niño or La Niña—typically begin to develop during the southern hemisphere autumn to winter, before strengthening in winter to spring.

La Niña increases the likelihood of above average rainfall across much of Australia during spring, and across much of eastern Australia during summer. La Niña increases the chance of cooler than average daytime temperatures for large areas. It also increases the chance of tropical cyclones, and earlier first rains of the northern wet season.