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

SSTs for August 2022 were cooler than average along the equator from around 160°E to around 110°W, and warmer than average around the Maritime Continent in the west and off the coast of South America in the east.

Compared to July, cool anomalies have strengthened in the eastern tropical Pacific, while warm anomalies persist in the west.

Values of the three key NINO indices for August 2022 were: NINO3 −0.2 °C, NINO3.4 −0.7 °C, and NINO4 −0.6 °C.

For the week ending 11 September 2022, sea surface temperatures (SST) in the tropical Pacific Ocean were cooler than average along much of the equator between 160°E and 95° W. Cool SST anomalies extend south of the equator in much of the central and eastern Pacific. A small area of warm anomalies remains in the eastern equatorial Pacific, between 95°W and the South American coastline. Warm SST anomalies continue over the Maritime Continent and around much of Australia.

Compared to two weeks ago, cool SST anomalies have strengthened in the central equatorial Pacific Ocean, while warm anomalies have generally increased to Australia's north.

The latest values of the three NINO indices for the week ending 11 September 2022 were: NINO3 −0.6 °C, NINO3.4 −0.8 °C, and NINO4 −0.7 °C.

Persistent NINO3 or NINO3.4 values cooler than −0.8 °C are typical of La Niña, while persistent values warmer than +0.8 °C typically indicate El Niño.

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 11 September 2022 was +10.5. The 90-day SOI value was +12.5.

Both the 30-day and 90-day SOI have risen slightly over 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 +7 and −7 generally indicate neutral conditions.

Trade winds for the 5 days ending 11 September 2022 were stronger than average west of the International Date Line and for parts of the eastern Pacific.

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

The Madden–Julian Oscillation (MJO) signal has been weak during since the beginning of September and is likely to remain weak for at least the coming seven days. A weak or indiscernible MJO has little influence on Australian climate.

A negative Indian Ocean Dipole is under way. The latest Indian Ocean Dipole (IOD) index value, for the week ending 11 September 2022, was −0.79 °C. The IOD index value has been at or below the negative IOD threshold (−0.4 °C) since June.

Cool anomalies are present in the north-west of the Indian Ocean basin close to the Horn of Africa, while weak warm SST anomalies continue across the east of the Indian Ocean, including in waters close to Indonesia and north-west Australia.

A negative IOD increases the chances of above average spring rainfall for most of the eastern two thirds of Australia. It also increases the chances of warmer nights for northern Australia, and cooler days for much of the eastern mainland.

All five international climate models surveyed indicate a negative IOD event is likely to persist until at least the end of spring. A negative IOD increases the chance of above average winter and spring rainfall across much of Australia.

Cloudiness near the Date Line had been mostly below average (i.e. positive outgoing longwave radiation, or OLR, anomalies) since June 2021.

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

The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to September 2022) shows cool anomalies from the surface to almost 200 m depth in the central to eastern equatorial Pacific. Warm anomalies persist between around 100 m and 250 m depth west of the International Date Line.

Cool anomalies increased in the central to eastern equatorial Pacific sub-surface month-on-month across winter.

For the five days ending 12 September 2022, sub-surface temperatures along the equator were mostly within 2 ºC of average. Compared to two weeks ago, cool anomalies in the eastern sub-surface expanded and strengthened, while the warm anomalies in the west contracted slightly. In the west, temperatures were more than two degrees warmer than average from around 125 m and 150 m depth between 160 °E and 175 °E, and in the east, temperatures were more than three degrees cooler than average around 125 m depth at 140 °W.

The Bureau's ENSO Outlook has been raised to LA NIÑA.

Key atmospheric and oceanic indicators of the El Niño–Southern Oscillation (ENSO) show an established La Niña. Tropical Pacific sea surface temperatures have been cooling since June and are now at La Niña thresholds. Atmospheric indicators including the Southern Oscillation Index (SOI), trade wind strength, and equatorial cloudiness are also displaying patterns typical of a La Niña event.

Models indicate this La Niña event may peak during the spring and return to neutral conditions early in 2023. La Niña events increase the chances of above-average rainfall for northern and eastern Australia during spring and summer.

The negative Indian Ocean Dipole (IOD) event continues. The IOD index has satisfied negative IOD thresholds (i.e. at or below −0.4 °C) since June, with the latest weekly value being −0.8 °C. All surveyed climate models agree that negative IOD conditions are likely to continue into late spring. A negative IOD event is typically associated with above average spring rainfall for much of Australia. When a La Niña and negative IOD combine, it further increases the likelihood of above average rainfall over Australia, particularly in the eastern half of the continent.

The Southern Annular Mode (SAM) is currently in a positive phase and is likely to be mostly positive for the coming three months. During the spring months, a positive SAM has a wetting influence for parts of eastern New South Wales and far eastern Victoria, but a drying influence for western Tasmania.

The Madden–Julian Oscillation (MJO) continues to show a weak signal with most models suggesting it will remain weak for at least the next seven days. A weak MJO is unlikely to have much impact on Australian climate.

Climate change continues to influence Australian and global climate. Australia's climate has warmed by around 1.47 °C for the 1910–2020 period. Southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades. There has also been a trend towards a greater proportion of rainfall from high intensity short duration rainfall events, especially across northern Australia.

The Southern Annular Mode (SAM) index is currently positive, and it is likely to remain positive throughout much of spring.

A positive SAM during spring typically increases the chance of below-average rainfall in western Tasmania and above-average rainfall in eastern parts of New South Wales and Victoria and south-eastern Queensland.

A La Niña event is under way in the tropical Pacific and the Bureau's ENSO Outlook has shifted to La Niña.

All seven surveyed international climate models show NINO indices are expected to meet or exceed La Niña thresholds by October, with five persisting at these levels until at least the end of 2022. Most models indicate a return to ENSO-neutral conditions in early 2023, suggesting a relatively short-lived event; ENSO events typically decay during the southern hemisphere autumn.

While back-to-back La Niña events are not uncommon, and have occurred in approximately half of all past events since 1900, three La Niña events in a row is less common and has previously occurred only three times in the Bureau record since 1900: 1954–57, 1973–76, and 1998–2001.