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

SSTs for September 2022 were cooler than average across the central and eastern tropical Pacific Ocean, extending from around 160°E to the South American coastline and also extending across a large area south of the equator, particularly in the east of the basin.

A small area of very weak warm anomalies was present along the equator close to the South American coastline, and stronger warm anomalies were observed across much of the Maritime Continent and around northern Australia. Warm anomalies extend into the mid-latitudes in the southern Pacific and across the mid- to high latitudes in the north—a pattern characteristic of well-developed La Niña.

Compared to August, cool anomalies have generally strengthened, while warm anomalies maintained mostly similar strength.

Values of the three key NINO indices for September 2022 were: NINO3 −0.6 °C, NINO3.4 −0.8 °C, and NINO4 −0.7 °C.

For the week ending 9 October 2022, sea surface temperatures (SST) were cooler than average along much of the equator in the central and eastern tropical Pacific Ocean, between 160°E and 90°W. Cool SST anomalies are strongest to the south of the equator, and extend across a large area of the central and eastern Pacific and along much of the South American coastline. This off-equatorial focus of cool anomalies is reflected in the difference shown in the two sub-surface plots; the 5-day plot samples anomalies 2° either side of the equator, and the monthly plot samples anomalies 5° either side of the equator.

Warm SST anomalies continue in the far west of the Pacific, with weak anomalies over the Maritime Continent, and stronger anomalies around much of northern Australia.

Compared to two weeks ago, cool SST anomalies have strengthened slightly in the central and eastern equatorial Pacific Ocean, while warm anomalies have decreased in the west of the Pacific basin.

The latest values of the three NINO indices for the week ending 9 October 2022 were: NINO3 −0.6 °C, NINO3.4 −0.6 °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 9 October 2022 was +19.2. The 90-day SOI value was +13.4.

The 30-day SOI value has remained similar over the past fortnight, while the 90-day value has risen slightly.

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 9 October 2022 were stronger than average across the western half of the tropical Pacific Ocean.

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 was weak for most of September and early October. However, most models indicate a pulse of the MJO is likely developing over the Maritime Continent, and will maintain moderate strength as it moves eastwards into the western Pacific over the coming one to two weeks.

While active in the Pacific at this time of the year, the MJO slightly increases the chance of above average rainfall over the eastern half of Australia, and may weaken the trade winds over the tropical Pacific.

A negative Indian Ocean Dipole is under way. The latest Indian Ocean Dipole (IOD) index value, for the week ending 9 October 2022, was −0.57 °C. The IOD index value has been at or below the negative IOD threshold (−0.4 °C) since June.

Small areas of cool anomalies are present in the north-west of the Indian Ocean basin close to the Horn of Africa, while areas of 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 international climate models surveyed by the Bureau indicate a negative IOD event is likely to persist until the end of spring. Only one model meets the IOD threshold in December, with all models indicating a rapid decline of IOD index values across the remainder of spring. IOD events typically breakdown in late spring or early summer with the arrival of the Asian monsoon.

Cloudiness near the Date Line had been mostly below average (i.e. positive outgoing longwave radiation (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 around 150 m depth in the central to eastern equatorial Pacific. In parts of this region east of 140°W anomalies reached more than 3 degrees cooler than average.

Warm anomalies persist between around 100 m and 250 m depth west of the International Date Line. In parts of this region anomalies reached more than 3 degrees warmer than average west of 160°E.

The pattern and strength of anomalies in September is similar to those observed in August.

For the five days ending 9 October 2022, sub-surface temperatures were slightly warmer than average in the western equatorial Pacific, reaching more than 2 degrees warmer than average between around 125 and 175 m depth, west of 170°W. Sub-surface temperatures were mostly within 2 degrees of average across the remainder of the basin, but in the east cool anomalies exceeding 2 degrees cooler than average were observed in a region between around 150°W and 125°W and around 100 to 150 m depth.

Compared to two weeks ago, cool anomalies in the eastern sub-surface have increased while warm anomalies in the west showed little change.

The off-equatorial focus of cool anomalies is reflected in the difference shown in the two sub-surface plots; the 5-day plot samples anomalies 2° either side of the equator, and the monthly plot samples anomalies 5° either side of the equator.

La Niña continues in the tropical Pacific, and is likely to persist into early 2023.

Both atmospheric and oceanic indicators of the El Niño–Southern Oscillation (ENSO) are consistent with an established La Niña, including tropical Pacific sea surface temperatures, the Southern Oscillation Index (SOI), trade wind strength, and equatorial cloudiness.

Models indicate the La Niña is likely to decline over spring, with a return to ENSO-neutral conditions (neither La Niña nor El Niño) early in 2023. Sea surface temperatures in the tropical Pacific remain similar, compared to two weeks ago. The SOI remains well above La Niña thresholds.

La Niña typically increases the chance of above average rainfall for northern and eastern Australia during spring and summer.

The negative Indian Ocean Dipole (IOD) event also continues. The IOD index has satisfied negative IOD thresholds (i.e. at or below −0.4 °C) since June. Models indicate that the negative IOD is likely to persist until late spring. A negative IOD typically increases the chance of above average spring rainfall for most of the eastern two thirds of Australia.

The Southern Annular Mode (SAM) is currently in a positive phase and is likely to remain generally positive throughout spring into early summer. During the spring and summer months, a positive SAM increases the chance of above average rainfall for parts of eastern New South Wales, eastern Victoria, and south-eastern Queensland, and increases the chance of below average rainfall for western Tasmania.

The MJO is moving into the western Pacific Ocean and is forecast to strengthen further in the coming fortnight as it tracks further east. Its influence at this time of the year may lead to above-average rainfall for parts of eastern Australia, and briefly reduce the strength of equatorial trade winds west of the Date Line.

When La Niña and negative IOD conditions combine, the likelihood of above average rainfall over Australia is further increased, particularly for the eastern half of the continent. The Bureau of Meteorology's extended and long-range forecasts show that above average rainfall is likely across much of eastern Australia. This reflects the influence of several key climate drivers.

Climate change continues to influence Australian and global climate. Australia's climate has warmed by around 1.47 °C for the 1910–2020 period. 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 in a positive phase, and it is likely to remain positive throughout spring and early summer.

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 continues at LA NIÑA.

All seven surveyed international climate models anticipate central Pacific sea-surface temperatures will meet or exceed La Niña thresholds (−0.8 °C) during October, with five continuing close to or above the threshold in December. All but one model indicates a return to ENSO-neutral conditions in early 2023, suggesting a relatively short-lived event; ENSO-events typically decay during the southern hemisphere autumn.

La Niña events increase the chance of above-average rainfall for northern and eastern Australia during spring and summer.