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

SSTs for November 2021 show weak cool SST anomalies were present across most of the equatorial Pacific, while weak warm SST anomalies were largely present across the remainder of the basin west of 160°E, including around the Maritime Continent and northern Australia.

Values of the three key NINO indices for November 2021 were: NINO3 −0.5 °C, NINO3.4 −0.6 °C, and NINO4 −0.3 °C.

Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 5 December 2021 were cooler than average along the equator across most of the Pacific Ocean. Compared to two weeks ago, cool anomalies have strengthened in the eastern equatorial Pacific.

Weak warm SST anomalies continue over parts of the Maritime Continent, with stronger warm anomalies around northern Australia. Compared to two weeks ago, warm anomalies have increased to the north-west of Australia but decreased across the Maritime Continent.

SSTs in the eastern half of the equatorial Pacific have cooled further over the past fortnight, moving NINO3 into La Niña values. The temperature gradient across the Pacific continues, with the characteristic cool tongue along the equator in the east and horseshoe-shaped pattern of warm SSTs anomalies in the west extending and surrounding these cool anomalies.

The latest values of the three NINO indices for the week ending 5 December 2021 were: NINO3 −0.8 °C, NINO3.4 −0.6 °C, and NINO4 −0.4 °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.

Trade winds for the 5 days ending 5 December 2021 were slightly stronger than average across parts of the central to the western tropical Pacific, and close to average in the eastern tropical Pacific. However, due to the sparsity of observations in the western half of the tropical Pacific confidence in current assessments is lower.

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) has moved in the western Pacific Ocean and has strengthened. The MJO is forecast to progress eastwards across the western Pacific over the coming fortnight, which increases the likelihood of above average cloudiness and rainfall across northern Australia and the western Pacific. It also increases the chance that the monsoon will develop in the Australian region in the next week or two—a little earlier than normal.

The latest weekly value of the Indian Ocean Dipole (IOD) index to 5 December 2021 was −0.34 °C, within neutral bounds.

While the IOD index values (which are ocean based) are within in the neutral range, a residual atmospheric pattern continues and warm SST anomalies persist in the east of the Indian Ocean basin. This pattern continues to weaken, with cloud patterns becoming more neutral over the past week.

All five international climate models surveyed by the Bureau indicate the IOD will remain neutral for the coming months, consistent with the typical life cycle of an IOD event. As the monsoon trough shifts south over the tropical Indian Ocean, it changes wind patterns and prevents an IOD event from forming. This is why IOD events are unable to form (and therefore influence Australian climate) during December to April. A neutral IOD has little influence on Australian climate.

Cloudiness near the Date Line has been consistently below average (positive OLR anomalies) since June. Across the Pacific more generally, cloud patterns are typical of La Niña, with below average cloudiness along the equator, and increased cloudiness across the Maritime Continent.

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 November 2021) shows cool anomalies across the sub-surface of the central to eastern equatorial Pacific, which have strengthened and shifted eastward over the past three months. For November, waters were more than two and a half degrees cooler than average across a large region east of 125°W, and reach up to four degrees cooler than average in some areas. Weaker cool anomalies extend to 160°W.

Weak warm anomalies continue across parts of the column depth in the far west of the equatorial Pacific.

For the five days ending 5 December 2021, sub-surface temperatures were close to average across most of the equatorial Pacific. There were small areas of weak warm and weak cool anomalies in the sub-surface of the western and eastern equatorial Pacific, respectively. Due to the sparsity of observations in parts of the equatorial Pacific (point observations are indicated by Xs on the sub-surface temperature plot), confidence in the current state of the sub-surface is lower than it otherwise would be.

La Niña is firmly established in the tropical Pacific. Climate models suggest this La Niña will persist until the late southern hemisphere summer or early autumn 2022. La Niña events increase the chance of above average rainfall across much of northern and eastern Australia during summer.

Most El Niño–Southern Oscillation (ENSO) indicators show clear La Niña patterns. Sea surface temperatures in the tropical Pacific have cooled to La Niña thresholds, with climate model outlooks expecting them to cool further. In the atmosphere, cloud and wind patterns are typical of La Niña, indicating the atmosphere is responding to the changes in ocean temperatures. This feedback process is known as "coupling", and it means La Niña conditions are now expected to be locked in until at least the end of summer.

The negative Indian Ocean Dipole (IOD) is near its end, with IOD index values in the neutral range. However, some signs of the negative IOD persist with increased cloud over the eastern Indian Ocean and strengthened westerly winds. Climate models predict the IOD will remain neutral for the coming months, consistent with its typical seasonal cycle.

The Madden–Julian Oscillation (MJO) has recently entered the western Pacific and strengthened. The MJO is forecast to progress eastwards across the western Pacific over the coming fortnight, which increases the likelihood of above average cloudiness and rainfall across northern Australia and the western Pacific. It also increases the chance that the monsoon will develop in the Australian region in the next week or two—a little earlier than normal.

The Southern Annular Mode (SAM) continues to be positive and is forecast to remain positive levels to at least to the end of the year. A positive SAM during summer typically brings wetter weather to eastern parts of Australia, but drier than average conditions for western Tasmania.

Climate change continues to influence Australian and global climate. Australia's climate has warmed by around 1.44 °C for the 1910–2019 period. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990s. In recent decades there has 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 strongly positive. SAM is expected to weaken, but remain generally positive until the end of the year.

A positive SAM at this time of the year typically brings above average rainfall to eastern parts of Australia, but typically has a drying influence on south-westerly exposed coasts such as western Tasmania.

As we move into summer, the influence of positive SAM towards above average rainfall increases over mainland south-eastern Australia, while the tendency to reduced rainfall decreases for western Tasmania, and there is an increased chance of above average rainfall in eastern Tasmania.

La Niña is active in the tropical Pacific Ocean.

All seven of the international climate models surveyed by the Bureau anticipate further cooling of tropical Pacific sea surface temperatures. All models surveyed indicate La Niña thresholds are likely to be met during December and January. Three models continue the event into February, but by March only one model continues to meet the threshold.

In general, the models anticipate that this La Niña will be short-lived, and of weak to moderate strength though there is some variation in predicted peak strength between the various models. It should be noted that the strength of an event doesn't necessarily equal the strength of its effect. For 2021–22 to be considered a La Niña year, the event will have to be sustained for at least three months.

Regardless of whether La Niña thresholds are sustained for three months or for a shorter period, the presence of La Niña-like patterns in the Pacific increases the chances of above-average rainfall for northern and eastern Australia during spring and the coming summer.