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 19 December 2021 were cooler than average along the equator across most of the Pacific Ocean. Weak warm SST anomalies continue over parts of the Maritime Continent, with stronger warm anomalies around northern Australia. Both warm and cool anomalies remain similar to two weeks ago, and show a well-developed La Niña pattern.

The latest values of the three NINO indices for the week ending 19 December 2021 were: NINO3 −0.8 °C, NINO3.4 −0.7 °C, and NINO4 −0.5 °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 19 December 2021 were stronger than average across most of the western half of the tropical Pacific, and close to average in the eastern tropical 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) is in the western Pacific Ocean. The MJO is expected to remain there until early January. MJO activity in the western Pacific increases the likelihood of above average cloudiness and rainfall across northern Australia and may assist the development of the Australian monsoon by encouraging westerly winds over the area. As these westerly winds get further into the western Pacific, they could act to temporarily weaken the La Niña.

The latest weekly value of the Indian Ocean Dipole (IOD) index to 19 December 2021 was −0.31 °C, within neutral bounds.

IOD index values have been within the neutral range for around a month, and the residual atmospheric pattern has now also returned to patterns consistent with neutral IOD.

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, cloudiness remains increased across the Maritime Continent, and decreased along the equator across much of the western and central Pacific.

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 19 December 2021, sub-surface temperatures were close to average across most of the equatorial Pacific. There were areas of cool anomalies in the sub-surface of the eastern equatorial Pacific and warm anomalies in the western equatorial Pacific; both areas reach more than three degrees cooler/warmer than average 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 conditions continue 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 indicators of the El Niño–Southern Oscillation (ENSO) show clear La Niña patterns. Sea surface temperatures (SSTs) in the tropical Pacific remain at, or exceeding, La Niña thresholds, with cooler water beneath the surface to support further cooling. In the atmosphere, cloud, wind, and pressure patterns are typical of La Niña, indicating the atmosphere is responding to the ocean changes below. These atmospheric changes also reinforce the changes observed in the ocean. This feedback process is known as "coupling" and allows La Niña conditions to be sustained for an extended period.

The Indian Ocean Dipole (IOD) is neutral. Cloud and wind patterns, as well as SSTs, have now eased back from a negative IOD-like state and become more clearly neutral. Climate models predict the IOD will remain neutral for the coming months, consistent with its typical seasonal cycle. A neutral IOD has little influence on Australian climate.

The Madden–Julian Oscillation (MJO) remains in the western Pacific. The MJO is forecast to progress eastwards across the western Pacific over the coming fortnight, which would typically increase cloudiness and rainfall across northern Australia and the western Pacific. It also increases the chances that the monsoon will develop in the Australian region by encouraging westerly winds over the area. However, as these westerly winds get further into the western Pacific, they could act to temporarily weaken the La Niña.

The Southern Annular Mode (SAM) continues to be positive. It is forecast to remain at positive levels until the end of the year before returning to neutral. 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 positive. SAM is expected to remain positive until the end of the year.

A positive SAM during summer typically brings above average rainfall to eastern parts of Australia, including eastern Tasmania, but typically has a drying influence on south-westerly exposed coasts such as western 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 January, four remain above threshold in February and another two are borderline, but by March only one model continues to meet the threshold.

For 2021–22 to be considered a La Niña year, the event needs to be sustained for at least three months in total.

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 this summer. It should be noted that the strength of an event doesn't necessarily equal the strength of its effect.