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

The SST map for December shows below average SSTs extending along the equator in the western tropical Pacific Ocean, extending into the tropics south of the equator in the east of the basin. The strength of these anomalies has decreased slightly along the equator in the central and eastern parts of the basin compared to November though their extent has increased to be further west.

The strength of warmer than average SST anomalies in the Tasman Sea has decreased during December but warm anomalies to the northwest of Australia and along parts of the east coast have intensified.

The December values of the three key NINO indices were: NINO3 −0.5 °C, NINO3.4 −0.8 °C, and NINO4 −0.7 °C.

The sea surface temperature (SST) map for the tropical Pacific Ocean for the week ending 17 January shows cool anomalies around the equator extending west of 155°E to south of the equator in the eastern Pacific. Warm anomalies remain around the Maritime Continent and in the waters close to much of northern and southeast Australia.

The latest values of the three NINO indices in the tropical Pacific for the week ending 17 January were: NINO3 −0.5 °C, NINO3.4 −0.9 °C, NINO4 −1.0 °C. NINO3 has warmed slightly while NINO3.4 and NINO4 have cooled compared to two weeks ago.

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

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 17 January was +19.5. The 90-day SOI value was +14.0.

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 17 January were stronger than average over the central and western tropical Pacific. Trade wind strength is stronger compared to two weeks ago.

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 located over the Maritime Continent. It is moderate in strength with some models indicating a weakening in strength and rapid movement into the western Pacific Ocean in the coming week. Along with other tropical wave activity, the MJO is expected to maintain conditions favourable for above-average rainfall and tropical low formation in the Australian region over the coming fortnight.

Sea surface temperatures in the Indian Ocean are warmer than average close to the Australian coast and south of 35 °S. Compared to two weeks ago, these anomalies have strengthened slightly. There is a region of cooler than average temperatures around 30 °S. The Indian Ocean Dipole (IOD) is neutral. The latest weekly value of the IOD index to 17 January was −0.4 °C.

Five of the six surveyed climate models expect the IOD to remain neutral through summer. IOD events are typically unable to form between December and April as the monsoon trough shifts south over the tropical Indian Ocean.

Cloudiness near the Date Line has generally been below average since early to mid-March 2020. During the past fortnight, the anomaly has been more consistent and stronger.

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 shows cooler than average water extending across the top 200 m of the sub-surface of the equatorial Pacific from around the Date Line and eastward across the basin.  The strength and extent of cooler than average water has remained fairly consistent since September with a slight weakening in November.

Warm anomalies persist across large parts of the column depth west of the Date Line, decreasing in depth towards the west of the basin. These warm anomalies have strengthened slightly in December.

For the five days ending 17 January, sub-surface temperatures were above average in the western equatorial Pacific, reaching more than 2 °C above average west of 170° E between a depth of 100–200 m. These warm anomalies cover a smaller volume than they did two weeks ago. In the central and eastern equatorial Pacific, cool anomalies (up to around 2 °C below average) persist at a depth of 50–150 m.

The 2020–21 La Niña is likely to have reached its peak with respect to sea surface temperature patterns in the eastern and central Pacific Ocean. However, impacts associated with La Niña, such as above average rainfall in eastern and northern Australia, are expected to persist into early autumn, with climate outlooks indicating above-average rainfall is likely across much of the country, particularly in eastern Queensland.

Over the past fortnight the sea surface temperatures across the western and central Pacific Ocean have cooled slightly while those in the eastern side of the basin have warmed. The Southern Oscillation Index continues to remain high with a value of +19.5, well above the La Niña threshold of +7. Model outlooks indicate a return to neutral conditions during the late southern summer or early autumn.

The Southern Annular Mode (SAM) has decreased towards neutral values and is expected to be neutral for the next fortnight. A strongly positive SAM over the last month was driven by an exceptionally strong polar vortex over Antarctica which has largely subsided now.

The Madden–Julian Oscillation (MJO) is located over the Maritime Continent and moderate in strength. Some models indicate it will weaken in the coming week before strengthening again in the western Pacific Ocean. Along with other tropical wave activity, the MJO can be expected to maintain above-average rainfall and tropical cyclone activity in the Australian region over the coming fortnight.

Climate change is also influencing the Australian climate. Australia's climate has warmed by 1.44 ± 0.24 °C over the period 1910–2019, while recent decades have seen increased rainfall across northern Australia during the northern wet season (October–April), with more high-intensity, short-duration rainfall events.

The Southern Annual Mode (SAM) is neutral and is expected to remain neutral for the next fortnight. Strongly positive values over the past month were driven by an exceptionally strong Antarctic polar vortex which has largely subsided.

La Niña is likely at its peak with all but one of the international climate models surveyed by the Bureau indicating a return to neutral conditions (neither El Niño nor La Niña) by early southern autumn. However, typical La Niña impacts are likely to be felt, even as the La Niña weakens.

La Niña increases the likelihood of above-average rainfall across much of Australia during spring, and across much of northern and eastern Australia during summer. Below-average daytime temperatures are typically observed for large parts of the country, particularly Queensland. It also increases the chance of tropical cyclones and earlier first rains of the northern wet season, as we saw this season.