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

The SST map for January shows below average SSTs extending along the equator in the western and central tropical Pacific Ocean, extending into the tropics south of the equator in the east of the basin. The strength of these anomalies has decreased in eastern parts of the basin compared to December but has increased in the western half of the basin.

SSTs were warmer than average in much of the area around Australia, particularly in the northwest and southeast.

January values of the three key NINO indices were: NINO3 −0.4 °C, NINO3.4 −0.8 °C, and NINO4 −0.9 °C.

The sea surface temperature (SST) map for the tropical Pacific Ocean for the week ending 28 February shows cool anomalies extending along the equator through much of the Pacific, and also in parts of the eastern Pacific south of the equator. Warm anomalies remain across parts of the Maritime Continent and in the waters close to parts of Australia, particularly the northern Coral Sea and to the east and south of Tasmania.

The latest values of the three NINO indices in the tropical Pacific for the week ending 28 February were: NINO3 −0.4 °C, NINO3.4 −0.8 °C, NINO4 −0.7 °C. NINO3.4 has cooled slightly compared to two weeks ago, although recent weeks have seen the region warm. Both NINO3 and NINO4 have warmed over the past two weeks.

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 28 February was +11.0. The 90-day SOI value was +15.3. Recent 30-day values have continued their gradual decline from a peak of around +20 maintained for much of early to mid-January, but continue to remain within La Niña thresholds.

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 28 February were stronger than average over much of the western half of the tropical Pacific, and near average strength in the centre and east. Trade wind strength has increased 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 currently weak.

The MJO is expected to move across the tropical Americas and into the Atlantic Ocean by mid-March; typically this scenario is associated with below average cloudiness and rainfall across northern Australia and the Maritime Continent.

Sea surface temperatures (SSTs) in the Indian Ocean are warmer than average across much of the mid-latitudes in the southern half of the basin, and parts of the north of the basin between Indonesia and the east of the Arabian Sea. Warm SST anomalies to the northwest of Western Australia may be influencing local weather patterns.

The Indian Ocean Dipole (IOD) is neutral. The latest weekly value of the IOD index to 28 February was −0.15 °C.

All but one of the five surveyed climate models expect the IOD to remain neutral through autumn. IOD events are typically unable to form between December and April. This is because the monsoon trough shifts south over the tropical Indian Ocean and alters wind patterns, preventing the IOD pattern from being able to form.

Cloudiness near the Date Line has generally been below average since early to mid-March 2020. While still below average, the tendency for reduced cloudiness was lower during February than in the previous three months.

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 (to 25 February) shows cooler than average water extending across the top 200 m of the sub-surface of the equatorial Pacific east of around 160°E. The strength and spatial extent of cooler than average water has remained similarly strong in February and January, with the overall pattern fairly consistent since September.

Warm anomalies persist across large parts of the column depth west of the Date Line, with warm anomalies underlying the shallower cool anomalies between the Date Line and 160°E. These warm anomalies have strengthened month-on-month since October.

For the five days ending 28 February, sub-surface temperatures were above average between around 100 and 250 m depth west of the Date Line, reaching more than four degrees above average around 150°E and 150 m depth; this is a strengthening of warm anomalies compared to two weeks ago.

In the eastern half of the equatorial Pacific, cool anomalies persist across the top 150 m, reaching three degrees cooler than average across a region around 130°W and 50 to 100 m depth. These cool anomalies have weakened compared to two weeks ago.

The 2020–21 La Niña has passed its peak and is now weakening. Climate model outlooks indicate the El Niño–Southern Oscillation (ENSO) will return to neutral (neither La Niña nor El Niño) during autumn.

While La Niña's influence on Australian rainfall typically wanes during autumn when events usually decay, it can still bring above average rainfall to parts of northern and eastern Australia during the final months of the northern wet season.

Tropical Pacific Ocean sea surface temperatures are currently close to La Niña threshold. However, atmospheric indicators such as the Southern Oscillation Index (SOI), cloudiness near the Date Line, and trade winds clearly remain at La Niña levels. Waters beneath the surface remain cooler than average, but the strength of cool anomalies has begun to ease.

The Madden–Julian Oscillation (MJO) is currently weak. It is forecast to move into the tropical Americas and Africa in the coming week. When the MJO is over the Americas at this time of the year, tropical areas across northern Australia and the Maritime Continent typically experience less cloud and rainfall than usual.

After persisting at positive values for the first half of February, the Southern Annular Mode (SAM) returned to neutral levels. Forecasts indicate neutral SAM values will persist for the coming fortnight. A neutral SAM has little influence on Australian rainfall.

The Indian Ocean Dipole (IOD) is currently neutral. The IOD typically has little influence on Australian climate from December to April.

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) has recently been positive but is expected to be neutral throughout March.

During autumn SAM has less influence on rainfall than during other times of the year.

The 2020–21 La Niña has passed its peak, with all of the international climate models surveyed by the Bureau anticipating NINO3.4 will continue to decline, becoming neutral by mid-autumn. Typical La Niña influences on Australian climate are likely to be felt during early autumn, even as La Niña decays.

La Niña increases the likelihood of above-average rainfall across much of northern and eastern Australia during summer and early autumn. 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.