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

The SST map for February shows below average SSTs extending along most of the equator in the tropical Pacific Ocean, extending into the tropics south of the equator in the east of the basin and north of the equator in parts of the central Pacific. The strength of these anomalies has decreased across much of the basin compared to January, but was stronger in parts of the eastern equatorial Pacific.

SSTs were slightly warmer than average across much of the waters close to Australia.

February values of the three key NINO indices were: NINO3 −0.4 °C, NINO3.4 −0.7 °C, and NINO4 −0.8 °C.

The sea surface temperature (SST) map for the tropical Pacific Ocean for the week ending 14 March shows patchy cool anomalies remain along parts of the equator in the central to eastern Pacific, as well as in parts of the eastern Pacific north of the equator. Cool anomalies have decreased substantially compared to two weeks ago. Warm anomalis have emerged in part of the far eastern equatorial Pacific, and extend along some areas of the South American coastline in the tropics.

Warm anomalies remain across parts of the Maritime Continent and in the waters close to parts of eastern and much of western Australia, and to the east and south of Tasmania.

The latest values of the three NINO indices in the tropical Pacific for the week ending 14 March were: NINO3 −0.1 °C, NINO3.4 −0.4 °C, NINO4 −0.3 °C. All three NINO indices have warmed compared to two weeks ago and are within the ENSO-neutral range.

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 14 March was +3.6. The 90-day SOI value was +13.1. Both recent 30-day and 90-day values have continued to decline over the past two weeks, with the 30-day value dropping below La Niña thresholds during the past week.

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 12 March were stronger than average over much of the western tropical Pacific, and near average strength in the centre and east. However, trade wind strength has decreased slightly 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) has recently reappeared in the African region at moderate strength, but is forecast to weaken over the coming week. At this time of the year, an MJO pulse near Africa is often associated with below-average rainfall across northern Australia. However, if the MJO weakens as predicted its influence upon Australian rainfall in the coming weeks will be greatly reduced.

Sea surface temperatures (SSTs) in the Indian Ocean are warmer than average across much of the basin. Warm SST anomalies to the west and 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 14 March was +0.05 °C.

All but one of the five surveyed climate models expect the IOD to remain neutral through autumn, with one touching on the negative threshold value during May. Values for July reach the negative threshold for three of the five models, indicating potential for negative IOD to develop. However model accuracy is generally lower at this time of year than at other times, so the current outlooks should be viewed with caution.

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.

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 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 around and 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 12 March, sub-surface temperatures were above average between around 100 and 200 m depth west of the Date Line, reaching more than four degrees above average around 150°E to 160°E and 150 m depth.

In the eastern half of the equatorial Pacific, cool anomalies persist between 50 m and 150 m depth, reaching more than three degrees cooler than average around 135°W and 50 to 100 m depth.

In general, both cool and warm anomalies are similar to two weeks ago.

The 2020–21 La Niña is nearing its end, with most oceanic indicators of the El Niño-Southern Oscillation (ENSO) now at neutral levels. However, a number of atmospheric indicators remain at La Niña levels, meaning La Niña's influence is likely to persist into April, with outlooks indicating a wetter than average month for northern and eastern parts of Australia.

Tropical Pacific Ocean sea surface temperatures have returned to ENSO-neutral values in the past fortnight. Below the surface, waters have also been warming. However, atmospheric indicators such as cloudiness near the Date Line and trade winds persist at La Niña levels. The Southern Oscillation Index (SOI) in recent days has dipped below La Niña thresholds, although this may just be a temporary easing.

These changes in indicators are consistent with climate model outlooks, which for several weeks have indicated a return to ENSO neutral during the southern hemisphere autumn. While around 40% of past La Niña events have re-strengthened for a second year, there are currently no models suggesting that La Niña will return during winter.

The Madden–Julian Oscillation (MJO) has recently reappeared in the African region at moderate strength but is forecast to weaken in the coming week. At this time of the year, an MJO pulse near Africa is often associated with below-average rainfall across northern Australia. However, if the MJO weakens as predicted its influence upon Australian rainfall in the coming weeks will be greatly reduced.

The Southern Annular Mode (SAM) has briefly reached positive levels. However, this is expected to be short-lived, with forecasts indicating 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 continues to influence Australian and global climate. Australia's climate has warmed by 1.44 ± 0.24 °C over 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. Southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades.

The Southern Annual Mode (SAM) briefly reached positive levels in recent days. However, this is expected to be short-lived, with forecasts indicating neutral SAM values will persist for the coming fortnight.

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

The 2020–21 La Niña is nearing its end. All of the international climate models surveyed by the Bureau anticipate NINO3.4 will return to neutral by May. Despite the event continuing to decay, La Niña influences on Australian climate are likely to persist into April.

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.