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 28 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. The three NINO indices remain within the ENSO-neutral range.

Warm anomalies which recently emerged in part of the far western equatorial Pacific have strengthened over the past two weeks, including across the Maritime Continent and around much of Australia. Warm anomalies are also present in parts of the far east of the Pacific basin, including along some areas of the South American coastline in the tropics.

The latest values of the three NINO indices in the tropical Pacific for the week ending 28 March were: NINO3 −0.3 °C, NINO3.4 −0.4 °C, NINO4 −0.3 °C.

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 March was +0.5. The 90-day SOI value was +10.9. The 30-day value has remained within ENSO-neutral values over the past two weeks.

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 March were stronger than average over much of the tropical Pacific around and west of the Date Line, and near average strength in the centre and east. Trade wind strength has increased compared to two weeks ago, likely related to the Madden–Julian Oscillation moving into the Australian region.

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 moved into the Australian region at moderate strength and is expected to bring increased cloudiness and rainfall to far northern Australia and the broader Maritime Continent over the next week or two. This also brings an increased risk of tropical low/cyclone activity.

Sea surface temperatures (SSTs) in the Indian Ocean are warmer than average across nearly all 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 28 March was +0.22 °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. July values reach the negative threshold in 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 25 March) shows cooler than average water extending across the top 100 to 150 m of the sub-surface of the equatorial Pacific east of the Date Line. The strength and spatial extent of cooler than average water has decreased compared to February, in line with the break-down of the 2020–21 La Niña.

Warm anomalies persist across large parts of the column depth west of 160°W, with stronger anomalies west of the Date Line. These warm anomalies remain similar in strength compared to last month, but have extended farther eastward during March to date.

For the five days ending 28 March, sub-surface temperatures were close to average across most of the equatorial Pacific.

Weak warm anomalies persist between around 100 and 200 m depth in the central to western equatorial Pacific, reaching more than two degrees above average in the far west.

Areas of both cool and warm anomalies have decreased compared to two weeks ago.

The Bureau's ENSO Outlook has moved from LA NIÑA to INACTIVE as most El Niño–Southern Oscillation (ENSO) indicators have now returned to neutral levels. Climate model outlooks suggest the Pacific will remain at neutral ENSO levels at least until the winter.

Tropical Pacific Ocean sea surface temperatures have persisted at ENSO-neutral values for several weeks. Below the surface, much of the tropical Pacific is now at near average temperatures. Atmospheric indicators are also generally at neutral ENSO levels. The Southern Oscillation Index (SOI) is close to zero, while trade winds are currently being enhanced by the Madden–Julian Oscillation (MJO). Only cloudiness near the Date Line continues to show a weak La Niña-like signature.

These changes are consistent with climate model outlooks, which have indicated a return to ENSO neutral during the southern hemisphere autumn, with little indication of a return to La Niña patterns in the coming months. A return to ENSO neutral conditions in autumn is also typical of the life cycle of ENSO events. All models indicate ENSO will remain neutral until at least the end of the southern winter.

The Madden–Julian Oscillation (MJO) is currently the strongest climate driver influencing Australia. The MJO has moved into the Australian region at moderate strength and is expected to bring increased cloudiness and rainfall to far northern Australia and the broader Maritime Continent over the next week or two. This also brings an increased risk of tropical low/cyclone activity.

The Southern Annular Mode (SAM) is currently neutral and expected to remain neutral for the coming fortnight. A neutral SAM has little influence on Australian rainfall.

The Indian Ocean Dipole (IOD) is also 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 Annular Mode (SAM) is currently neutral and expected to remain neutral for the coming fortnight. A neutral SAM has little influence on Australian rainfall.

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

The 2020–21 La Niña has concluded. All of the international climate models surveyed by the Bureau anticipate NINO3.4 will remain neutral until at least the end of winter. The spread of the individual model outlooks shows neutral ENSO is by far the most likely scenario, with only a very small proportion of model runs indicating a return to La Niña conditions is possible later in 2021, and El Niño is very unlikely.