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

The SST map for March shows patchy below average SSTs extending along parts of the equator in the central to eastern Pacific Ocean, extending into the tropics north of the equator in the east of the basin. The strength of these anomalies decreased in March; the breakdown of SST anomalies during autumn is typical of the life cycle of ENSO events.

SSTs were warmer than average in waters around the west of Australia and parts of the north of the Maritime Continent.

March values of the three key NINO indices were: NINO3 −0.3 °C, NINO3.4 −0.4 °C, and NINO4 −0.3 °C.

The sea surface temperature (SST) map for the tropical Pacific Ocean for the week ending 11 April shows patchy cool anomalies remain along parts of the equator in the eastern Pacific. The three NINO indices remain within the ENSO-neutral range.

Warm anomalies persist in part of the far western equatorial Pacific, and have strengthened over the past two weeks. Warm anomalies are present in parts of the north of the Maritime Continent and around much of Australia. Warm anomalies are also present in some areas along the South American coastline.

The latest values of the three NINO indices in the tropical Pacific for the week ending 11 April were: NINO3 −0.3 °C, NINO3.4 −0.3 °C, NINO4 −0.1 °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 11 April was +2.0. The 90-day SOI value was +7.5. The 30-day value has remained within ENSO-neutral thresholds over the past four 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 11 April were close to average across the tropical Pacific.

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 been the strongest climate driver influencing Australia during the last fortnight. The MJO is currently at moderate strength, having moved out of the Australian region and into the western Pacific. As it moves across the western Pacific, the MJO typically acts to suppress rainfall over northern Australia at this time of the year.

Sea surface temperatures (SSTs) in the Indian Ocean are warmer than average across most of the southern half of the basin, and some parts of the north. While warm anomalies have decreased across the north of the basin over the past fortnight, warm SST anomalies persist in some areas to the west and northwest of Western Australia, and may be influencing local weather patterns.

The Indian Ocean Dipole (IOD) is neutral. The latest weekly value of the IOD index to 11 April was +0.12 °C.

IOD outlooks from the five surveyed climate models are currently mixed. Model accuracy is generally lower at this time of year than at other times, so the current outlooks should be viewed with caution. The Bureau will continue to monitor model outlooks as the season proceeds and model skill improves.

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 recently spiked into above average values during the past fortnight. The current positive cloudiness anomaly is the highest value observed in more than a year, following generally below average cloudiness between early to mid-March 2020 and early April 2021.

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 March) shows cooler than average water extending across the top 100 to 150 m of the sub-surface of the central and eastern equatorial Pacific. 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 the Date Line. These warm anomalies remain similar in strength compared to last month, but extended a little farther eastward during March.

For the five days ending 11 April, 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 western equatorial Pacific, reaching more than two degrees above average in a small region. Compared to two weeks ago, these warm anomalies have continued to decrease.

The El Niño–Southern Oscillation (ENSO) is neutral, and with no sign of El Niño or La Niña developing, the Bureau's ENSO Outlook is INACTIVE. Climate model outlooks suggest the tropical Pacific Ocean will remain at neutral ENSO levels at least until September.

Tropical Pacific Ocean sea surface temperatures continue at ENSO-neutral values. Below the surface, much of the central to eastern tropical Pacific has warmed over the past few months, and is now at near-average temperatures. Atmospheric indicators are also at neutral ENSO levels. The Southern Oscillation Index (SOI) is close to zero, while trade winds are mostly near average. Cloudiness near the Date Line has increased in the past week to above-average levels, in contrast to almost all of the preceding 12 months when below-average cloudiness was a feature across the region. The return to ENSO-neutral conditions in autumn is typical of the life cycle of ENSO events.

The Madden–Julian Oscillation (MJO) has been the strongest climate driver influencing Australia during the last fortnight with above average falls in the far northern tropics. The MJO has moved out of the Australian region and into the western Pacific at moderate strength. As it moves across the western Pacific, the MJO typically acts to suppress rainfall over northern Australia at this time of the year.

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

The Indian Ocean Dipole (IOD) is also neutral. It 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 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 El Niño–Southern Oscillation (ENSO) is currently neutral. All of the international climate models surveyed by the Bureau anticipate NINO3.4 will remain neutral throughout the outlook period, with neutral ENSO extending until at least September.