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.

Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 25 April were close to average across most of the equatorial Pacific Ocean. Some cool anomalies persist along part of the South American coastline in the tropics.

Warm anomalies persist in part of the far western equatorial Pacific, parts of the Maritime Continent, and around much of Australia—particularly around the west and south-west coast.

All three NINO indices are within the ENSO-neutral range. The latest values of the three NINO indices in the tropical Pacific for the week ending 25 April were: NINO3 −0.2 °C, NINO3.4 −0.3 °C, and NINO4 at 0.0 °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 25 April was +0.5. The 90-day SOI value was +6.0. Both are within ENSO-neutral 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 25 April were close to average across the tropical Pacific, consistent with a neutral ENSO state.

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 over tropical America. It is expected to move eastwards towards Africa in the coming fortnight at moderate to strong intensity. At this time of the year, the MJO influence is transitioning to the northern hemisphere, and therefore is beginning to have a smaller influence on northern Australia, This influence typically would suppress rainfall across far northern Australia, as well as the broader Maritime Continent.

The Indian Ocean Dipole (IOD) is neutral. The latest weekly value of the IOD index to 25 April was +0.32 °C.

Weekly 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. Warm anomalies to the west and north-west of Western Australia generally remain similar to two weeks ago, and may be influencing local weather patterns. Warm anomalies have generally increased in strength in the north of the basin over the past fortnight.

IOD outlooks from the five surveyed climate models are currently mixed. Most climate models currently indicate the IOD is likely to remain neutral at least through early winter. 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 generally been close to average during April.

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 22 April) shows weak cool anomalies remain across the top 50 to 100 m of the central and eastern equatorial Pacific. The strength of these cool anomalies has decreased significantly compared to March, in line with the return to a neutral ENSO state.

Warm anomalies persist across parts of the column depth west of the Date Line. These warm anomalies have decreased in strength and spatial extent compared to March.

For the five days ending 25 April, sub-surface temperatures were close to average across most of the equatorial Pacific.

Warm anomalies persist in a small region between around 100 and 200 m depth in the western equatorial Pacific, reaching more than three degrees above average near the western edge of the basin. These warm anomalies are stronger than they were two weeks ago. On the whole, the sub-surface is consistent with an ENSO neutral state. 

The El Niño–Southern Oscillation (ENSO) remains neutral. Climate model outlooks indicate this neutral phase will last at least until September. With little sign of El Niño or La Niña developing, the Bureau's ENSO Outlook status is INACTIVE.

Oceanic indicators of ENSO persist at neutral levels, with Pacific sea surface temperatures close to average across most of the equatorial region. Beneath the surface, temperatures are also near-average. The Southern Oscillation Index (SOI), an atmospheric indicator of ENSO, has now seen both the 30-day and 90-day SOI return to neutral levels. Similarly, winds and cloudiness near the Date Line persist at levels consistent with a neutral ENSO state.

After stalling in the Pacific over the past week, the Madden–Julian Oscillation (MJO) is currently over tropical America. It is forecast to move eastwards towards Africa during the coming fortnight. At this time of the year, the MJO influence is shifting to the northern hemisphere, and therefore begins to have less influence on northern Australia. When the MJO is active over the African region, convection is typically suppressed over far northern Australia, as well as the tropical regions to the north of Australia.

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 currently neutral and forecast to remain so at least through early winter.

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 until at least September.