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

In the tropical Pacific Ocean, October sea surface temperatures (SSTs) were:

• up to 1.2 °C warmer than average in the far western tropical and far eastern equatorial Pacific Ocean
• up to 1.2 °C cooler than average in the central and eastern equatorial Pacific, east of 170°W

In Australian coastal waters, October SSTs were:

• up to 2 °C warmer than average in waters surrounding most of Australia, reaching up to 3 °C warmer than average off the north-west and south-east coasts.

Around the Maritime Continent, October SSTs were:

• up to 2 °C warmer than average

The Bureau's long-range forecast for December 2024 to February 2025 indicates SSTs are likely to be:

• up to 1.2 °C warmer than average in the far western Pacific (west of 170°E)
• close to average across most of the equatorial Pacific, east of 170°E with the exception of a small region of the equatorial Pacific between 120°E and 130°E, where it is forecast to be up to 0.8 °C cooler than average
• up to 1.2 °C warmer than average across most of Australia's coastal waters, and reaching up to 2 °C warmer in the north-west and up to 3 °C warmer in the south-east
• up to 1.2 °C warmer than average across the Maritime Continent.

ENSO and the IOD are only broad indicators of the expected climate. The long-range forecast provides better guidance on local rainfall and temperature patterns.

For the week ending 24 November, sea surface temperatures (SSTs) were:

• 0.4–2 °C warmer than the 1991–2020 average in the far western equatorial Pacific and parts of the central and eastern Pacific north of the equator
• 0.8–2 °C cooler than average in the central and eastern equatorial Pacific, east of the Date Line
• warmer than average across much of the north Pacific, with much of the region surrounding and to the east of Japan more than 3–4 °C warmer than average
• 0.4–2 °C warmer than average around most of Australia's coastline and parts of the Tasman and Coral seas, with areas off the south-east and north-west coasts up to 3 °C warmer than average
• 0.4–2 °C warmer than average across most of the Maritime Continent.

The Niño indices for the week ending 24 November were: Niño3, −0.05 °C; Niño3.4, −0.14 °C; and Niño4, +0.09 °C, having warmed in recent weeks. The Niño3.4 index reflects historically neutral ENSO conditions.

• The SOI values reflect ENSO-neutral conditions.
• The 30–, 60– and 90-day Southern Oscillation Index (SOI) for the period ending 24 November were +5.1, +4.7 and +3.4, respectively.
• Sustained positive values of the SOI above +7 typically indicate La Niña while sustained negative values below −7 typically indicate El Niño. Values between +7 and −7 generally indicate neutral conditions.

• Trade winds for the 5 days ending 24 November were stronger than average in the western Pacific and close to average across the central Pacific.
• There is a lack of data observations in the eastern Pacific, which makes it difficult to identify trade wind anomaly patterns in this region.
• Westerly wind anomalies in the central and eastern tropical Pacific during late October and early November have likely slowed further cooling towards La Niña thresholds in recent weeks.
• During La Niña events, there is typically a sustained strengthening of trade winds across much of the tropical Pacific, while during El Niño there is a sustained weakening, or even reversal, of trade winds.

• A moderate to strong Madden–Julian Oscillation (MJO) pulse is currently located in the Indian Ocean (as at 24 November).
• Most models indicate the MJO will shift eastwards over the coming fortnight and weaken in early December as it moves across the Maritime Continent.

Current state

• The Indian Ocean Dipole (IOD) index for the week ending 24 November was −0.54 °C, having been below the negative IOD threshold (–0.4 °C) since mid-October.
• To be classified as a negative IOD event, the IOD index needs to be at values below the negative IOD threshold (–0.4 °C) for at least 8 weeks.
• Sea surface temperatures (SSTs) for the week ending 24 November were 0.8–2 °C warmer than the 1991–2020 average across much of the central and eastern Indian Ocean and 0.4–1.2 °C warmer than average in the western equatorial Indian Ocean, meaning the western Indian Ocean is cooler than the eastern Indian Ocean. This ocean pattern is typical of a negative IOD phase.
• SSTs were 1.2–3 °C warmer than average for waters surrounding north-west Australia.

Forecast

• All but one of the surveyed climate models indicate that the IOD index will return to neutral levels in December.
• IOD forecast skill has historically been moderate for forecasts out to 1 month ahead.

• Cloudiness near the equatorial International Date Line is currently below average as at 24 November.
• Cloudiness has been below average since early September.
• Prior to September, cloudiness fluctuated around average for most of the year.
• Equatorial cloudiness near the International Date Line typically increases during El Niño (below average outgoing longwave radiation - OLR) and decreases during La Niña (above average OLR).

The equatorial Pacific sub-surface temperature anomalies for the 26 days ending 19 November 2024 show:

• cooler than average waters in the eastern half of the equatorial Pacific down to about 175 m depth; cooler waters peak around 25 to 100 m depth in the eastern Pacific where they are more than 3 °C cooler than average
• warmer than average waters in the western half of the equatorial Pacific down to about 300 m depth in the far western Pacific. Waters are 2 to 4 °C warmer than average in the far western Pacific between 75 m and 150 m depth
• generally only small changes over recent weeks with some weak warming across the basin.

For the 5 days ending 24 November 2024, the analysis shows:

• sub-surface temperatures up to 2 °C cooler than average in areas of the central equatorial Pacific (between 125 m and 150 m depth) and eastern equatorial Pacific (between 50 m to 100 m depth).
• waters are more than 2 °C warmer than average in the top 25 m of the far eastern Pacific.
• sub-surface temperatures are within 2 °C warmer or cooler than average elsewhere.

The El Niño–Southern Oscillation (ENSO) remains neutral, with sea surface temperatures (SSTs) in the central equatorial Pacific Ocean at ENSO-neutral levels. Atmospheric indices, such as those related to patterns of surface pressure, cloud and trade winds, are broadly consistent with an ENSO-neutral state. While some have displayed La Niña-like signals over recent months, a consistent and sustained shift in the atmosphere has not been observed. Ocean temperatures in the central equatorial Pacific have started to warm in recent weeks, away from the La Niña threshold, although they are still cooler than the historical average.

The Bureau's model suggests SSTs are likely to remain within the ENSO-neutral thresholds (−0.8 °C to +0.8 °C) throughout the forecast period to February 2025. Of the 6 other climate models surveyed, 2 models suggest SSTs in the tropical Pacific are likely to exceed the La Niña threshold (below −0.8 °C) throughout December to February, which is sufficient time to be classified as a La Niña event, though this would be considered a very short-lived event compared to the historical record. All models forecast neutral ENSO values by March.

The Indian Ocean Dipole (IOD) index has been below the negative IOD threshold (−0.40 °C) since mid-October. If the IOD index remains below the threshold for another week, it would indicate a negative IOD event is underway. However, all but one of the surveyed climate models indicate that the IOD index is expected to return to neutral levels in December, in line with the typical IOD event lifecycle.

Global SSTs remain at near record levels as at 24 November, with temperatures since July falling just short of the record temperatures observed during 2023, yet above all other years since observations began in 1854. The sustained nature of this significant global ocean heat suggests that climate indicators such as ENSO and IOD may not behave or evolve as they have in the past.

The Southern Annular Mode (SAM) index is neutral as at 23 November, having been positive for most of November. It is forecast to become positive again in the coming fortnight. SAM is also forecast to have a greater than usual chance of being in the positive phase during December.

A moderate to strong pulse of the Madden–Julian Oscillation (MJO) is currently located in the Indian Ocean (as at 24 November). Most models indicate the MJO will shift eastwards over the coming fortnight and weaken in early December as it moves across the Maritime Continent.

ENSO, IOD, MJO and SAM are broad indicators of the expected climate and are just some of many factors in a complex system. The long-range forecast provides better guidance on local rainfall and temperature patterns.

• The Southern Annular Mode (SAM) is neutral as at 23 November, having been positive for most of November.
• The SAM index is forecast to become positive in the coming fortnight.
• Predictability of the SAM beyond two weeks is typically low but at this time of the year, there is some predictability up to 2 months ahead.
• SAM is forecast to have a greater than usual chance of being in the positive phase during December.

• The Bureau's model suggests SSTs are likely to remain within the ENSO-neutral range (−0.8 °C to +0.8 °C) throughout the forecast period.
• Of the 6 climate models surveyed (in addition to the Bureau model), 4 also suggest SSTs are likely to remain within the ENSO-neutral range. The remaining 2 suggest SSTs in the tropical Pacific are likely to meet or exceed the La Niña threshold (below −0.8 °C) throughout December to February, which would be a sufficient length of time to be classified as a La Niña event.
• Should a La Niña develop, it is forecast to be relatively weak (in terms of the magnitude of the SST anomaly) and short-lived, with all models forecasting ENSO-neutral by March 2025.
• In order to be considered to be in a La Niña event, changes in both the ocean and atmosphere need to be observed, to see a coupling between the Pacific Ocean and atmosphere. This coupling is a characteristic of a La Niña event and is what strengthens and sustains an event for an extended period.
• At this time of year, ENSO forecast skill is high for up to 4 months ahead.