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

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

• up to 1.2 °C warmer than average across much of the western tropical Pacific Ocean, and reaching up to 3 °C warmer than average in the far east
• up to 2 °C cooler than average in patches of the equatorial Pacific, east of 130°W.

In Australian coastal waters, August SSTs were:

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

Around the Maritime Continent, August SSTs were:

• up to 2 °C warmer than average to the north of the Maritime Continent, nearer to average for southern parts.

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

• between 0.8 to 2 °C warmer than average in northern and eastern Australian coastal waters
• up to 1.2 °C warmer than average in southern and western Australian coastal waters
• up to 2 °C warmer than average across parts of the Tasman Sea
• up to 2 °C cooler than average in the central equatorial Pacific, between 160°W and 100°W; and up to 1.2 °C warmer than average for most of the tropical Pacific west of 170°W and south-west Pacific.

Phenomena such as 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 29 September 2024, sea surface temperatures (SSTs) were:

• 0.8–2 °C warmer than the 1991–2020 average in the far western equatorial Pacific
• 0.8–2 °C cooler than average in the central equatorial Pacific
• mostly 0.4–0.8 °C warmer than average in the far eastern Pacific
• warmer than average across much of the north Pacific, with much of the region surrounding and to the east of Japan more than 2–4 °C warmer than average
• 0.8–2 °C warmer than average around much of Australia's coastline and across most of the Maritime Continent, with much of the area between north-west Australia and Indonesia 1.2–2 °C warmer than average.

The Niño indices for the week ending 29 September 2024 are: Niño3, −0.17 °C; Niño3.4, −0.43 °C; and Niño4, +0.13 °C. The Niño3.4 index has cooled in recent weeks, however its values reflect historically neutral ENSO conditions.

• The 30–, 60– and 90-day Southern Oscillation Index (SOI) for the period ending 29 September were +0.4, +3.0 and −0.4 respectively.
• The SOI values reflect ENSO-neutral conditions.
• 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 wind strength for the 5 days ending 28 September was close to average across the tropical Pacific.
• Monthly averaged trade winds have been stronger than average across the equatorial Pacific since July.
• 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 weak to moderate pulse of the Madden–Julian Oscillation (MJO) is currently in the Western Hemisphere and Africa (as of 29 September).
• Most models suggest the MJO pulse will move eastwards towards the Indian Ocean and weaken in the coming days. Some models suggest the MJO may re-emerge in mid-October over the Maritime Continent region.

Current state

• The Indian Ocean Dipole (IOD) is neutral. The IOD index for the week ending 29 September was −0.39 °C.
• Sea surface temperatures (SSTs) for the week ending 29 September 2024 were 0.8–2 °C warmer than the 1991–2020 average across much of the central and eastern Indian Ocean but close to average in parts of the western Indian Ocean.
• Some cooler than average waters have expanded near the Horn of Africa in the last fortnight over the western pole of the IOD.
• Closer to Australia, SSTs were up to 2 °C warmer than average for waters surrounding northern WA.

Forecast

• Most climate models indicate the IOD is likely to remain neutral, but weakly negative, for the rest of the year.
• One model indicates a negative IOD during October and November.
• IOD forecast skill has historically been low at this time of year for forecasts beyond two months ahead.

• Cloudiness near the equatorial International Date Line is currently below average as of 28 September.
• Cloudiness has been below average for most of September.
• Prior to September, cloudiness has fluctuated around average levels for most of the year.
• Equatorial cloudiness near the International Date Line typically increases during El Niño (below average OLR) and decreases during La Niña (above average OLR).

The equatorial Pacific sub-surface temperature anomalies for the 30 days ending 25 September 2024 show:

• cooler than average waters in the eastern half of the equatorial Pacific down to about 200 m depth; waters are more than 4 °C cooler than average in a small area around 100 to 150 m depth
• warmer than average waters in the western half of the equatorial Pacific down to about 200 m depth, increasing to 300 m depth in the far west. Waters are 2 to 3 °C warmer than average in a couple of small pockets around 125 m depth.

For the 5 days ending 28 September 2024:

• the equatorial Pacific sub-surface temperature anomalies are within 2 °C of average for all areas, except in the shallow eastern sub-surface, where waters are more than 2 °C warmer than average.
• there are reduced observations in the eastern Pacific sub-surface in the latest 5-day analysis.

The El Niño–Southern Oscillation (ENSO) is neutral, with both sea surface temperatures (SSTs) in the central equatorial Pacific Ocean and atmospheric patterns at ENSO-neutral levels. While some atmospheric indicators such as pressure, cloud and trade wind patterns over the Pacific have been more La Niña-like over the past few weeks, there has yet to be a consistent/sustained signal.

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 to February 2025.

Of the 6 other climate models surveyed, 3 suggest SSTs in the tropical Pacific are likely to exceed the La Niña threshold (below −0.8 °C) from October, and another 3 models forecast SSTs to fall just short of the threshold from November. Should a La Niña develop in the coming months, it is forecast to be relatively weak (in terms of the strength of the SST anomaly) and short-lived, with all models indicating a return to neutral by February.

The Indian Ocean Dipole (IOD) is currently neutral, with the weekly IOD index of −0.39 °C (as of 29 September). Most models indicate that the IOD is likely to remain neutral, but weakly negative, for the rest of the year. An IOD event is unlikely.

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

The Southern Annular Mode (SAM) is negative (as at 28 September). The SAM index is forecast to return to neutral levels during the coming week. A negative SAM typically decreases rainfall in eastern Australia during spring.

The Madden–Julian Oscillation (MJO) is currently located in the Western Hemisphere (as at 29 September). Most models suggest the MJO will move eastwards towards the Indian Ocean and weaken in the coming days and may reemerge in the Maritime Continent in mid-October.

ENSO, the IOD, the MJO and the 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 negative (as of 28 September) and has been hovering around the negative threshold for the past week and a half.
• The SAM index is forecast to return to neutral levels during the coming week.
• A negative SAM typically decreases rainfall in eastern Australia during spring.
• Predictability of the SAM beyond two weeks is typically low.

• ENSO is currently neutral.
• 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 other climate models surveyed, 3 suggest SSTs in the tropical Pacific are likely to exceed the La Niña threshold (below −0.8 °C) from October, while the other 3 models forecast SSTs to fall just short of the threshold.
• Should a La Niña develop in the coming months, it is forecast to be relatively weak (in terms of the magnitude of the SST anomaly) and short-lived, with all models indicating a return to neutral by February 2025.
• ENSO forecast skill is high at this time of year for up to 4 months ahead.