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

Sea surface temperatures (SSTs) for November 2023 were warmer than average across almost all of the equatorial Pacific Ocean. Across much of the tropical Pacific between 10°S and 10°N, SST anomalies were more than 0.8 °C warmer than the long-term (1961–1990) average, increasing to up to 3 °C warmer than the long-term average east of the Date Line.

The extent of warm anomalies across the equatorial Pacific has slightly decreased compared to October.

Cool anomalies off the west coast of Java, Indonesia have also decreased in magnitude compared to October.

Warm SST anomalies also continued in the western Tasman Sea, including off most of the south-eastern coast of Australia, and have strengthened across other parts of the Tasman Sea. Warm anomalies to the west of Australia decreased in magnitude compared to October, with waters warmer than 0.8 °C above average surrounding much of Western Australia.

The Bureau's long-range forecasts indicate warmer than average SSTs (up to around 2 °C warmer than average) off the coast of south-east Australia will likely continue through the southern hemisphere summer 2023–24. The forecast of unusually warm sea surface temperatures (SSTs) in the Tasman Sea may contribute to an increased chance of above average summer rainfall over parts of Australia. Warm anomalies in the Coral Sea are forecast to persist into early 2024. 

Globally, in the ERSSTv5 dataset, SSTs for April to November 2023 were warmest on record (since 1900) for their respective months. August and September SSTs were also globally warmest and second-warmest, respectively, for any month.

For the week ending 17 December 2023, sea surface temperatures (SSTs) were warmer than average across almost all of the equatorial region of the tropical Pacific Ocean. Anomalies were more than 1.2 °C warmer than average east of the Date Line, excluding regions along the Peruvian coast, south of the equator, which were close to average. Anomalies were more than 2 °C warmer than average in some smaller areas of the central and eastern tropical Pacific. Compared to last fortnight, warm anomalies have generally decreased, particularly along the equator and the far eastern Pacific.

Closer to Australia, warm SST anomalies up to 4 °C above average persist off the south-east coast, with anomalies up to 1.2 °C above average extending over the western half of the Tasman Sea. There were also warm SST anomalies off the north-west and south-west coasts of Australia, mostly up to about 1.2 °C above average. Compared to last fortnight, the warm anomalies in the Tasman Sea have slightly increased.

A small area of cool anomalies up to 1.2 °C below average has appeared off the central Queensland coast as a result of tropical cyclone Jasper. Tropical cyclones cool the ocean surface through mechanisms such as increased upwelling of cooler waters from below the surface, and increased wind-induced evaporation.

The latest values of the three NINO indices for the week ending 17 December 2023 were: NINO3, +1.61 °C; NINO3.4, +1.61 °C; and NINO4, +1.33 °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–, 60– and 90-day Southern Oscillation Index (SOI) values for the period ending 17 December 2023 were −1.3, −5.2 and −6.3, respectively. The positive trend of the SOI in the recent fortnight has been in large part due to the development of tropical cyclone Jasper in the Coral Sea, which has resulted in low pressure anomalies over northern Australia.

Sustained negative values of SOI below −7 typically indicate El Niño, while sustained positive values above +7 typically indicate La Niña.

Trade winds for the 5 days ending 17 December 2023 were close to average over the equatorial Pacific.

Trade winds for November 2023 have been slightly weaker to weaker than average across the western equatorial Pacific. They were stronger than average over the central and western Pacific during the second half of November and weaker than average over the central equatorial Pacific for most of September to November.

During El Niño, there is typically a sustained weakening, or even reversal, of trade winds across much of the tropical Pacific, while during La Niña, there is a sustained strengthening of trade winds.

The Madden–Julian Oscillation (MJO) is currently over the western Pacific. International climate models suggest it will move eastwards across the western Pacific over the coming days and weaken, potentially re-strengthening in the Western Hemisphere and Africa after a week. While the MJO maintains its strength over the western Pacific, it increases the chance of above average rainfall over northern Australia. However, in the western hemisphere and Africa region, the MJO typically decreases the chance of above average rainfall.

The positive Indian Ocean Dipole (IOD) event remains active but is steadily weakening. The IOD index is +0.98 °C for the week ending 17 December 2023. The weekly IOD index values for this event have been the second-highest on record since the Bureau SST dataset began in 2001, with the highest on record being during the strong positive IOD event of 2019. To date, the highest weekly IOD index for the current event was +1.92 °C for the week ending 15 October.

Sea surface temperatures (SSTs) for the week ending 17 December were warmer than average across much of the western half of the tropical Indian Ocean, as well as other parts of the basin south of 15°S. Conversely, the eastern pole of the IOD was cooler than average, with a small area of cooler waters extending off the coast of Java, Indonesia. A gradient between the western and eastern tropical Indian Ocean is still apparent but weakening, with a notable warming of the eastern pole, and some cooling of the western pole. This gradient between cooler east and warmer west is typical of a positive IOD.

IOD events typically break down at the end of spring as the monsoon trough shifts south into the southern hemisphere. The breakdown this year has been later than usual, likely due to the strength of this event and the active El Niño. International climate models surveyed by the Bureau suggest the positive IOD is likely to continue to ease over the coming weeks, with the majority of models indicating the IOD index will fall below +0.4 °C in January.

When a positive IOD persists into December, the usual dry and warm signal associated with spring tends to persist, but typically to a lesser degree. However, the small number of years where a positive IOD has persisted into December means there is greater uncertainty on its typical impacts.

Outgoing Longwave Radiation (OLR) around the equatorial Date Line is currently below average (indicating increased cloudiness). OLR has been mostly below average since mid-September 2023.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies).

The 4-month sequence of equatorial Pacific sub-surface temperature anomalies (to 30 November 2023) shows warm anomalies across most of the top 100 m of the equatorial Pacific band, with the exception of the western Pacific, where waters are closer to average. Anomalies increase in magnitude eastwards across the equatorial Pacific, with the central Pacific up to around 2 °C warmer than average, and the eastern Pacific up to around 4 °C warmer than average. A small region is more than 5 °C warmer than average.

Warm anomalies have persisted in the central and eastern Pacific between the surface and 200 m depth. Compared to October, the magnitude of warm anomalies has slightly increased, except in the far eastern Pacific, where it has decreased.

West of the Date Line, there are cool anomalies between 100 and 250 m depth. These cool anomalies have steadily increased in magnitude and extent since September.

For the 5 days ending 17 December 2023, sub-surface temperatures were warmer than average across the upper levels of the equatorial Pacific, east of the Date Line, between the surface to around 100 m depth in the eastern Pacific, and between the surface to around 150 m depth in the central Pacific. Much of this region was more than 2 °C warmer than average, with anomalies more than 5 °C warmer than average between 125°W and 100°W at around 50 m depth.

Compared to last fortnight, the magnitude of warm anomalies in the central Pacific have decreased. Cool anomalies have continued to increase in extent in the western Pacific, at depths 100 to 250 m below the surface.

The Bureau continues to routinely report on the major climate influences on Australia's weather. The influence of drivers such as El Niño and the Indian Ocean Dipole tend to be weaker over the summer months. As has been reported throughout 2023, the model-based long-range forecast of rainfall and temperature provides the best guidance of likely conditions for the months ahead.  Long-range forecast guidance will be updated on Thursday 21 December.

The long-range forecast for Australia for January indicates an increased chance of above median rainfall for parts of Queensland, NSW and Victoria, and more neutral rainfall chances across much of the country. Chances favour drier than average conditions for western parts of WA and the Top End of the NT.

The long-range forecasts increase the chances of drier conditions across many parts of Australia for February and March, but chances are more neutral across the three months for regions that typically experience easterly flow during this time.

Warmer days and nights are very likely for almost all of Australia with unusually warm daytime and night time temperatures at least 2 times more likely than usual.

The Bureau's climate model accounts for all oceanic and atmospheric influences on Australia's climate when generating its forecasts, as well as the influence of climate change.

Current state of climate drivers:

• The Southern Annular Mode (SAM) is likely to remain positive for at least the next two to three weeks. During summer, a positive SAM historically increases the chance of above average rainfall for parts of eastern NSW, south-eastern Queensland, eastern Victoria, and north-east Tasmania, but increases the chance of below average rainfall for western Tasmania. Rainfall increases are due to the positive SAM shifting westerly winds further south, increasing onshore flow over south-east Australia.
• The El Niño event continues in the tropical Pacific –  the typical drying influence of El Niño on Australia's climate usually reduces during summer, especially in the east. As we have seen this year and in the historical data, high-impact rainfall events can occur during El Niño years, particularly during October to April when severe storm frequency peaks, even when the season is dry overall.
• A positive Indian Ocean Dipole (IOD) event remains active, but is weakening steadily. IOD events typically breakdown as the monsoon trough shifts south into the southern hemisphere, typically at the end of spring. Given the current strength of this event, the breakdown this year has been later than usual. Model forecasts suggest the positive IOD is likely to continue to ease over the coming weeks, with the majority indicating the IOD index will fall below +0.4 °C in January.
• The Madden–Julian Oscillation (MJO) is currently over the western Pacific. International climate models suggest it will move eastwards across the western Pacific over the coming days and weaken, potentially re-strengthening over the Western Hemisphere and Africa after a week. While the MJO maintains its strength over the western Pacific, it increases the chance of above average rainfall over northern Australia. However, in the western hemisphere and Africa region, the MJO typically decreases the chance of above average rainfall.
• Global warming – global sea surface temperatures (SSTs) were highest on record for their respective months during April to November. Forecast unusually warm sea surface temperatures (SSTs) in the Tasman Sea may also be contributing to a chance of above median summer rainfall over parts of Australia.

Australia's climate has warmed by 1.48 ± 0.23 °C since national records began in 1910. There has been an increase in extreme heat and fire weather associated with the warming. There has also been a trend towards a greater proportion of rainfall from high intensity, short duration rainfall events, especially across northern Australia.

The Southern Annular Mode (SAM) is currently positive and is likely to remain positive for at least the next two to three weeks. During summer, positive SAM increases the chance of above average rainfall for parts of eastern NSW, south-eastern Queensland, eastern Victoria, and north-eastern Tasmania, but increases the chance of below average rainfall for western Tasmania. The increased chance of rainfall is due to the positive SAM shifting westerly winds further south, increasing onshore flow over south-east Australia.

International model forecasts indicate warming of the equatorial Pacific has likely peaked, although sea surface temperatures are expected to remain above El Niño thresholds into the southern hemisphere autumn 2024. The 2023 El Niño event is tracking around at least moderate strength. 

The long-range forecast for the southern hemisphere summer indicates rainfall is likely to be below median across much of northern and western Australia. The influence of El Niño on Australian rainfall usually reduces during summer, especially in the east; however, below median rainfall is still often observed in the north-east. Additionally, high-impact rainfall events can occur during El Niño years, particularly during October to April when severe storm frequency peaks and there is an overlap with the tropical cyclone season (November to April).