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

Sea surface temperatures (SSTs) for September 2023 were warmer than average over almost all of the equatorial Pacific Ocean. SST anomalies more than 0.8 °C warmer than the long term average (1961–1990) were present over much of the Pacific between 10°S and 10°N, increasing to more than 3 °C warmer than average in the eastern tropical Pacific. Much of the central southern Pacific was also warmer than average for September.

Compared to August, warm anomalies have decreased slightly in strength in the eastern and south-west Pacific.

Warm SST anomalies also continued in the southern Tasman Sea, between south-east Australia and New Zealand, but have decreased compared to last month. Warm anomalies have also decreased in the Coral Sea, especially off the northern Queensland coast. Patches of warmer than average SSTs remain in the waters south-west and north-west of Western Australia.

Globally, April to September 2023 SSTs were warmest on record (since 1900) for their respective months. In the ERSSTv5 dataset, August 2023 SSTs were also the warmest globally for any month since observational records began in 1854, with September 2023 being the second-warmest.

For the week ending 22 October 2023, sea surface temperatures (SSTs) were warmer than average across almost all the equatorial region of the tropical Pacific Ocean. Anomalies were more than 1.2 °C warmer than average east of 165°E, increasing to more than 3 °C warmer than average in small areas of the eastern tropical Pacific. Compared to last fortnight, there has been a slight increase in the strength of warmth in the eastern tropical Pacific and around the equatorial Date Line.

Closer to Australia, warm anomalies up to 2 °C above average persist off the coasts of south-east Australia, extending into the western Tasman Sea. There were also warm SST anomalies off most of the coastline of Western Australia, with a small patch off the Ningaloo Coast being up to 3 °C above average.

The latest values of the three NINO indices for the week ending 22 October 2023 were: NINO3, +1.92 °C; NINO3.4, +1.59 °C; and NINO4, +1.48 °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 22 October 2023 were −8.3, −12.0 and −12.1, respectively.

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 22 October 2023 were weaker than average across the western equatorial Pacific, with winds west of the Date Line reversed from their usual easterly direction. Tropical cyclone Lola has likely had an influence on this pattern. Trade winds were also slightly weaker than average across the central equatorial Pacific.

Trade winds for October 2023 have been slightly weaker to weaker than average across most of the equatorial Pacific.

During El Niño, there is 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 weak. Most surveyed models indicate it will strengthen in the coming week. However, there is disagreement between models regarding the location of the pulse. Some models suggest the Western Pacific while others forecast development of the MJO over the eastern Pacific or tropical Americas regions.

The positive Indian Ocean Dipole (IOD) is underway. The IOD index is +1.79 °C for the week ending 22 October. The weekly IOD index values for this positive IOD event are the second-highest since records for the Bureau SST dataset began in 2001, with the highest values on record having occurred during the strong positive IOD event of 2019.

Sea surface temperatures (SSTs) for the week ending 22 October show warmer than average waters in much of the western half of the tropical Indian Ocean, as well as south of 15°S. Conversely, the eastern pole of the IOD was cooler than average, with a notable area of cooler waters extending off the coast of Java. This shows a clear gradient between the western and eastern tropical Indian Ocean that is typical of a positive IOD. Compared to last fortnight, the cooling has contracted slightly, while warm anomalies south of 15°S have increased in strength and extent, including forming off the western coast of Australia.

All international climate models surveyed by the Bureau suggest the positive IOD event is likely to continue into at least December. A positive IOD typically leads to reduced spring rainfall for central and south-east Australia. When a positive IOD and El Niño occur together, their drying effect is typically stronger and more widespread across Australia.

Outgoing Longwave Radiation (OLR) around the equatorial Date Line has been mostly below average since mid-September 2023, indicating above average cloudiness. The above average cloudiness over the past week has likely had a strong influence from the presence of tropical cyclone Lola in the region.

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 19 October 2023) shows warm anomalies across most of the top 100 m of the equatorial Pacific band, except in the far west. Anomalies increase in magnitude eastwards across the equatorial Pacific band, with the far west close to average and the eastern Pacific more than 2.5 °C warmer than average.

The past 4 months have seen sub-surface heat shift towards the surface. Compared to July 2023, warm sub-surface anomalies in the eastern Pacific have decreased slightly, while increasing slightly near the Date Line. In the western Pacific, temperatures have decreased such that most of the water column is now close to average. Below average temperatures have started to appear between 125 m and 250 m depth west of 165°E.

For the 5 days ending 22 October 2023, sub-surface temperatures were warmer than average across the upper levels of the equatorial Pacific between the surface to around 100 m depth in the eastern Pacific, and between the surface to around 150 m depth in the western Pacific. Much of this region was more than 2 °C warmer than average, with anomalies more than 4 °C warmer than average east of 130°E.

Compared to last fortnight, warm anomalies in the eastern Pacific have decreased in strength while there has been a slight expansion of warmth in the western Pacific.

An El Niño and a positive IOD are underway.

Oceanic indicators exhibit a clear El Niño state. Central and eastern Pacific sea surface temperatures (SSTs) continue to exceed El Niño thresholds, with warmer than average waters beneath the surface supporting the warmth at the surface. Models indicate some further warming of central to eastern Pacific SSTs is likely, with SSTs remaining above El Niño thresholds into the early southern hemisphere autumn 2024.

Broadscale pressure and cloudiness patterns over the Pacific reflect El Niño. Trade wind strength over the past fortnight has been weaker than average over most of the Pacific.

El Niño typically leads to reduced spring and early summer rainfall for eastern Australia, and warmer days for the southern two-thirds of the country.

A positive Indian Ocean Dipole (IOD) is underway. All models indicate that this positive IOD will likely be sustained to at least December. A positive IOD typically leads to reduced spring rainfall for central and south-east Australia and can increase the drying influence of El Niño.

When a positive IOD and El Niño occur together, their drying effect is typically stronger and more widespread across Australia. 

The Madden–Julian Oscillation (MJO) is currently weak. Most surveyed models indicate it will strengthen in the coming week. However, there is disagreement between models regarding the location of the pulse. Some models suggest the Western Pacific while others forecast development of the MJO over the eastern Pacific or tropical Americas regions.

The Southern Annular Mode (SAM) index is currently neutral with forecasts indicating it will remain mostly neutral over the coming fortnight.

The long-range forecast for Australia indicates warmer than average conditions are likely across Australia from November to January with below average rainfall across much of Australia excluding parts of the southeast. The Bureau's climate model takes into account all influences from the oceans and atmosphere when generating its long-range forecasts.

Global warming

Global warming continues to influence Australian and global climate. Global sea surface temperatures (SSTs) were warmest on record for their respective months during April to September 2023.

Australia’s climate has warmed by an average of 1.48 ± 0.23 °C since national records began in 1910. There has also been a trend towards a greater proportion of rainfall from high intensity, short duration rainfall events, especially across northern Australia. This is due to a combination of natural variability on decadal timescales and changes in large-scale circulation caused by an increase in greenhouse gas emissions.

The Southern Annular Mode (SAM) index is currently neutral with forecasts indicating it will remain mostly neutral over the coming fortnight. During spring, a neutral SAM is associated with typical climate conditions for Australia.

Central and eastern Pacific sea surface temperatures (SSTs) currently exceed El Niño thresholds. International climate models suggest some further warming of the central and eastern tropical Pacific Ocean is likely. All surveyed models indicate SSTs will remain above El Niño thresholds into early southern hemisphere autumn, 2024.

Closer to Australia, Bureau 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 into at least southern hemisphere summer 2023–24.

El Niño typically increases the chance of below average winter–spring rainfall in eastern Australia and warmer than average days for the southern two-thirds of Australia.