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

Sea surface temperatures (SSTs) for July 2023 were warmer than average over most of the equatorial Pacific Ocean. SST anomalies more than 0.8 °C warmer than the 1961–1990 average were present over much of the tropical Pacific, increasing to more than 2 °C warmer than average in the eastern tropical Pacific. Much of the southern Pacific was also warmer than average for July.

Compared to June, warm anomalies have strengthened across the central and eastern equatorial Pacific.

Warm SST anomalies also continued in the southern Tasman Sea, between south-east Australia and New Zealand, but have decreased in compared to last month. However, warm anomalies have spread to surround most of south-eastern Australia. Cool anomalies have developed around much of western Australia. In the ERSSTv5 dataset, Coral Sea SSTs were 3rd warmest on record for July, with an anomaly of 0.93 °C above average. 

Globally, April, May, June, and July 2023 SSTs were the warmest on record (since 1900) for their respective months. In the ERSSTv5 dataset, the global area-average SSTs for April, May, June, and July were respectively 0.69 °C, 0.70 °C and 0.71 °C and 0.80 °C above their 1961–1990 averages. While March is typically when SSTs are highest, July 2023 has also come in as equal-highest on record for any month since 1900, on par with March 2016, according to the ERA5 reanalysis.

For the week ending 13 August 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 2 °C warmer than average in the eastern tropical Pacific, increasing to more than 4 °C warmer than average in isolated areas off the South American coast. Only a very small area of the far western equatorial Pacific was close to average. Compared to two weeks ago, some of the warmth in the tropical Pacific has shifted westwards, with slightly higher SST anomalies in the central Pacific compared to two weeks ago. Atypical to a normal El Niño pattern, warm anomalies continue to persist in the south-west Pacific from the south-east of Papua New Guinea extending south-eastwards. However, they have decreased in strength over the past fortnight.

Closer to Australia, SST anomalies of more than 0.8 °C warmer than average persist along the east Australian coastline, wrapping around Tasmania and Victoria. Patchy warm anomalies are also present near south-west WA and parts of northern Australia. Warm SST anomalies also persist in the southern Tasman Sea, from south-east Australia to the South Island of New Zealand, although these have weakened over the past fortnight. Cool SST anomalies around the western coastline of Australia have weakened over the past fortnight, with only small, isolated areas of more than 0.4 °C cooler than average remaining.

The latest values of the three NINO indices for the week ending 13 August 2023 were: NINO3 +1.71 °C, NINO3.4 +1.14 °C and NINO4 +0.94 °C.

Persistent NINO3 or NINO3.4 values cooler than +0.8 °C are typical of El Niño, while persistent values warmer than −0.8 °C typically indicate La Niña.

The 30-day Southern Oscillation Index (SOI) for the period ending 13 August 2023 was −13.4, with the index decreasing rapidly by 9.1 over the past fortnight to moderate strength negative values (more El Niño-like). This recent decrease is likely due to local conditions over Australia, with most of the SOI signal attributable to conditions in Darwin (+2.3 hPa anomaly compared to +0.3 hPa at Tahiti). El Niño is associated with higher than average pressure over Australia and lower than average pressure over Tahiti. The 60-day SOI and the 90-day SOI were −5.3 and −7.6, respectively.

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

Trade winds for the 5 days ending 13 August 2023 were weaker than average over the far western tropical Pacific, but closer to average elsewhere.

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 in the western hemisphere and currently weak. Climate models surveyed indicate a high amount of uncertainty in the location and strength of the MJO over the next 2 weeks. While a majority of models expect the MJO to remain weak, some forecast a moderately strong MJO pulse over the Pacific Ocean in the coming week, which could assist the development of conditions towards an El Niño event.

The Indian Ocean Dipole (IOD) is currently neutral. The IOD index for the week ending 13 August 2023 was +0.32 °C, which is within neutral bounds (between −0.40 °C and +0.40 °C).

Weekly sea surface temperatures (SSTs) for the period ending 13 August were above average across large areas of the tropical and southern Indian Ocean, especially in the mid-latitudes where anomalies were up to 2 to 3 °C warmer than average in isolated areas. The western pole of the IOD has warmed slightly compared to two weeks ago (more positive IOD-like). The eastern pole of the IOD remains similar in strength compared to two weeks ago.

SSTs are close to average to the west and north-west of Australia, extending up to Indonesia.

All international climate models surveyed by the Bureau suggest a positive IOD event is likely to develop in early spring. A positive IOD can supress winter–spring rainfall over much of central and south-east Australia, and if combined with El Niño, the drying effect is typically stronger and more widespread across Australia. 

Cloudiness near the Date Line has fluctuated around average levels since late 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 July 2023) shows warm anomalies across most of the top 150 m of the equatorial Pacific band. Anomalies increase in magnitude eastwards across the equatorial Pacific band, with the far west 0.5 °C warmer than average and the eastern Pacific more than 4 °C warmer than average.

June and July have seen sub-surface heat shift towards the eastern Pacific, between the surface and 150 m depth. Heat has decreased in the western Pacific such that only slightly warm anomalies remain.

For the five days ending 13 August 2023, sub-surface temperatures were warmer than average across the upper levels of the equatorial Pacific sub-surface (between the surface to around 100 m depth in the central and eastern Pacific and between the surface to around 150 m in the west). Anomalies were more than 4 °C warmer than average in a small area in the eastern Pacific, around 50 m depth.

Compared to two weeks ago, warm anomalies in the eastern Pacific have cooled, and those in the west have warmed, with the cooler anomalies at depth weakening over the past two weeks.

The Bureau's El Niño Alert continues, with El Niño development likely during spring. When El Niño Alert criteria have been met in the past, an El Niño event has developed around 70% of the time.

Sea surface temperatures (SSTs) in the tropical Pacific are exceeding El Niño thresholds, with climate models indicating this is likely to continue at least through to early 2024. The past fortnight has seen a decrease in Southern Oscillation Index (SOI) values to moderate negative values (more El Niño-like). However, this strong swing has been due to increased pressure over Australia, with Tahiti close to normal. El Niño is associated with higher than average pressure over Australia and lower than average pressure over Tahiti. Overall, atmospheric indicators suggest the Pacific Ocean and atmosphere are not yet consistently reinforcing each other, as occurs during El Niño events. El Niño typically suppresses winter–spring rainfall in eastern Australia.

The Indian Ocean Dipole (IOD) is currently neutral. Climate model forecasts suggest a positive IOD is likely to develop during spring. A positive IOD typically decreases winter–spring rainfall for much of Australia and can increase the drying influence of El Niño.

The Madden–Julian Oscillation (MJO) is in the western hemisphere and currently weak. Some climate models are forecasting a moderately strong MJO pulse over the Pacific Ocean in the coming week; this could assist development towards El Niño conditions.

The Southern Annular Mode (SAM) index is currently neutral and is expected to remain neutral for the coming fortnight. A neutral SAM is associated with typical climate conditions for Australia.

The current status of the ENSO Outlook and other climate drivers does not change the long-range forecast of warmer and drier conditions across most of southern and eastern Australia from September to November. 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 climates. Global sea surface temperatures were the highest on record for their respective months during April to July 2023, with July also being the equal-highest month on record (according to the ERA5 reanalysis). July 2023 was also the hottest month globally in terms of 2 metre air temperature.

Australia’s climate has warmed by an average of 1.47 ± 0.24 °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. Southern Australia has seen a reduction, by 10 to 20%, in cool season (April to October) rainfall in recent decades. 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, and is expected to remain neutral for the coming three weeks. 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 further warming of the central and eastern tropical Pacific Ocean is likely. All surveyed models indicate SSTs will remain above El Niño thresholds until at least into early 2024. If the atmosphere responds to this warming, an El Niño event would be expected to develop.

El Niño typically suppresses winter–spring rainfall in eastern Australia.