Southern hemisphere monitoring history

Australian climate is influenced by sea surface temperature and atmospheric patterns in regions including Pacific, Indian and Southern oceans. Specific regions are monitored, as they can indicate the presence, or potential development, of El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) phases and different states of the Southern Annular Mode (SAM).

SST anomalies for the latest week

Map for selected period

About these maps

Sea surface temperature (SST) data

The weekly and monthly datasets are formed from weekly or monthly averages of daily SST values, and are updated either weekly or monthly in near real-time. The daily values are obtained from interpolated (gap-free) analyses on a 0.25° degree latitude by 0.25° degree longitude grid of the temperature of the uppermost 10 metres of the ocean under well-mixed conditions, based on observations from both in-water instruments and satellites. As observations are not always available within the specified time interval for all areas covered, the daily analysis systems uses 'statistical interpolation' to fill in the gaps using a weighted combination of the previous daily SST analysis and previous weekly SST analysis.

The temperature estimate is generally considered to be at approximately 0.2 metres depth (the depth of drifting buoys). However, as the observations used for the analysis have been selected for only well-mixed conditions, these temperatures are similar to temperatures down to approximately 10 metres. The maps provide SST analysis values for each 0.25° degree of latitude and longitude (approximately 28 km).

The observations used to derive the global daily SST analyses are obtained from drifting buoys, moored buoys, ships, and infrared radiometers aboard Polar-Orbiting Environmental Satellites operated by the National Oceanographic and Atmospheric Administration (NOAA) and the European Space Agency (ESA). In order to fill in some of the data gaps due to satellite infrared sensors that cannot penetrate cloud, they also incorporate SST observations from microwave sensors on polar-orbiting satellites operated by the Japan Aerospace Exploration Agency (JAXA).

Pacific Ocean

The Pacific Ocean is monitored closely for the current state of the El Niño–Southern Oscillation (ENSO). ENSO refers to the oscillation between warmer (El Niño) and cooler (La Niña) states of the central and eastern tropical Pacific region. ENSO is considered one of the dominant modes of climate variability in Australia. El Niño has historically brought drier conditions during winter and spring, and La Niña wetter conditions, with the influence from La Niña also often extending into summer. The influence of each individual event varies, particularly in conjunction with other climate indicators such as the Indian Ocean Dipole (IOD).

The ENSO signal is characterised by sea surface temperature (SST) patterns in the central and eastern tropical Pacific. Cooler than average SSTs are associated with La Niña, while warmer SSTs are associated with El Niño.

Weekly and monthly sea surface temperature

Weekly temperature anomalies in the tropical Pacific
Select to see full-size map showing temperature anomalies in the tropical Pacific
Monthly temperature anomalies in the tropical Pacific
Map showing temperature anomalies in the tropical Pacific

Cooler than average waters beneath the surface of the central and eastern tropical Pacific can be a sign of La Niña development, while warmer than average waters can be a sign of El Niño development.

5-day and monthly sub-surface temperatures

5-day sub-surface temperatures and anomalies
Select to see full-size plot of sub-surface temperatures and anomalies.
Monthly sub-surface temperature anomalies
Select to see full-size plot of sub-surface temperature anomalies

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

Trade winds

5-day SST and wind anomaly from TAO/TRITON
Select to see full-size map of 5-day SST and wind anomaly from TAO/TRITON.

Outgoing longwave radiation (OLR), the amount of longwave radiation being emitted to space, can be used as an indicator of cloudiness. Equatorial cloudiness near the International Date Line typically increases during El Niño (as indicated by below average OLR) and decreases during La Niña (as indicated by above average OLR).

Cloudiness near the Date Line

Graph of Outgoing longwave radiation (OLR) totals over the dateline
Select to see full-size graph of OLR totals over the dateline.

The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperatures between the eastern and western tropical Indian Ocean. The influence of the IOD varies in conjunction with other climate indicators such as the El Niño–Southern Oscillation (ENSO).

During a negative IOD, waters are typically warmer than average in the eastern parts of the tropical Indian Ocean and cooler than average in the west. During a positive event, the reverse occurs, with cooler than average waters in the eastern parts of the tropical Indian Ocean and warmer in the west. Specific regions are monitored in the eastern and western Indian Ocean to identify IOD event development.

Weekly and monthly sea surface temperature

The Southern Annular Mode (SAM) refers to the north-south movement of rain-bearing westerly winds and weather systems in the Southern Ocean, compared to the usual seasonal position. A positive SAM refers to a southward shift while a negative SAM refers to an northward shift. The typical impact on Australian rainfall from positive and negative phases of SAM depends on the time of year and interaction with other climate indicators such as El Niño or La Niña.

Sustained values of the SAM index above +1 indicate a positive SAM event, while sustained values below -1 indicate a negative SAM event.

SAM history is available in the monitoring graphs


History

Tropical Pacific continues to warm with a transition to El Niño likely during winter

  • The El Niño–Southern Oscillation (ENSO) is currently neutral although there are signs of El Niño development. The latest relative Niño 3.4 index value for the week ending 24 May 2026 is +0.67 °C, within the ENSO-neutral range (−0.80 to +0.80 °C). There has been substantial warming in this region in recent weeks, with the index warming by about 0.2 °C in the past fortnight and by 1.3 °C since early March. Significant warmth in the sub-surface suggests further warming of SSTs is likely in the coming weeks.
  • All models, including the Bureau's, forecast the tropical Pacific to continue warming in the coming months, with SSTs likely to reach El Niño thresholds during early winter. For El Niño to be considered established, a corresponding atmospheric response must be observed, including large-scale changes in pressure, trade winds, and cloudiness patterns.
  • Atmospheric indicators, such as trade winds, pressure and cloud patterns in the tropical Pacific remain consistent with ENSO-neutral conditions but are also trending towards an El Niño state.
  • As of 24 May 2026, the 30-day Southern Oscillation Index (SOI) is −13.4. The 60-day and 90-day SOI index values are −11.8 and −0.9, respectively. The SOI is a point-based index, between Darwin and Tahiti, that may not fully represent broad scale changes in atmospheric circulation patterns.
  • There remains some uncertainty in the likely strength of this El Niño event. Models indicate it will be at least moderate in strength, with the possibility of a strong event, based on the extent of warming in the central tropical Pacific.
  • A strong El Niño signal in the Nino3.4 region does not necessarily mean strong impacts on Australia's climate, as ENSO is only one of many factors that can influence Australia’s seasonal weather and climate.
  • The Madden–Julian Oscillation is in the Western Pacific and forecasts suggest it is likely to strengthen and continue moving eastwards into the Western Hemisphere regions during late May and early June. If this occurs, associated westerly wind anomalies over the western Pacific could support further warming of tropical Pacific, reinforcing El Niño development.
  • The Indian Ocean Dipole (IOD) is currently neutral. As of 24 May 2026, the IOD index is −0.34 °C. There is substantial uncertainty in the forecast state of the IOD. Most models indicate the IOD is likely to remain neutral until at least early winter, with the development of a positive IOD event possible during winter–spring. Model forecasts show a large variation in both timing and strength of this potential event.
  • The sea surface temperature (SST) analysis for the week ending 24 May 2026 shows waters being close to average around much of Australia except to the south-east and south-west where SSTs are above average. Waters are especially warm along the New South Wales and eastern Tasmania coasts (peaking at around 3 to 4 °C above average).
  • The Southern Annular Mode (SAM) index is positive as at 23 May 2026. It is forecast to return to neutral during early-to-mid June.
  • The long-range forecast provides the best guidance on likely conditions in the coming months, and uses the Bureau's climate model to take into account all influences from the oceans and atmosphere.

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.

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.

Product code: IDCKGEWW00

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