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 SST maps are produced from weekly or monthly averages of daily gridded SST analyses from the Bureau's GAMSSA dataset. They are obtained from interpolated (gap-free) analyses on a 0.25° latitude by 0.25° longitude grid.

The temperature estimate is generally considered to be at approximately 0.2 metres depth (the depth of drifting buoys). For well-mixed conditions such as the locations of observational buoys, these temperatures are similar to temperatures down to approximately 10 metres.

As observations are not always available within the specified time interval for all areas covered, statistical interpolation of the daily SST grid is used to fill in the gaps using a weighted combination of available observations, the previous daily SST analysis and previous weekly SST analysis. The maps provide SST analysis values for each 0.25° of latitude and longitude (approximately 28 km at the equator).

The data is masked over land, near coastlines and in sea ice regions, where SST data is unavailable or unreliable. On the maps, 'No data' refers to where the data is masked.

Observations used

The observations used to derive the daily global 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, the analyses also incorporate data from microwave sensors on polar-orbiting satellites operated by the Japan Aerospace Exploration Agency (JAXA).

For more information on the GAMSSA dataset see:

Historical monthly data (ERSST v6 dataset)

The monthly SST data time-series is based on the NOAA Extended Reconstructed Sea Surface Temperature Version 6 (ERSSTv6) data from the NOAA/OAR/ESRL PSL data archive USA. ERSSTv6 is a global monthly analysis of sea surface temperatures, extending from January 1850 to the present, on a 2° x 2° latitude-longitude grid.

ERSSTv6 incorporates observations from ships, drifting and moored buoys, and Argo profiling floats. Its input data include the International Comprehensive Ocean Atmosphere Data Set (ICOADS) Release 3.0.2, Argo observations from the Argo Global Data Assembly Centre, and sea-ice concentration data from HadISST2 for 1850‐2015 and NCEP from 2016 onwards. Very recent observations have not been subjected to the same degree of quality control as past data. ERSSTv6 does not include any satellite data, so recent SSTs can be better compared with historical periods.

For more information on the ERSSTv6 dataset see: Huang et al. (2025a) and Huang et al. (2025b).

Early SST analyses

Before the satellite era, which began in the early 1980s, the primary source of SST observations was from ships. The frequency of these observations was too low to produce a useful daily or weekly dataset for most of the world's oceans, so they typically have a much shorter periods than monthly SST datasets.

In addition, IOD and ENSO event identification using early monthly SST analyses is less accurate due to the less complete coverage. For our climate indices, we consider ENSO indices to be less reliable before 1950, and for the IOD prior to 1960.

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

La Niña in the tropical Pacific; negative Indian Ocean Dipole weakening

  • The sea surface temperature (SST) analysis for the week ending 7 December 2025 shows warmer than average waters extend off much of eastern and south-western Australia. A broad area exceeding 1.2 °C above average extends across much of the Coral Sea and along parts of the east coast. Off the south-east coast, waters are cooler than average.
  • SSTs in the Australian region were the second warmest on record for November, with forecasts for December to February indicating warmer-than-average SSTs are likely to continue for much of the region, especially to Australia's east. Warmer oceans can provide increased moisture and energy, that can enhance the severity of storms, cyclones and rain systems.
  • La Niña is underway in the tropical Pacific. There are signs the tropical Pacific ocean and atmosphere are coupled, meaning they are currently acting to reinforce and sustain the La Niña pattern. The latest relative Niño3.4 SST index value for the week ending 7 December 2025 is −0.74 °C. Sustained values below −0.80 °C are consistent with a La Niña pattern. Weekly values of the relative Niño3.4 index have been fluctuating around the La Niña threshold since mid-to-late September.
  • Atmospheric indicators, such as trade winds, pressure and cloud patterns over the equatorial central Pacific, have shown consistent signs of La Niña. As of 7 December 2025, the 30-day Southern Oscillation Index (SOI) has dropped to +2.2 (below the La Niña threshold of +7), due to tropical activity near Tahiti over the past week. Transient tropical systems can affect the SOI during the summer months and are not necessarily a reflection of the large-scale state of the climate system. Trade wind strength and cloud patterns have been indicative of La Niña since at least mid-to-late September.
  • Over the last fortnight, westerly wind anomalies associated with an active pulse of the Madden–Julian Oscillation have developed over the tropical Pacific. These winds typically act to warm sea surface temperatures and may signal the early stages of a weakening La Niña pattern, particularly as some forecasts suggest these westerly winds anomalies could persist into the coming fortnight.
  • The Bureau's model currently predicts that tropical Pacific Ocean temperatures are likely to remain at La Niña levels until early 2026 before returning to neutral, broadly consistent with most international models, but earlier than the typical ENSO event decay.
  • The negative Indian Ocean Dipole (IOD) event remains active but has been weakening since late October. The latest index value is −0.63 °C for the week ending 7 December 2025.
  • The Bureau's model predicts a return to a neutral IOD in December. This is consistent with most international models assessed and the historically observed IOD life cycle.
  • The Southern Annular Mode (SAM) index is negative as at 6 December 2025, and has been negative for the past week and a half. It is forecast to remain negative over the coming week and a half. Thereafter, there is a range of possible outcomes, meaning less clarity in the SAM phase for the last week of December.
  • The long-range forecast provides the best guidance on likely conditions in the coming months, using 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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