For long-range forecasts of rainfall and temperature for Australia, please see our long-range forecast page. It 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.
The Southern Hemisphere Monitoring page contains information on the broader hemispheric climate state, including the current status of the El Niño–Southern Oscillation and the Indian Ocean Dipole. This information is useful because:
- it can be a source of longer-term predictability, which can provide intelligence that extends beyond the long-range forecast period.
- understanding the long-range forecast is improved through the assessment of its consistency within the broader climate system.
Related: Southern Hemisphere Outlooks
Southern hemisphere monitoring
Pacific, Indian and Southern ocean regions
La Niña in the tropical Pacific; negative Indian Ocean Dipole weakening
- The sea surface temperature (SST) analysis for the week ending 23 November 2025 shows warmer than average waters across much of the Australian region. 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 October, with forecasts for December to February indicating warmer-than-average SSTs are likely to continue in 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.
- Latest assessments of the El Niño–Southern Oscillation (ENSO) indicate La Niña is underway. There are clear signs the tropical Pacific ocean and atmosphere are now coupled, meaning they are acting to reinforce and sustain the La Niña pattern.
- Observations in the tropical Pacific Ocean have been consistent with La Niña conditions since early October. The latest relative Niño3.4 SST index value for the week ending 23 November 2025 is −0.93 °C. Sustained values below −0.8 °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, also show consistent signs of La Niña. As at 23 November 2025, the 30-day Southern Oscillation Index (SOI) is +16.1, while the 90-day SOI value is +8.5. Sustained 90-day SOI values above +7.0 are indicative of La Niña. Trade wind strength and cloud patterns have been indicative of La Niña since at least mid-to-late September.
- Short-term 30-day SOI values are likely more positive due to Severe Tropical Cyclone Fina developing near Darwin from 19 November 2025, lowering surface pressure in the region. Transient tropical systems can affect the short-term SOI during the summer months and are not necessarily a reflection of the state of the climate system.
- 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. This timing aligns with most international models assessed.
- The negative Indian Ocean Dipole (IOD) event remains active but has been weakening steadily over the past three weeks. The latest index value is −0.60 °C for the week ending 23 November.
- The Bureau's model predicts a return to a neutral IOD in December. This is consistent with most international models assessed and the typical IOD life cycle.
- The Southern Annular Mode (SAM) index is neutral as at 21 November 2025. It is forecast to become negative over the coming week. However, there is a broad range in possible outcomes, indicating increased uncertainty into 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
Australian climate is influenced by sea surface temperature and atmospheric patterns in regions including the 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).
About these maps
SST index regions map
The 'SST index regions' overlay map is an approximate diagram. Region boundaries are specified in 'Climate indices' below.
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).
- BoM GAMSSA SST analysis: Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Climate indices
An index is a measure (often a numerical value) that can be representative of a particular pattern or state of a system. Climatologists monitor several indices, some ocean-based and some atmospheric, to provide a quick indication of the state of certain climate variables and climate indicators.
El Niño–Southern Oscillation indices
El Niño and La Niña (collectively referred to as the El Niño–Southern Oscillation or ENSO) are characterised by changes in the equatorial Pacific Ocean. During El Niño, sea surface temperatures (SST) in the central and eastern Pacific Ocean become warmer than average, while during La Niña these SSTs become cooler than average.
Niño indices regions
To monitor the Pacific Ocean for signs of El Niño or La Niña, climatologists use several SST indices. These indices measure the difference between the current sea surface temperature and its long-term (1991–2020) average in several regions located along the equatorial Pacific. The difference is referred to as an anomaly. These regions are labelled Niño1, Niño2, Niño3, Niño3.4 and Niño4 and are used by meteorological agencies around the world.
Relative Niño indices
Traditional Niño index values were used at the Bureau of Meteorology until September 2025. From September 2025, the Bureau uses Relative Niño indices, which measure sea surface temperature anomalies in the tropical Pacific Ocean in the Niño regions, but calculated relative to the global tropical region temperature anomaly. This is to relate the indices more closely to the localised processes associated with ENSO, rather than larger-scale tropical SST features such as global warming.
Example: The Relative Niño3.4 index calculation:
Relative Niño3.4 = S x [(Niño3.4obs – Niño3.4clim) – (Tropical Meanobs – Tropical Meanclim)]
Where Niño3.4obs and Tropical Meanobs are the SST averages over the Niño3.4 region and the 20°S to 20°N tropical mean SST, respectively, while Niño3.4clim and Tropical Meanclim are the climatological values for the appropriate day/month depending on the dataset. S is a scaling factor applied so the variance of the relative Niño index matches that of the traditional index.
For the analysis of ENSO status, Relative Niño indices are used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). Bureau climatologists cite sustained monthly Relative Niño3 or Niño3.4 index values above +0.8 °C as typical of El Niño conditions, with values of below −0.8 °C as typical of La Niña. These values are approximately one standard deviation from the long-term mean (e.g., around 70% of monthly Niño3.4 values, lie between −0.8 °C and +0.8 °C).
The Niño regions in the Pacific Ocean, are used to monitor ENSO, with Niño3 and Niño3.4 typically used to identify El Niño and La Niña.
Niño regions cover the following areas:
- Niño1 (far eastern equatorial Pacific): 5–10°S, 90–80°W
- Niño2 (far eastern equatorial Pacific): 0–5°S, 90–80°W
- Niño3 (eastern equatorial Pacific): 5°N–5°S, 150–90°W
- Niño3.4 (central equatorial Pacific): 5°N–5°S, 170–120°W
- Niño4 (western equatorial Pacific): 5°N–5°S, 160°E–150°W
For monitoring of ENSO phases, the value of the Niño indices are often used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). The Bureau cites sustained monthly Niño3 or Niño3.4 values above +0.8 °C as being associated with El Niño, and values below −0.8 °C being associated with La Niña. These values are approximately one standard deviation from the long-term mean (i.e., around 70% of monthly Niño3 values in the historical record, for example, lie between −0.8 °C and +0.8 °C).
Details about: El Niño and La Niña
Southern Oscillation Index (SOI)
The Southern Oscillation Index, or SOI, gives an indication of the state and intensity of ENSO, from an atmospheric perspective. The SOI is calculated using the pressure differences between Tahiti and Darwin.
Sustained negative values of the SOI below −7 often indicate El Niño is active while sustained positive values above +7 are typical of a La Niña.
Technical details
There are a few different methods for calculating the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. The base period used in the SOI calculation is 60 years (1933–1992).
Calculation
Pdiff − Pdiffav
SOI = 10 x -------------------,
SD(Pdiff)
where:
Pdiff = (average Tahiti MSLP for the period) − (average Darwin MSLP for the period),
Pdiffav = long term average of Pdiff for the period in question, and
SD(Pdiff) = long term standard deviation of Pdiff for the period in question.
The multiplication by 10 is a convention to make the final value more readable. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a three-month average being sometimes used. Daily values can also be averaged over a longer period to form a multi-day average. Single-day or weekly values of the SOI are not so useful for information on the current state of the climate, as these values are dominated by the effects of short-term weather variability, and accordingly the Bureau of Meteorology does not issue them. In particular, single-day values can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.
Details about: SOI
The Indian Ocean Dipole index
Indian Ocean Dipole (IOD) phases are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD phases.
The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between SST anomalies in two regions of the tropical Indian Ocean (see map):
IOD regions:
- IOD west: 50°E to 70°E and 10°S to 10°N
- IOD east: 90°E to 110°E and 10°S to 0°S
A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.
For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.
Details about: Indian Ocean Dipole
The Southern Annular Mode index
The Southern Annular Mode, or 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 reasearch paper: Southern annular mode impacts on global ocean surface waves.
Details about: Southern Annular Mode
About the data
Data periods
Daily datasets have a value for every day in their record. Similarly, weekly and monthly (30 day) data sets have values for every week or month (30 days), respectively, in their record.
Sea surface temperature 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° latitude by 0.25° 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° 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).
- BoM GAMSSA SST analysis: Beggs et al. (2011) and Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Early SST data
Before the satellite era (which began in the early 1980s), the primary source of SST data was observations made by ships passing through the region. The frequency of these observations was too low to produce a useful weekly dataset, so it is shorter than the monthly dataset. IOD and ENSO event identification using early SST data has limited accuracy, particularly for the Indian Ocean.
SOI data
Data source: The Bureau maintains a SOI database.
The SOI data includes a long history of monthly pressure readings from Darwin and Tahiti that have been digitised for electronic use. Old daily pressure readings have not yet been digitised, so a shorter dataset is available.
Australian climate is influenced by sea surface temperature and atmospheric patterns in regions including the 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).
Climate index monitoring graphs
The Relative Niño indices (R-Niño) are the Bureau of Meteorology's operational indices for monitoring the oceanic component of the El Nino-Southern Oscillation. Prior to September 2025, the Traditional Niño indices (T-Niño) were used. See 'About these graphs' (below the graphs) for more information. The T-Niño index values are included for comparison and archival purposes.
Graph
About these graphs
Climate indices
An index is a measure (often a numerical value) that can be representative of a particular pattern or state of a system. Climatologists monitor several indices, some ocean-based and some atmospheric, to provide a quick indication of the state of certain climate variables and climate indicators.
El Niño–Southern Oscillation indices
El Niño and La Niña (collectively referred to as the El Niño–Southern Oscillation or ENSO) are characterised by changes in the equatorial Pacific Ocean. During El Niño, sea surface temperatures (SST) in the central and eastern Pacific Ocean become warmer than average, while during La Niña these SSTs become cooler than average.
Niño indices regions
To monitor the Pacific Ocean for signs of El Niño or La Niña, climatologists use several SST indices. These indices measure the difference between the current sea surface temperature and its long-term (1991–2020) average in several regions located along the equatorial Pacific. The difference is referred to as an anomaly. These regions are labelled Niño1, Niño2, Niño3, Niño3.4 and Niño4 and are used by meteorological agencies around the world.
Relative Niño indices
Traditional Niño index values were used at the Bureau of Meteorology until September 2025. From September 2025, the Bureau uses Relative Niño indices, which measure sea surface temperature anomalies in the tropical Pacific Ocean in the Niño regions, but calculated relative to the global tropical region temperature anomaly. This is to relate the indices more closely to the localised processes associated with ENSO, rather than larger-scale tropical SST features such as global warming.
Example: The Relative Niño3.4 index calculation:
Relative Niño3.4 = S x [(Niño3.4obs – Niño3.4clim) – (Tropical Meanobs – Tropical Meanclim)]
Where Niño3.4obs and Tropical Meanobs are the SST averages over the Niño3.4 region and the 20°S to 20°N tropical mean SST, respectively, while Niño3.4clim and Tropical Meanclim are the climatological values for the appropriate day/month depending on the dataset. S is a scaling factor applied so the variance of the relative Niño index matches that of the traditional index.
For the analysis of ENSO status, Relative Niño indices are used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). Bureau climatologists cite sustained monthly Relative Niño3 or Niño3.4 index values above +0.8 °C as typical of El Niño conditions, with values of below −0.8 °C as typical of La Niña. These values are approximately one standard deviation from the long-term mean (e.g., around 70% of monthly Niño3.4 values, lie between −0.8 °C and +0.8 °C).
The Niño regions in the Pacific Ocean, are used to monitor ENSO, with Niño3 and Niño3.4 typically used to identify El Niño and La Niña.
Niño regions cover the following areas:
- Niño1 (far eastern equatorial Pacific): 5–10°S, 90–80°W
- Niño2 (far eastern equatorial Pacific): 0–5°S, 90–80°W
- Niño3 (eastern equatorial Pacific): 5°N–5°S, 150–90°W
- Niño3.4 (central equatorial Pacific): 5°N–5°S, 170–120°W
- Niño4 (western equatorial Pacific): 5°N–5°S, 160°E–150°W
For monitoring of ENSO phases, the value of the Niño indices are often used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). The Bureau cites sustained monthly Niño3 or Niño3.4 values above +0.8 °C as being associated with El Niño, and values below −0.8 °C being associated with La Niña. These values are approximately one standard deviation from the long-term mean (i.e., around 70% of monthly Niño3 values in the historical record, for example, lie between −0.8 °C and +0.8 °C).
Details about: El Niño and La Niña
Southern Oscillation Index (SOI)
The Southern Oscillation Index, or SOI, gives an indication of the state and intensity of ENSO, from an atmospheric perspective. The SOI is calculated using the pressure differences between Tahiti and Darwin.
Sustained negative values of the SOI below −7 often indicate El Niño is active while sustained positive values above +7 are typical of a La Niña.
Technical details
There are a few different methods for calculating the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. The base period used in the SOI calculation is 60 years (1933–1992).
Calculation
Pdiff − Pdiffav
SOI = 10 x -------------------,
SD(Pdiff)
where:
Pdiff = (average Tahiti MSLP for the period) − (average Darwin MSLP for the period),
Pdiffav = long term average of Pdiff for the period in question, and
SD(Pdiff) = long term standard deviation of Pdiff for the period in question.
The multiplication by 10 is a convention to make the final value more readable. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a three-month average being sometimes used. Daily values can also be averaged over a longer period to form a multi-day average. Single-day or weekly values of the SOI are not so useful for information on the current state of the climate, as these values are dominated by the effects of short-term weather variability, and accordingly the Bureau of Meteorology does not issue them. In particular, single-day values can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.
Details about: SOI
The Indian Ocean Dipole index
Indian Ocean Dipole (IOD) phases are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD phases.
The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between SST anomalies in two regions of the tropical Indian Ocean (see map):
IOD regions:
- IOD west: 50°E to 70°E and 10°S to 10°N
- IOD east: 90°E to 110°E and 10°S to 0°S
A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.
For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.
Details about: Indian Ocean Dipole
The Southern Annular Mode index
The Southern Annular Mode, or 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 reasearch paper: Southern annular mode impacts on global ocean surface waves.
Details about: Southern Annular Mode
About the data
Data periods
Daily datasets have a value for every day in their record. Similarly, weekly and monthly (30 day) data sets have values for every week or month (30 days), respectively, in their record.
Sea surface temperature 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° latitude by 0.25° 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° 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).
- BoM GAMSSA SST analysis: Beggs et al. (2011) and Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Early SST data
Before the satellite era (which began in the early 1980s), the primary source of SST data was observations made by ships passing through the region. The frequency of these observations was too low to produce a useful weekly dataset, so it is shorter than the monthly dataset. IOD and ENSO event identification using early SST data has limited accuracy, particularly for the Indian Ocean.
SOI data
Data source: The Bureau maintains a SOI database.
The SOI data includes a long history of monthly pressure readings from Darwin and Tahiti that have been digitised for electronic use. Old daily pressure readings have not yet been digitised, so a shorter dataset is available.
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. 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.
Pacific Ocean
Weekly and monthly sea surface temperature
- See also: Links open in new window
- Animation of recent SST changes
Relative Niño indices
About these graphs
Climate indices
An index is a measure (often a numerical value) that can be representative of a particular pattern or state of a system. Climatologists monitor several indices, some ocean-based and some atmospheric, to provide a quick indication of the state of certain climate variables and climate indicators.
El Niño–Southern Oscillation indices
El Niño and La Niña (collectively referred to as the El Niño–Southern Oscillation or ENSO) are characterised by changes in the equatorial Pacific Ocean. During El Niño, sea surface temperatures (SST) in the central and eastern Pacific Ocean become warmer than average, while during La Niña these SSTs become cooler than average.
Niño indices regions
To monitor the Pacific Ocean for signs of El Niño or La Niña, climatologists use several SST indices. These indices measure the difference between the current sea surface temperature and its long-term (1991–2020) average in several regions located along the equatorial Pacific. The difference is referred to as an anomaly. These regions are labelled Niño1, Niño2, Niño3, Niño3.4 and Niño4 and are used by meteorological agencies around the world.
Relative Niño indices
Traditional Niño index values were used at the Bureau of Meteorology until September 2025. From September 2025, the Bureau uses Relative Niño indices, which measure sea surface temperature anomalies in the tropical Pacific Ocean in the Niño regions, but calculated relative to the global tropical region temperature anomaly. This is to relate the indices more closely to the localised processes associated with ENSO, rather than larger-scale tropical SST features such as global warming.
Example: The Relative Niño3.4 index calculation:
Relative Niño3.4 = S x [(Niño3.4obs – Niño3.4clim) – (Tropical Meanobs – Tropical Meanclim)]
Where Niño3.4obs and Tropical Meanobs are the SST averages over the Niño3.4 region and the 20°S to 20°N tropical mean SST, respectively, while Niño3.4clim and Tropical Meanclim are the climatological values for the appropriate day/month depending on the dataset. S is a scaling factor applied so the variance of the relative Niño index matches that of the traditional index.
For the analysis of ENSO status, Relative Niño indices are used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). Bureau climatologists cite sustained monthly Relative Niño3 or Niño3.4 index values above +0.8 °C as typical of El Niño conditions, with values of below −0.8 °C as typical of La Niña. These values are approximately one standard deviation from the long-term mean (e.g., around 70% of monthly Niño3.4 values, lie between −0.8 °C and +0.8 °C).
The Niño regions in the Pacific Ocean, are used to monitor ENSO, with Niño3 and Niño3.4 typically used to identify El Niño and La Niña.
Niño regions cover the following areas:
- Niño1 (far eastern equatorial Pacific): 5–10°S, 90–80°W
- Niño2 (far eastern equatorial Pacific): 0–5°S, 90–80°W
- Niño3 (eastern equatorial Pacific): 5°N–5°S, 150–90°W
- Niño3.4 (central equatorial Pacific): 5°N–5°S, 170–120°W
- Niño4 (western equatorial Pacific): 5°N–5°S, 160°E–150°W
For monitoring of ENSO phases, the value of the Niño indices are often used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). The Bureau cites sustained monthly Niño3 or Niño3.4 values above +0.8 °C as being associated with El Niño, and values below −0.8 °C being associated with La Niña. These values are approximately one standard deviation from the long-term mean (i.e., around 70% of monthly Niño3 values in the historical record, for example, lie between −0.8 °C and +0.8 °C).
Details about: El Niño and La Niña
Southern Oscillation Index (SOI)
The Southern Oscillation Index, or SOI, gives an indication of the state and intensity of ENSO, from an atmospheric perspective. The SOI is calculated using the pressure differences between Tahiti and Darwin.
Sustained negative values of the SOI below −7 often indicate El Niño is active while sustained positive values above +7 are typical of a La Niña.
Technical details
There are a few different methods for calculating the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. The base period used in the SOI calculation is 60 years (1933–1992).
Calculation
Pdiff − Pdiffav
SOI = 10 x -------------------,
SD(Pdiff)
where:
Pdiff = (average Tahiti MSLP for the period) − (average Darwin MSLP for the period),
Pdiffav = long term average of Pdiff for the period in question, and
SD(Pdiff) = long term standard deviation of Pdiff for the period in question.
The multiplication by 10 is a convention to make the final value more readable. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a three-month average being sometimes used. Daily values can also be averaged over a longer period to form a multi-day average. Single-day or weekly values of the SOI are not so useful for information on the current state of the climate, as these values are dominated by the effects of short-term weather variability, and accordingly the Bureau of Meteorology does not issue them. In particular, single-day values can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.
Details about: SOI
The Indian Ocean Dipole index
Indian Ocean Dipole (IOD) phases are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD phases.
The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between SST anomalies in two regions of the tropical Indian Ocean (see map):
IOD regions:
- IOD west: 50°E to 70°E and 10°S to 10°N
- IOD east: 90°E to 110°E and 10°S to 0°S
A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.
For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.
Details about: Indian Ocean Dipole
The Southern Annular Mode index
The Southern Annular Mode, or 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 reasearch paper: Southern annular mode impacts on global ocean surface waves.
Details about: Southern Annular Mode
About the data
Data periods
Daily datasets have a value for every day in their record. Similarly, weekly and monthly (30 day) data sets have values for every week or month (30 days), respectively, in their record.
Sea surface temperature 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° latitude by 0.25° 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° 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).
- BoM GAMSSA SST analysis: Beggs et al. (2011) and Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Early SST data
Before the satellite era (which began in the early 1980s), the primary source of SST data was observations made by ships passing through the region. The frequency of these observations was too low to produce a useful weekly dataset, so it is shorter than the monthly dataset. IOD and ENSO event identification using early SST data has limited accuracy, particularly for the Indian Ocean.
SOI data
Data source: The Bureau maintains a SOI database.
The SOI data includes a long history of monthly pressure readings from Darwin and Tahiti that have been digitised for electronic use. Old daily pressure readings have not yet been digitised, so a shorter dataset is available.
- See also: Links open in new window
- Monthly SOI graph
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
The Southern Oscillation Index (SOI) refers to the difference in mean sea level pressure (MSLP) anomalies between Tahiti and Darwin. Sustained positive values of the SOI above +7 typically indicate La Niña and represent lower than average MSLP at Darwin and/or higher than average MSLP at Tahiti. Sustained negative values below −7 typically indicate El Niño, and higher than average MSLP at Darwin and/or lower than average MSLP at Tahiti.
Southern Oscillation Index
About these graphs
Climate indices
An index is a measure (often a numerical value) that can be representative of a particular pattern or state of a system. Climatologists monitor several indices, some ocean-based and some atmospheric, to provide a quick indication of the state of certain climate variables and climate indicators.
El Niño–Southern Oscillation indices
El Niño and La Niña (collectively referred to as the El Niño–Southern Oscillation or ENSO) are characterised by changes in the equatorial Pacific Ocean. During El Niño, sea surface temperatures (SST) in the central and eastern Pacific Ocean become warmer than average, while during La Niña these SSTs become cooler than average.
Niño indices regions
To monitor the Pacific Ocean for signs of El Niño or La Niña, climatologists use several SST indices. These indices measure the difference between the current sea surface temperature and its long-term (1991–2020) average in several regions located along the equatorial Pacific. The difference is referred to as an anomaly. These regions are labelled Niño1, Niño2, Niño3, Niño3.4 and Niño4 and are used by meteorological agencies around the world.
The Niño regions in the Pacific Ocean, are used to monitor ENSO, with Niño3 and Niño3.4 typically used to identify El Niño and La Niña.
Niño regions cover the following areas:
- Niño1 (far eastern equatorial Pacific): 5–10°S, 80–90°W
- Niño2 (far eastern equatorial Pacific): 0–5°S, 80–90°W
- Niño3 (eastern equatorial Pacific): 5°N–5°S, 150–90°W
- Niño3.4 (central equatorial Pacific): 5°N–5°S, 120–170°W
- Niño4 (western equatorial Pacific): 5°N–5°S, 160°E–150°W
For monitoring of ENSO phases, the value of the Niño indices are often used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). The Bureau cites sustained monthly Niño3 or Niño3.4 values above +0.8 °C as being associated with El Niño, and values below −0.8 °C being associated with La Niña. These values are approximately one standard deviation from the long-term mean (i.e., around 70% of monthly Niño3 values in the historical record, for example, lie between −0.8 °C and +0.8 °C).
Southern Oscillation Index (SOI)
The Southern Oscillation Index, or SOI, gives an indication of the state and intensity of ENSO, from an atmospheric perspective. The SOI is calculated using the pressure differences between Tahiti and Darwin.
Sustained negative values of the SOI below −7 often indicate El Niño is active while sustained positive values above +7 are typical of a La Niña.
Early monthly pressure readings from Darwin and Tahiti have been digitised for electronic use. Early daily pressure readings have not yet been digitised, so a shorter dataset is available.
Technical details
There are a few different methods for calculating the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. The base period used in the SOI calculation is 60 years (1933–1992).
Calculation
Pdiff − Pdiffav
SOI = 10 x -------------------,
SD(Pdiff)
where:
Pdiff = (average Tahiti MSLP for the period) − (average Darwin MSLP for the period),
Pdiffav = long term average of Pdiff for the period in question, and
SD(Pdiff) = long term standard deviation of Pdiff for the period in question.
The multiplication by 10 is a convention to make the final value more readable. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a year being sometimes used. Daily values can also be averaged over a longer period to form a multi-day average. Single-day or weekly values of the SOI are not so useful for information on the current state of the climate, as these values are dominated by the effects of short-term weather variability, and accordingly the Bureau of Meteorology does not issue them. In particular, single-day values can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.
- Details about:
- About ENSO, El Niño and La Niña
- SOI
The Indian Ocean Dipole index
Indian Ocean Dipole (IOD) phases are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD phases.
The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between SST anomalies in two regions of the tropical Indian Ocean (see map):
IOD regions:
- IOD west: 50°E to 70°E and 10°S to 10°N
- IOD east: 90°E to 110°E and 10°S to 0°S
A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.
For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.
- Details about:
- IOD
- IOD phases
The Southern Annular Mode index
The Southern Annular Mode, or 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.
- Details about:
- About SAM
About the data
Data periods
Daily datasets have a value for every day in their record. Similarly, weekly and monthly (30 day) data sets have values for every week or month (30 days), respectively, in their record.
Sea surface temperature 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° latitude by 0.25° 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° 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).
- BoM GAMSSA SST analysis: Beggs et al. (2011) and Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Early SST data
Before the satellite era, the primary source of SST data was observations made by ships passing through the region. The frequency of these observations was too low to produce a useful weekly dataset, so it is shorter than the monthly dataset. IOD and ENSO event identification using early SST data has limited accuracy, particularly for the Indian Ocean.
SOI data
Data source: Bureau SOI data
The SOI data includes a long history of monthly pressure readings from Darwin and Tahiti that have been digitised for electronic use. Old daily pressure readings have not yet been digitised, so a shorter dataset is available.
- See also: Links open in new window
- Monthly SOI graph
During La Niña, 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
- Data Source: Links open in new window
- TAO/TRITON data
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 Dateline 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
- Details about specific years:
- Past El Niños and La Niñas
- 2010–11 and 2011–12 La Niñas
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
Indian Ocean Dipole index
About these graphs
Climate indices
An index is a measure (often a numerical value) that can be representative of a particular pattern or state of a system. Climatologists monitor several indices, some ocean-based and some atmospheric, to provide a quick indication of the state of certain climate variables and climate indicators.
El Niño–Southern Oscillation indices
El Niño and La Niña (collectively referred to as the El Niño–Southern Oscillation or ENSO) are characterised by changes in the equatorial Pacific Ocean. During El Niño, sea surface temperatures (SST) in the central and eastern Pacific Ocean become warmer than average, while during La Niña these SSTs become cooler than average.
Niño indices regions
To monitor the Pacific Ocean for signs of El Niño or La Niña, climatologists use several SST indices. These indices measure the difference between the current sea surface temperature and its long-term (1991–2020) average in several regions located along the equatorial Pacific. The difference is referred to as an anomaly. These regions are labelled Niño1, Niño2, Niño3, Niño3.4 and Niño4 and are used by meteorological agencies around the world.
The Niño regions in the Pacific Ocean, are used to monitor ENSO, with Niño3 and Niño3.4 typically used to identify El Niño and La Niña.
Niño regions cover the following areas:
- Niño1 (far eastern equatorial Pacific): 5–10°S, 80–90°W
- Niño2 (far eastern equatorial Pacific): 0–5°S, 80–90°W
- Niño3 (eastern equatorial Pacific): 5°N–5°S, 150–90°W
- Niño3.4 (central equatorial Pacific): 5°N–5°S, 120–170°W
- Niño4 (western equatorial Pacific): 5°N–5°S, 160°E–150°W
For monitoring of ENSO phases, the value of the Niño indices are often used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). The Bureau cites sustained monthly Niño3 or Niño3.4 values above +0.8 °C as being associated with El Niño, and values below −0.8 °C being associated with La Niña. These values are approximately one standard deviation from the long-term mean (i.e., around 70% of monthly Niño3 values in the historical record, for example, lie between −0.8 °C and +0.8 °C).
Southern Oscillation Index (SOI)
The Southern Oscillation Index, or SOI, gives an indication of the state and intensity of ENSO, from an atmospheric perspective. The SOI is calculated using the pressure differences between Tahiti and Darwin.
Sustained negative values of the SOI below −7 often indicate El Niño is active while sustained positive values above +7 are typical of a La Niña.
Early monthly pressure readings from Darwin and Tahiti have been digitised for electronic use. Early daily pressure readings have not yet been digitised, so a shorter dataset is available.
Technical details
There are a few different methods for calculating the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. The base period used in the SOI calculation is 60 years (1933–1992).
Calculation
Pdiff − Pdiffav
SOI = 10 x -------------------,
SD(Pdiff)
where:
Pdiff = (average Tahiti MSLP for the period) − (average Darwin MSLP for the period),
Pdiffav = long term average of Pdiff for the period in question, and
SD(Pdiff) = long term standard deviation of Pdiff for the period in question.
The multiplication by 10 is a convention to make the final value more readable. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a year being sometimes used. Daily values can also be averaged over a longer period to form a multi-day average. Single-day or weekly values of the SOI are not so useful for information on the current state of the climate, as these values are dominated by the effects of short-term weather variability, and accordingly the Bureau of Meteorology does not issue them. In particular, single-day values can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.
- Details about:
- About ENSO, El Niño and La Niña
- SOI
The Indian Ocean Dipole index
Indian Ocean Dipole (IOD) phases are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD phases.
The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between SST anomalies in two regions of the tropical Indian Ocean (see map):
IOD regions:
- IOD west: 50°E to 70°E and 10°S to 10°N
- IOD east: 90°E to 110°E and 10°S to 0°S
A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.
For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.
- Details about:
- IOD
- IOD phases
The Southern Annular Mode index
The Southern Annular Mode, or 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.
- Details about:
- About SAM
About the data
Data periods
Daily datasets have a value for every day in their record. Similarly, weekly and monthly (30 day) data sets have values for every week or month (30 days), respectively, in their record.
Sea surface temperature 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° latitude by 0.25° 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° 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).
- BoM GAMSSA SST analysis: Beggs et al. (2011) and Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Early SST data
Before the satellite era, the primary source of SST data was observations made by ships passing through the region. The frequency of these observations was too low to produce a useful weekly dataset, so it is shorter than the monthly dataset. IOD and ENSO event identification using early SST data has limited accuracy, particularly for the Indian Ocean.
SOI data
Data source: Bureau SOI data
The SOI data includes a long history of monthly pressure readings from Darwin and Tahiti that have been digitised for electronic use. Old daily pressure readings have not yet been digitised, so a shorter dataset is available.
- See also: Links open in new window
- SST timeseries graphs
- Sea surface temperature maps
- Map of NINO and IOD regions
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.
About these graphs
Climate indices
An index is a measure (often a numerical value) that can be representative of a particular pattern or state of a system. Climatologists monitor several indices, some ocean-based and some atmospheric, to provide a quick indication of the state of certain climate variables and climate indicators.
El Niño–Southern Oscillation indices
El Niño and La Niña (collectively referred to as the El Niño–Southern Oscillation or ENSO) are characterised by changes in the equatorial Pacific Ocean. During El Niño, sea surface temperatures (SST) in the central and eastern Pacific Ocean become warmer than average, while during La Niña these SSTs become cooler than average.
Niño indices regions
To monitor the Pacific Ocean for signs of El Niño or La Niña, climatologists use several SST indices. These indices measure the difference between the current sea surface temperature and its long-term (1991–2020) average in several regions located along the equatorial Pacific. The difference is referred to as an anomaly. These regions are labelled Niño1, Niño2, Niño3, Niño3.4 and Niño4 and are used by meteorological agencies around the world.
Relative Niño indices
Traditional Niño index values were used at the Bureau of Meteorology until September 2025. From September 2025, the Bureau uses Relative Niño indices, which measure sea surface temperature anomalies in the tropical Pacific Ocean in the Niño regions, but calculated relative to the global tropical region temperature anomaly. This is to relate the indices more closely to the localised processes associated with ENSO, rather than larger-scale tropical SST features such as global warming.
Example: The Relative Niño3.4 index calculation:
Relative Niño3.4 = S x [(Niño3.4obs – Niño3.4clim) – (Tropical Meanobs – Tropical Meanclim)]
Where Niño3.4obs and Tropical Meanobs are the SST averages over the Niño3.4 region and the 20°S to 20°N tropical mean SST, respectively, while Niño3.4clim and Tropical Meanclim are the climatological values for the appropriate day/month depending on the dataset. S is a scaling factor applied so the variance of the relative Niño index matches that of the traditional index.
For the analysis of ENSO status, Relative Niño indices are used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). Bureau climatologists cite sustained monthly Relative Niño3 or Niño3.4 index values above +0.8 °C as typical of El Niño conditions, with values of below −0.8 °C as typical of La Niña. These values are approximately one standard deviation from the long-term mean (e.g., around 70% of monthly Niño3.4 values, lie between −0.8 °C and +0.8 °C).
The Niño regions in the Pacific Ocean, are used to monitor ENSO, with Niño3 and Niño3.4 typically used to identify El Niño and La Niña.
Niño regions cover the following areas:
- Niño1 (far eastern equatorial Pacific): 5–10°S, 90–80°W
- Niño2 (far eastern equatorial Pacific): 0–5°S, 90–80°W
- Niño3 (eastern equatorial Pacific): 5°N–5°S, 150–90°W
- Niño3.4 (central equatorial Pacific): 5°N–5°S, 170–120°W
- Niño4 (western equatorial Pacific): 5°N–5°S, 160°E–150°W
For monitoring of ENSO phases, the value of the Niño indices are often used in conjunction with other data, e.g., sub-surface ocean temperatures, cloudiness, winds, and the Southern Oscillation Index (SOI). The Bureau cites sustained monthly Niño3 or Niño3.4 values above +0.8 °C as being associated with El Niño, and values below −0.8 °C being associated with La Niña. These values are approximately one standard deviation from the long-term mean (i.e., around 70% of monthly Niño3 values in the historical record, for example, lie between −0.8 °C and +0.8 °C).
Details about: El Niño and La Niña
Southern Oscillation Index (SOI)
The Southern Oscillation Index, or SOI, gives an indication of the state and intensity of ENSO, from an atmospheric perspective. The SOI is calculated using the pressure differences between Tahiti and Darwin.
Sustained negative values of the SOI below −7 often indicate El Niño is active while sustained positive values above +7 are typical of a La Niña.
Technical details
There are a few different methods for calculating the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. The base period used in the SOI calculation is 60 years (1933–1992).
Calculation
Pdiff − Pdiffav
SOI = 10 x -------------------,
SD(Pdiff)
where:
Pdiff = (average Tahiti MSLP for the period) − (average Darwin MSLP for the period),
Pdiffav = long term average of Pdiff for the period in question, and
SD(Pdiff) = long term standard deviation of Pdiff for the period in question.
The multiplication by 10 is a convention to make the final value more readable. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The SOI is usually computed on a monthly basis, with values over longer periods such a three-month average being sometimes used. Daily values can also be averaged over a longer period to form a multi-day average. Single-day or weekly values of the SOI are not so useful for information on the current state of the climate, as these values are dominated by the effects of short-term weather variability, and accordingly the Bureau of Meteorology does not issue them. In particular, single-day values can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.
Details about: SOI
The Indian Ocean Dipole index
Indian Ocean Dipole (IOD) phases are driven by changes in the tropical Indian Ocean. Sustained changes in the difference between normal sea surface temperatures in the tropical western and eastern Indian Ocean are what characterise IOD phases.
The IOD is commonly measured by an index (sometimes referred to as the Dipole Mode Index, or DMI) that is the difference between SST anomalies in two regions of the tropical Indian Ocean (see map):
IOD regions:
- IOD west: 50°E to 70°E and 10°S to 10°N
- IOD east: 90°E to 110°E and 10°S to 0°S
A positive IOD period is characterised by cooler than average water in the tropical eastern Indian Ocean and warmer than average water in the tropical western Indian Ocean. Conversely, a negative IOD period is characterised by warmer than average water in the tropical eastern Indian Ocean and cooler than average water in the tropical western Indian Ocean.
For monitoring the IOD, Australian climatologists consider sustained values above +0.4 °C as typical of a positive IOD, and values below −0.4 °C as typical of a negative IOD.
Details about: Indian Ocean Dipole
The Southern Annular Mode index
The Southern Annular Mode, or 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 reasearch paper: Southern annular mode impacts on global ocean surface waves.
Details about: Southern Annular Mode
About the data
Data periods
Daily datasets have a value for every day in their record. Similarly, weekly and monthly (30 day) data sets have values for every week or month (30 days), respectively, in their record.
Sea surface temperature 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° latitude by 0.25° 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° 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).
- BoM GAMSSA SST analysis: Beggs et al. (2011) and Beggs et al. (2020)
- Climatology: 1991–2020 European Space Agency (ESA) SST Climate Change Initiative (CCI) Climatology product version 3.0
Early SST data
Before the satellite era (which began in the early 1980s), the primary source of SST data was observations made by ships passing through the region. The frequency of these observations was too low to produce a useful weekly dataset, so it is shorter than the monthly dataset. IOD and ENSO event identification using early SST data has limited accuracy, particularly for the Indian Ocean.
SOI data
Data source: The Bureau maintains a SOI database.
The SOI data includes a long history of monthly pressure readings from Darwin and Tahiti that have been digitised for electronic use. Old daily pressure readings have not yet been digitised, so a shorter dataset is available.
About Pacific, Indian and Southern ocean indices
History
Unless otherwise noted, all maps, graphs and diagrams in this page are licensed under the Creative Commons Attribution 4.0 International Licence
