Sea Surface Temperature (SST) maps

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:

• 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

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.