Mercator Ocean International
Ocean Temperature Bulletin

Ocean Temperature Bulletin
August 2026

Mercator Ocean International (MOi) oceanographers examine marine heatwaves across the global ocean. They analyse a variety of datasets from observation analyses
(satellite sea surface temperature maps) to model analyses
(assimilating satellite and in situ observations) and model forecasts.¹

All images in this article can be used freely and should be credited with the following information :
Image source: European Union, Copernicus Marine Service Data 2025 © Mercator Ocean .

Key takeaway

  • August 2026 was the warmest August since 1993 for the global ocean, with a mean sea surface temperature (SST) of 21.11 ± 0.08°C, surpassing the previous record set in 2023.
  • The warmest regions were detected in the tropical Pacific, subtropical North Atlantic and surrounding western Europe. Regions such as the south-western Pacific (around New Zealand) and the southern part of the Bering Sea is also characterised by vast areas where August was the hottest on record.
  • 45% of the Mediterranean Sea ranked as the warmest August month on record and 70% of its area was among the four warmest Augusts on record. 

sea Surface Temperature

 

 

Daily sea surface temperatures averaged for the global ocean (left), the Mediterranean Sea (middle) and the North Atlantic Ocean (right) between 1991-2020 using ESA’s Climate Change Initiative (grey shades), and between 2021-2026 (coloured shades) using Mercator Ocean International’s GLO12 analysis and forecast.

 

  • August 2026, at global level (between 60°S and 60°N), was the warmest August on record, with a mean Sea Surface Temperature (SST) of 21.11 ± 0.08°C , significantly exceeding the previous record set in 2023 (21.01±0.06°C). 
  • Regionally, for the Mediterranean Sea, August 2026 was also the warmest August on record, with a mean SST of 28.27 ± 0.19°C , warmer than previous record of August 2024 (28.11 ± 0.08 °C).
  • For the North Atlantic (between 0°N and 60°N), August 2026 was the 3rd warmest August month with a mean SST of 25.24 ± 0.16°C, behind August 2024 (25.37 ± 0.06°C) and  2023 (25.51 ± 0.10°C).  

Sea surface temperature anomalies

 

Mean sea surface temperature anomaly in August 2026 relative to a 30-year climatology (1993-2022), calculated using daily data from Mercator Ocean International’s GLO12 analysis and forecasting system for 2026 and from the GLORYS12 reanalysis for the climatological mean.

 

In August 2026, 77% of the global ocean (between 60°S and 60°N) show above average mean SSTs, and 26% of the global ocean is above average by at least 1°C (Figure 2).

  • Most of the Mediterranean Sea (90%) showed above-average SSTs, with stronger SSTs in the western part, reaching more than 3°C along the French coast. 69% of the Mediterranean Sea is above average by at least 1°C
  • The North Pacific Ocean has seen sea surface temperatures (SSTs) that were mostly above average, covering a band in the Sea of Japan and in the central North Pacific, reaching or even exceeding 3 °C above average. In the eastern region between Hawaii and Mexico, SSTs reached between 2 and 3°C above average. In the South Pacific, SSTs are between 1 and 2°C above average around New Zealand and may locally reach 2.5 °C in south-eastern Australia. Along the Chilean coast, SSTs reach or even exceed 3 °C above average.
  • In the Equatorial Pacific (cf supplements), the entire band between 180°W and the coast of South America is characterised by high SSTs, with large areas exceeding 3°C above average. Near the coasts, these above-average SSTs extend from Central America to the Peruvian coast, with values exceeding 4°C and potentially rising above 5°C. This development marks the intensification of the El Niño.
  • 87% of the North Atlantic show above average mean SST, with 23% above average by at least 1°C. A broad band of above-average SSTs stretches across the basin, from the Caribbean to western and northern Europe, where the anomalies exceed 2°C and locally reached 3°C, particularly in the Bay of Biscay and the North Sea . Mid-latitudes showed below-average SSTs, between the Canadian coast and 30°W (“cold blob” region).
  • The South Atlantic showed patchy above-average SSTs across the entire width of the basin, between 30°S and 50°S.
  • In the Indian Ocean, above-average sea surface temperatures (SSTs) are being observed to the east and north of Madagascar, and in the south- west of Indonesia, where they are locally close to 2 °C above average.

 

Ranking August 2026

 

Ranking of monthly August 2026 SSTs against previous August months of the historical period (since 1993). 

 

  • Around 18% of the global ocean (between 60°S and 60°N) ranked as the warmest August month on record, with regions in the tropical Pacific, subtropical North Atlantic and surrounding western Europe most affected.
  • Regions such as the south-western Pacific (around New Zealand) and the southern part of the Bering Sea is also characterised by vast areas where August was the hottest on record.
  • 43% of the Mediterranean Sea ranked as the warmest August month on record and 70% of its area was among the four warmest Augusts on record. 

 

Ongoing Marine Heatwaves

Ongoing marine heatwave events on 31 August 2026

Month of onset for the ongoing MHWs on the 31st of August 2026. The colours indicate the month during which the MHW started. For instance, ocean pixels in red correspond to an MHW that developed during August 2026 and are less than one month old, in orange MHW between 1 and 2 months old, etc. 

  • On the 31st of August, 38% of the global ocean (between 60°S and 60°N) was affected by MHWs.
  • The majority of these MHWs developed recently, with 19% of the global Ocean (between 60°S and 60°N) affected by MHWs less than 1 month old and 16% by events between 1 and 3 month old.
  • Widespread and persistent MHWs are found in the central Pacific, spanning the entire width of the basin, with the oldest MHW developed in December-January in the south of California.
  • In the Southern Ocean, between 60°E and 90°E, persistent MHWs are also being observed, which can last for up to 4 to 5 months. In very localised areas, some MHWs have persisted since January or December.

Total Surface Marine Heatwaves

Global Ocean (60°S-60°N)

 

Maximum surface (%) occupied by MHW by each category (moderate, strong, severe and extreme) since 1993.

  • In August 2026, the total surface area of MHW (black line) fluctuated between 35% and 39% of the global ocean (between 60°S and 60°N. The majority of MHWs events were of moderate categories (around 23-24% of the global ocean) and strong category that reached around 10-12% of the global ocean. For comparison, the total surface occupied by MHWs at the end of August 2025 was notably lower (~20% by the end of the month). 

Surface occupied by MHWs in the global ocean (between 60°S and 60°N) between September 2025 and August 2026 based on daily monitoring. The black solid line represents the total surface of MHW, while the coloured lines represent the surface of each MHW category. The grey background highlights the month of August 2026.

Mediterranean Sea

 

  • In the Mediterranean Sea, the total area covered by MHWs increased during August 2026, going from 59% to 63%, with peaks reaching 70% during the month. Towards the end of the month, the trend was downwards, decreasing from 70% to 63% over the last five days. These MHWs were mainly of moderate category early August. Then, strong categories became more widespread than moderate ones. By the end of the month, the areas affected by severe categories had increased significantly, exceeding those affected by moderate categories (19% compared with 15% on 31 August). For comparison, the total surface occupied by MHWs at the end of August 2025 was notably lower (11%), with mainly moderate category. 

Surface occupied by MHWs in the Mediterranean Sea between August 2025 and August 2026 based on daily monitoring. The black solid line represents the total surface of MHW, while the coloured lines represent the surface of each MHW category. The grey background highlights the month of August 2026.

North Atlantic  (0°N and 60°N)

Surface occupied by MHWs in the North Atlantic (between 0°N and 60°N) between August 2025 and August 2026 based on daily monitoring. The black solid line represents the total surface of MHW, while the coloured lines represent the surface of each MHW category. The grey background highlights the month of August 2026.

  • In the North Atlantic region, the total surface area of MHW increased significantly during the month, from 31% to 40% at the end of August. These events are predominantly of moderate (23%-33%) and strong (6%-11%) categories, with a peak of severe category at the middle of the month, reaching close to 4% of the total surface area. 

 

Total Number Marine Heatwaves

Intense marine heatwaves are events categorized as strong or higher

 

August 2026 MHW days of strong and higher category. Number of days during which a MHW of category strong, severe or extreme occurred in August 2026. Blank areas mean that no MHW of strong or higher category happened during the month. Blue shaded areas in the polar regions represent the sea ice maximum from the climatological period (1993-2022). Monitoring SST extremes with the MHW categorization approach as used here is not best suited for such regions.  

 

Year by year evolution of the surface impacted by strong and higher MHW during months of August. The size of the bar represents the proportion of the global ocean (between 60°S and 60°N) exposed to a strong or higher MHW during the month. As indicated by the colours, the proportion exposed to such MHWs is categorized according to the number of days impacted during the month.  

 

  • 29% of the surface of the ocean was impacted by strong-or-higher MHW conditions for at least 1 day during August 2026. This is the 1st widest extent of the last 34 years, far exceeding the previous record set in 2024 (25 %). The central Pacific and the Southern Ocean, between 40°E and 80°E are the most affected, with areas where MHWs persisted the entire month.
  • In the North Atlantic (between 0°N and 60°N), 38% was impacted by strong, or higher, MHW conditions for at least 1 day. This corresponds to the 3rd largest extent of the last 34 years for a August month, behind 2024 (48%) and 2023 (61%). Western Europe and the band between 25°N and 35°N are the regions that have been affected by strong MHWs or higher for the longest period of time
  • For the Mediterranean Sea, 75% of the basin was affected by strong-or-higher MHW conditions for at least 1 day, which is a record for the month of August, far ahead of August 2024 with 66%
  • For the Equatorial Pacific, 44% of the bassin was affected by strong-or-higher MHW conditions for at least 1 day, which is the 1st widest extent, far ahead of 2015 (26%).

 

 

Year by year evolution of the surface impacted by strong and higher MHW during months of August. The size of the bar represents the proportion of the Equatorial Pacific (between 30°S and 30°N) exposed to a strong or higher MHW during the month. As indicated by the colours, the proportion exposed to such MHWs is categorized according to the number of days impacted during the month.  

Statistics

Marine heatwave characteristics

  • On a global scale, August 2026 was the most extreme August in terms of MHW, well ahead of 2023 and 1997. 
  • In the Mediterranean Sea, August 2026 was the most extreme August far ahead 2024. 
  • In the North Atlantic, August 2026 was the 3rd most extreme August month in terms of MHW from the last 34 years, behind 2024 and 2023.

MHW Characteristics for Mat months from 1993 to 2026. Duration, intensity, extent and activity averaged for each March month between 1993 and 2026 for the global ocean (left), for the Mediterranean Sea (centre and the North Atlantic Ocean (right). August 2026 is highlighted with a blue edge.

About the Bulletin

Mercator Ocean International publishes a monthly sea surface temperature bulletin reporting on mean temperature and marine heatwave conditions for the month just passed. It includes:

  • Regions where MHWs are present and the time these events started,
  • Timeseries showing the total surface occupied by MHWs globally and for the European region,
  • The total number of days of exposure to MHW during the month (including only strong and higher intensity categories).

Data sets and products

Sea Surface Temperature

The results are obtained using the Copernicus Marine Service global analysis and forecasting system together with observation-based products.

  • GLOBAL_ANALYSISFORECAST_PHY_001_024 Global Ocean Physics Analysis and Forecast sea surface temperature. U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
  • ESA SST CCI reprocessed sea surface temperature analyses. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00169
  • NOAA OI SST V2 High Resolution Dataset data provided by the NOAA PSL, Boulder, Colorado, USA, from their website at https://psl.noaa.gov, Huang, B., C. Liu, V. Banzon, E. Freeman, G. Graham, B. Hankins, T. Smith, and H.-M. Zhang, 2021: Improvements of the Daily Optimum Interpolation Sea Surface Temperature (DOISST) Version 2.1, Journal of Climate, 34, 2923-2939. doi: 10.1175/JCLI-D-20-0166.1
  • Global Ocean OSTIA Sea Surface Temperature and Sea Ice Analysis. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00165
  • ODYSSEA Global Sea Surface Temperature Gridded Level 4 Daily Multi-Sensor Observations. E.U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016

Notes: The global analysis system was used to study the ocean surface temperature from 2021 and 2025. To study surface temperature for previous years (1991 to 2020), it was used the ESA CCI data. The other observation-based sea surface temperature products (OSTIA, OI SST and Odyssea) were used for calculating monthly mean and uncertainty values for August 2026.

 Marine Heatwaves

The results are obtained using the Copernicus Marine Service global systems including the analysis and forecasting system together with the reanalysis product.

  • GLOBAL_ANALYSISFORECAST_PHY_001_024 Global Ocean Physics Analysis and Forecast sea surface temperature. U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00016
  • GLOBAL_MULTIYEAR_PHY_001_030 Global Ocean Physics Reanalysis sea surface temperature. U. Copernicus Marine Service Information (CMEMS). Marine Data Store (MDS). DOI: https://doi.org/10.48670/moi-00021

Notes: The global analysis system was used to study MHWs for 2024 and 2025. To study MHWs for previous August months (1993 to 2025), it was used the reanalysis system. The reanalysis product was used for generating a daily climatology using the 30-year period from 1993 to 2022