Mercator Ocean International
Ocean Temperature Bulletin

Ocean Temperature Bulletin
June 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

  • June 2026 was the warmest June on record for the global ocean ( 60°S-60°N) with a mean Sea Surface Temperature (SST) of 20.92 ± 0.10°C, supassing the previous record in 2024.
  • Last month, 81% of the ocean showed above-average mean SST and 21% supassed 1°C above average.
  • In the Mediterranean Sea, June 2026 ranked also the warmest June on record with a mean SST of 24.07 ± 0.49°C, with the previous recordsbeing set in 2023 and 2025.
  • Almost the entire Mediterranean Sea (95%) registered above average SST with higher values exceeding 2°C in the western part of the basin.
  • The Tropical Pacific (between 30°S and 30°N) experienced a monthly mean temperature of 27.26 °C, surpassing previous record levels in 2023 (26.90 °C) and SST anomalies exceeded 2°C above the average in the eastern part – an indication of the transition into an El Niño phase.
  • Globally, June 2026 ranked among the three most extreme Junes on record regarding marine heatwave activity, whereas in the Mediterranean Sea, marine heatwaves were the most intense for a June month since 1993.

sea Surface Temperature

 

Figure 1:  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.

  • June 2026, at global level (between 60°S and 60°N), was the warmest June on record, with a mean Sea Surface Temperature (SST) of 20.92 ± 0.10°C , surpassing the previous record set in 2024 (20.90±0.07°C).
  • Regionally, for the Mediterranean Sea, June 2026 was also the warmest June on record, with a mean SST of 24.07 ± 0.49°C , noticeably warmer than previous records of June 2003 (23.96 ± 0.44 °C) and 2025 (23.95± 0.40°C). For the North Atlantic (between 0°N and 60°N), June 2026 was the 13th  warmest June month with a mean SST of 22.71 ± 0.23 °C, the record being June 2024 (23.46 ± 0.13°C).
  • The Tropical Pacific (between 30°S and 30°N) experienced a monthly mean temperature of 27.26 °C, surpassing 2023 levels (26.90 °C).

 

SEA SURFACE TEMPERATURE ANOMALIES

June 2026 Mean SST Anomaly 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 June 2026, 81% of the global ocean (between 60°S and 60°N) show above average mean SSTs, and 21% of the global ocean is above average by at least 1°C (Figure 2).

  • Most of the Mediterranean Sea (95%) showed above-average SSTs, with stronger SSTs in the western part, exceeding 2°C.
  • The North Pacific Ocean showed predominantly warmer than average SSTs, spanning the entire width of the basin and reaching 3°C above average in the Kuroshio region and its extension as well as on the eastern part between Hawaii and Mexico . In the South Pacific, strong SSTs, reaching 3°C above average were observed off the Peru coast. In the Tropical Pacific, SST are above average for the entire width of the basin, exceeding 2°C above the average in the eastern part. This marks the transition to an El Niño phase of ENSO
  • The North Atlantic, A broad band of above-average SSTs stretches across the basin, from the Caribbean to northern Europe, where the anomalies exceed 2°C. Mid-latitudes showed below-average SSTs, between the Canadian coast and 20°W. The South Atlantic showed below average temperature on the eastern part along the African coast.
  • In the Indian Ocean, above-average sea surface temperatures (SST) are being observed to the east of Madagascar, in the Arabian Sea and to the west of Indonesia, where they are locally approaching 2°C above average.

 

 

 

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

 

 

The ranking of average monthly SSTs is monitored so to contextualise the current situation relative to previous Junes. This ranking is based on June monthly SST averages from 1993 to 2026. Here, we look at the ranking of June 2026 among all June months since 1993.

  • Around 12% of the global ocean (between 60°S and 60°N) ranked as the warmest June month on record, with regions in the equatorial Pacific, Southern Ocean and surrounding western Europe most affected.
  • Regions such as the south-western Pacific (around New Zealand) and the north-eastern Pacific are also affected by large areas where June was the warmest on record.
  • 14% of the Mediterranean Sea ranked as the warmest June month on record and 76% of its area was among the four warmest Junes on record.
    In the equatorial Pacific (30°S and 30°N) June 2026 was the warmest June for 24% of the region covering a large region from the north-eastern equatorial region that extends to the west the full width of the basin.

Ongoing Marine Heatwaves

The duration of ongoing MHWs is monitored because prolonged events induce important stress on marine ecosystems (see section What are Marine Heatwaves?). Here we look at the MHWs present on 30th June 2026 and monitor their duration. For each region affected, we show in colour the month when the MHW first appeared (month of onset): for instance, ocean pixels in red correspond to MHWs that developed during June 2026 and that are therefore less than one month old; in orange MHWs between 1 and 2 months old, and so on…

 

Month of onset for the ongoing MHWs on the 30th of June 2026. The colours indicate the month during which the MHW started. For instance, ocean pixels in red correspond to an MHW that developed during Junel 2026 and are less than one month old, in orange MHW between 1 and 2 months old, etc.
  • On the 30th of June, 33% of the global ocean (between 60°S and 60°N) was affected by MHWs.
  • The majority of these MHWs developed recently, with 20% of the global Ocean (between 60°S and 60°N) affected by MHWs less than 1 month old and 11% by events between 1- and 2-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 in the south of California. 3-month-old MHWs can also be found in the South Pacific around 120°W. In the South Pacific, around New Zealand, MHWs reached 3 or 4 months
  • In the Southern Ocean, between 60°E and 90°E, persistent MHWs are also present with duration reaching 3 to 4 months.

Total Surface Marine Heatwaves

MHWs are classified into four categories: Moderate, Strong, Severe, and Extreme. We monitor daily the surface area affected by MHWs and show the proportion of the global ocean (between 60°S and 60°N) exposed to MHWs – both overall and for each category – over the past year (since June 2025). We focus on the evolution over the past June 2026 (denoted in grey). ​

  • In June 2026, the total surface area of MHW (black line) increased from 29% to 34% of the global ocean (between 60°S and 60°N. The majority of MHWs events were of moderate categories (around 23% to 25% of the global ocean) with strong category events increasing steadily across the month to reach around 6% of the global ocean. For comparison, the total surface occupied by MHWs at the end of June 2025 was notably lower (~19% by the end of the month).
Surface occupied by MHWs in the Mediterranean Sea between July 2025 and June 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 June 2026.

 

Mediterranean Sea

  • For the Mediterranean Sea, the total area covered by MHWs increased during June 2026, from 52% to 67%, with a drop at 33% in the middle of the month. These MHWs were mainly of moderate and strong category, with a significant increase in extent for the strong categories in the second half of the month (36%).
Surface occupied by MHWs in the Mediterranean Sea between July 2025 and June 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 June 2026.

 

North Atlantic (between 0°N and 60°N)

  • For the North Atlantic (between 0°N and 60°N), the total surface area of MHW increased significantly across the month to reach 26% of the area by the end of June 2026, to reach highest levels since a year. These events are predominantly of moderate category, with an increase of strong category towards the end of the month (~5%).

 

Surface occupied by MHWs in the North Atlantic (between 0°N and 60°N) between July 2025 and June 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 June 2026.

 

Total Number Marine Heatwaves

June 2026 MHW days of strong and higher category. Number of days during which a MHW of category strong, severe or extreme occurred in June 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.

We monitor the number of MHW days to highlight regions most impacted by MHWs – these can be a series of short events or one long one. Longer and more frequent MHWs increase heat stress on marine ecosystems, especially intense MHWs (i.e., MHW of strong or higher category). Here we look at the total number of days where a MHW of category strong or higher occurred during June 2026. For instance, ocean regions in light green correspond to areas where a total of 10 to 15 days of strong or higher MHW were observed during the month of June of 2026.

 

Year by year evolution of the surface impacted by strong and higher MHW during months of June. 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.
  • 21% of the surface of the ocean was impacted by strong-or-higher MHW conditions for at least 1 day during June 2026. This is the 2nd widest extent of the last 34 years, after 2024 (24%). 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 (Figure 7). In the south of New Zealand, MHWs also persisted the entire month.
  • Regionally, 16% of the North Atlantic (between 0°N and 60°N) was impacted by strong, or higher, MHW conditions for at least 1 day. This corresponds to the 6th largest extent of the last 34 years for a June month. The record was set in June 2023, with 56% of the area impacted by strong, or higher, MHW conditions for at least 1 day.
  • For the Mediterranean Sea, 70% of the basin was affected by strong-or-higher MHW conditions for at least 1 day, which is a record for the month of June, ahead of June 2025 with 64%

Statistics

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 (top), for the Mediterranean Sea (centre and the North Atlantic Ocean (bottom). June 2026 is highlighted with a blue edge.

 

We calculate average characteristics for the MHWs that occurred in June 2026 (duration, intensity, surface occupied and activity) for the global ocean, the North Atlantic, and the Mediterranean Sea. This allows us to obtain a MHW profile for June 2026 that can be compared to those of June months from previous years (since 1993) in a bubble plot (see Figure 8). Each bubble corresponds to June of a given year, its position on the horizontal axis indicates the average MHW duration, and on the vertical axis the average intensity, i.e. the more a bubble is in the top right corner the longer and intense the mean MHW profile is. In addition, the size of each bubble indicates the total surface area impacted by a MHW during the month, and the colour represents the MHW activity – the cumulation of the extra temperature above average in space and time.

 

  • On a global scale, June 2026 was one of the three most extreme Junes in terms of MHW intensity, duration, surface and activity, together with 2023 and 2024.
  • In the Mediterranean Sea, June 2026 was the most extreme June in terms of MHW intensity, and the 5th  in terms of MHW mean duration, behind 2018, 2003, 2024 and 2025.
  • In the North Atlantic, June 2026 stands within the 10 most extreme June month in terms of MHW from the last 34 years.

 

About the Bulletin

Marine heatwaves (MHW) are extreme rises in ocean temperature for an extended period of time. They can occur at different locations in the ocean, and their magnitude and frequency have increased over the last couple of decades, with harmful impacts on ecosystems, and human activities. According to the latest report released by the Intergovernmental Panel on Climate Change (IPCC AR6 SYR), it is found with high confidence that in the near-term at 1.5°C global warming, the increasing frequency of marine heatwaves will increase risks of biodiversity loss in the oceans, including from mass mortality events (IPCC AR6 SYR).

How are Marine Heatwaves calculated?

A MHW is an episode during which the ocean temperature is abnormally warm for at least 5 consecutive days.

Adapted from Hobday et al., 2018.

For any location in the ocean, the normal temperatures are defined for every day of the year using a climatological period (here 1993–2022). A MHW is identified when the measured daily temperature is within the top 10% of the highest recorded values for that day (i.e., above the 90th percentile, see diagram above), and with this condition persisting for at least five consecutive days.

The intensity of the heatwave on any given day is measured as the number of degrees above the climatological average (represented by the bold black line) indicated by the blue arrow. We can either calculate the cumulative intensity over the entire heatwave, the mean intensity or record the maximum intensity.

MHWs are classified based on their intensity level. To do this, the intensity is compared to the difference between the climatological value and the 90th percentile value. A MHW intensity between 1 and 2 times this difference corresponds to a heatwave of moderate category; between 2 and 3 times, to a strong category; between 3 and 4 times, to a severe category; and a difference greater than 4 times corresponds to an extreme category.

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 June  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. E.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 March (1993 to 2023), 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.