The marine heatwave bulletin provides forecasts and analysis of marine heatwave events across the globe and throughout the year. Used datasets include observations (satellite sea surface temperature maps) and numerical model analyses (assimilating satellite and in situ observations) to derive marine heatwave forecasts for a 10-day period. [1] This week’s forecasts were produced using as a comparison the marine heatwave situation on 25/02/2025.
Forecasts for 8 March
Indian Ocean
The marine heatwave to the east of Madagascar and in the Arabian Sea decreases in intensity and in extent with moderate to strong categories. In the North of Australia, the marine heatwave increases in intensity and in extent with moderate to strong categories.
Tropical Pacific Ocean
The marine heatwave present in the west of the basin and affecting Indonesia, the Philippines and Papua New Guinea has seen its extent and intensity greatly decrease, with mostly moderate categories and locally strong. To 120° Weast, a marine heatwave appears with moderate to strong categories and locally sever.
South Pacific Ocean
At the center of the basin between 150°W and 120°W, the marine heatwave increases with moderate to strong and locally sever categories. The marine heatwave off the Chilean coast is increases in intensity with the strong category extent.
Tropical Atlantic Ocean
In the Carribean Sea, the marine heatwave increases in intensity with mostly strong category. In the basin middle the marine heatwave decreases in extent and increases in intensity with strong to sever categories.
South Atlantic Ocean
Off the Brazilian coast the marine heatwave increases in extent and in intensity with moderate to strong and locally sever categories.
European Zone
Weekly Temperature Anomalies
02/03/2025-08/03/2025
Mean sea surface temperature anomalies in each global ocean region for the week 2 to 8 March, 2025.
| Indian Ocean | 0°C to 1.5°C |
| Tropical Atlantic Ocean | 0°C to 2°C |
| South Atlantic Ocean | 0°C à 3°C |
| Tropical Pacific Ocean | -1.5°C to 2.5°C |
| South Pacific Ocean | -0.5°C to 3°C |
| South Atlantic Ocean | 0°C à 3°C |
Access the Daily Global Physical Bulletin for a 9-day forecast here.
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What are marine heatwaves?
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.[2]
How are marine heatwaves calculated?
A marine heatwave 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 1993–2016). A heatwave 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), 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 or record the maximum intensity.
Heatwaves 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.
Notes
[1] Analysis of datasets: SST OSTIA (Copernicus Marine Service), OISST (NOAA), GLO12 (Copernicus Marine Service / Mercator Ocean International), PSY4 (Copernicus Marine Service / Mercator Ocean International), and GLO12 et PSY4 forecasts.
[2] IPCC AR6 SYR chapter 4.3 https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_LongerReport.pdf