Marine heatwave Bulletin
Forecasts for 6 December 2025​

Key takeaways

  • Mediterranean Sea – marine heatwave in the eastern part of the basin is decreasing in extent and remains stable in intensity.
  • Southern Ocean – the marine heatwave at 60°S in the Southern Ocean is intensifying.
  • Tropical Pacific – event off the northern coast of Chile remains stable in extent but is increasing in intensity. Events between Papua New Guinea and Newzeland and near 100°W are increasing in intensity.
Waves

Marine heatwave categories

European Zone

Marin heatwave categories forecast for 6 December, 2025. European Zone. Credit: Mercator Ocean International

Mediterranean Sea

The marine heatwave in the eastern part of the basin is decreasing in extent and remains stable in intensity, with only a few scattered areas in the moderate and strong categories.

Global Ocean

Marin heatwave categories forecast for 6 December, 2025. European Zone. Credit: Mercator Ocean International

Tropical Atlantic

The marine heatwave affecting the basin is decreasing in extent while remaining in the moderate and strong categories. The marine heatwave west of Liberia is decreasing in extent, and only one scattered area remains in the moderate and strong categories.

Southern Ocean

The marine heatwave at 60°S in the Southern Ocean is intensifying, shifting from moderate and strong categories to strong, severe, and locally extreme.

North Pacific

The area covered by marine heatwaves throughout the basin is decreasing. Their intensity remains stable, ranging from moderate to locally strong.

Tropical Pacific

The marine heatwave located between Papua New Guinea and New Zealand is decreasing in intensity. The marine heatwave in the eastern part of the basin near 100°W is decreasing in both intensity and extent. The marine heatwave off the northern coast of Chile remains stable in extent but is increasing in intensity.

Indian Ocean

The marine heatwave west of Sumatra is increasing in intensity, moving overall into the moderate and strong categories. The extent of the marine heatwave east of Madagascar persists, but its intensity is increasing and now falls within the moderate and strong categories.

Weekly temperature anomalies

 


Weekly sea surface temperature anomaly map for the week of 30 November to 6 December 2025. GLO12 forecast. Source: Mercator Ocean International

 

 

Tropical Atlantic 0°C to 2°C
Southern Ocean -1°C to 2°C
North Pacific -2°C to > 3°C
Tropical Pacific -2°C to 3°C
 Indian Ocean -3°C to 2°C
Mediterranean Sea 0°C to 2.5°C

Forecasts for 6 December 2025

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NOTES

Datasets and products: Global Ocean Physics Analysis and Forecast (sea surface temperature) E.U. Copernicus Marine Service/ Mercator Ocean International. https://doi.org/10.48670/moi-00016