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Marine heatwaves

Where the sea surface was warmer or cooler than usual on 25 September 2026. A temperature anomaly from NOAA Coral Reef Watch, not a classified heatwave category.

NOAA CRW · 5 km sea-surface temperature anomaly

Where the sea surface was warmer or cooler than usual on 25 September 2026. A temperature anomaly from NOAA Coral Reef Watch, not a classified heatwave category.
Map: Fix Planet from NOAA Coral Reef Watch 5 km sea-surface temperature anomaly, 25 September 2026. The number is degrees Celsius. Boundaries: Natural Earth.

What it is

The map is the NOAA Coral Reef Watch daily 5 km sea-surface temperature anomaly for 25 September 2026, in degrees Celsius. A marine heatwave is a longer event: a region that stays much warmer than its seasonal norm. Coral Reef Watch also publishes heat-stress products, and the NOAA Physical Sciences Laboratory explains category definitions. Those category maps are not this plate. marineheatwaves.org keeps a separate tracker.

Why it matters

Average sea-surface temperature describes the usual state of the ocean. This map shows where that day was unusually warm or cool. Sustained warmth is what stresses coral reefs. A single anomaly day is the field those heatwave definitions start from.

How to read it

The colour is degrees Celsius above or below the usual temperature for that place. It is one day, not a count of heatwave days. It is also different from ocean heat content, which measures heat stored through the depth of the water. The Physical Sciences Laboratory and marineheatwaves.org pages define the event.

Sources

Open source map →