As the UK enters its third heatwave of the year with a prolonged spell of hot and dry weather, the Met Office is warning that a long-lasting UK marine heatwave is likely to reach extreme levels this week.
Surface waters in Northwest European seas are currently experiencing moderate to severe marine heatwave conditions, with widespread areas of “strong” Category 2 conditions and some locations reaching “severe” Category 3.
Across UK waters, widespread Category 2 marine heatwave conditions are present around much of the English and Welsh coastlines, the English Channel, and the central and southern North Sea.
This means that waters have reached temperatures usually expected in August and are on average 2°C warmer than usual, locally reaching up to 5°C warmer on offshore parts of the Welsh and English coasts.
The provisional UK June temperature record was exceeded on three consecutive days in June. Typically lagging inland weather by around 3-5 days, sea-surface temperatures have responded quickly, with the Bay of Biscay reaching unprecedented values for June.
The Met Office is warning that the current renewed period of warm weather means the sea surface could have limited opportunity to cool, raising the possibility that the current marine heatwave could intensify further, potentially reaching Category 4, classified as “extreme” - a level rarely recorded in UK waters.
The Copernicus Climate Change Service (C3S) and the Copernicus Marine Service (CMEMS) have confirmed that global sea surface temperatures (SSTs) have surpassed the previous records for this time of year set in 2023 and 2024.
The new seasonal high had been anticipated following the development of El Niño conditions in the Equatorial Pacific, which were formally announced by the World Meteorological Organization (WMO) on 2 June 2026, alongside persistently elevated SSTs observed across several ocean regions in recent months. The record temperatures are expected to have wide-ranging impacts on weather patterns, the global climate, and marine ecosystems
Copernicus have also reported above-average sea-surface temperatures across European seas at the end of June 2026.
UK marine heatwaves
Dr Ségolène Berthou, Air-Sea Interaction Specialist at the Met Office commented:
“Marine heatwaves around the UK have developed rapidly following the recent heat dome, and we are now seeing widespread strong to locally severe conditions.
“This is the third and most intense marine heatwave we have seen this year.
“While these warmer seas did not significantly increase peak temperatures on land, they reduced night-time cooling and helped sustain warmth, particularly in coastal areas.
“With further sunny and calm weather likely next week, there will be little opportunity for the ocean to release this excess heat. This means the surface marine heatwave could intensify further, potentially reaching extreme levels in the south. Such conditions would be highly unusual for UK waters.”
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