The Met Office has warned that UK waters are experiencing a long-lasting marine heatwave with risk of hitting rare ‘extreme’ levels next week as temperatures are expected to break records again
The Met Office has issued a new ‘extreme’ heatwave warning as UK waters could reach ‘severe’ levels next week.
The prolonged marine heatwave affecting UK waters throughout much of 2026 is set to escalate next week as temperatures of 39C are forecast.
According to the Met Office surface waters in north-west European seas are presently experiencing moderate to severe marine heatwave conditions, with numerous areas currently classified as “strong” and some “severe”.
This indicates waters have climbed to temperatures typically anticipated in August and are on average 2C above normal.
In some areas of the English and Welsh coastlines, temperatures have climbed more than 4-5C.
Specialists suggest these record-breaking temperatures are likely to have far-reaching consequences on weather systems, the global climate and ecosystems, triggering changes in fish populations and harming numerous marine species.
This follows the raised sea-surface temperatures which surged in recent days, partially due to last week’s exceptional heatwave, fuelled by climate change and a “heat dome” that became stationary over Europe and confined heat for several days.
The sweltering period witnessed temperatures shatter the record for the warmest June day – established 50 years ago during the notorious 1976 summer – by more than 1C.
Following a short cooler period, forecasters indicate conditions are poised to warm up once more next week, with sections of South East England potentially experiencing temperatures reaching 39C.
This means the sea surface will have little chance to cool down following last week’s heatwave, raising the likelihood that the ongoing marine heatwave could reach an “extreme” classification – a level rarely seen in UK waters, according to the Met Office.
The English Channel has been experiencing marine heatwave conditions for much of 2026, making this area especially vulnerable to additional warming.
According to Net Weather maps the UK can expect to see the extreme highs peak on Thursday, July 9 as London is expected to reach a whopping 39C.
According to the Net Weather maps the capital and nearby Berkshire are expected to reach 39C, with Hertfordshire also forecast to climb to 38C.
Dr Segolene Berthou, air-sea interaction specialist at the Met Office, said: “Such conditions would be highly unusual for UK waters.
“Marine heatwaves around the UK have developed rapidly following the recent heat dome, and we are now seeing widespread strong to locally severe conditions.
“With further sunny and calm weather likely next week, there will be little opportunity for the ocean to release this excess heat.”
Earlier this week, the EU’s Copernicus Climate Change Service and the Copernicus Marine Service confirmed that global sea surface temperatures have exceeded previous records for this time of year, which were set in 2023 and 2024.
These new seasonal peaks had been expected following the emergence of the El Nino weather phenomenon, which sees warming sea surface temperatures in the tropical Pacific Ocean drive up global temperatures.
El Nino conditions were formally declared by the UN’s World Meteorological Organisation (WMO) last month, coinciding with above-average surface sea temperatures recorded across numerous ocean regions in recent months.
John K Pinnegar, principal scientist and lead advisor for climate change at the Government’s Centre for Environment, Fisheries and Aquaculture Science, said: “Marine heatwaves can have significant impacts on ecosystems and wildlife.
“Prolonged periods of unusually warm sea temperatures can lead to shifts in fish populations, damage important habitats such as seagrass and kelp, and increase the likelihood of harmful algal blooms.
“These changes can result in mass-mortality events for some marine species and alter the distribution of commercially-important fish and shellfish.
“Prolonged periods of elevated seawater temperatures can also encourage new species to visit UK waters, establish new populations, potentially shaking up UK ecosystems.”
He pointed to the recent case of a population bloom of common octopus, which has been having “serious negative consequences” for crab and lobster fisheries in South West England.
Despite the warmer than average sea temperatures, members of the public are still being cautioned about the very real dangers of cold water shock. Holly Clements, Met Office head of warnings and guidance, said: “With warmer weather approaching, and even with marine heatwave conditions, it’s important to remember that the water around the UK is still cold. Entering it unexpectedly can lead to cold-water shock.”
The Met Office also advised that wherever possible, swimmers should opt for RNLI lifeguarded beaches, stay between the red and yellow flags, and dial 999 for the coastguard in the event of an emergency.
