A prolonged marine heatwave affecting UK waters is poised to intensify to extreme levels next week, forecasters have warned.
The Met Office reports that surface waters across north-west European seas are currently experiencing conditions ranging from moderate to severe, with many areas classified as “strong” and some even “severe”.
These elevated temperatures mean waters have already reached levels typically seen in August, averaging 2C above the norm.
Locally, some offshore regions along the English and Welsh coasts are experiencing temperatures more than 4-5C higher than usual.
open image in galleryExperts warn that these record-breaking temperatures are expected to have significant repercussions for weather patterns, the global climate, and marine ecosystems, potentially altering fish populations and harming numerous species.
This surge in sea-surface temperatures follows last week’s unprecedented heatwave, which was exacerbated by climate change and a “heat dome” that lingered over Europe, trapping heat for days.
The hot spell saw temperatures break the record for the hottest June day – set 50 years ago during the infamous 1976 summer – by more than 1C.
After a brief cooler spell, forecasters say conditions are set to heat up again next week, with parts of South East England potentially seeing temperatures of over 30C.
This means the sea surface will have limited opportunity to cool after last week’s hot spell, increasing the possibility that the current marine heatwave reaches an “extreme” classification – a level rarely recorded in UK waters, the Met Office said.
It comes as the English Channel has been experiencing marine heatwave conditions for much of 2026, making this region particularly susceptible to further warming.
Meanwhile, surface temperature anomalies in parts of the North Sea are forecast to peak at around 4-5C above average in the coming days.
open image in galleryDr 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 surpassed the previous records for this time of year set in 2023 and 2024.
These new seasonal highs had been anticipated following the development of the El Nino weather phenomenon, which sees the warming of sea surface temperature in the tropical Pacific Ocean push up global temperatures.
El Nino conditions were formally announced by the UN’s World Meteorological Organisation (WMO) last month, coming alongside higher-than-normal surface sea temperatures seen across several 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 cited the recent example of a population bloom of common octopus, which has been having “serious negative consequences” for crab and lobster fisheries in South West England.
Despite warmer than usual marine temperatures, the public is still being warned about the risks 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.”
Where possible, always choose an RNLI lifeguarded beach, and swim between the red and yellow flags, and to call 999 for the coastguard in the cast of an emergency, the Met Office added.