A marine heatwave (MHW) - a prolonged period of unusually warm sea surface temperatures - has been intensifying around the UK’s coastline, particularly the southern half, since February. By the end of May, sea temperatures were up to 2oC warmer than usual, peaking in the western English Channel, for this time of year.
What does the current marine heatwave look like?
In early June, the MHW deteriorated due to increased cloud cover and wind speeds. Following last week’s record-breaking UK temperatures, the majority of the Northwest European Shelf is experiencing a category I-III event. By the end of June, parts of UK waters were up to 5oC above average.
Dr. Zoe Jacobs, a scientist at the National Oceanography Centre (NOC), is closely monitoring this unfolding situation. In this article, she provides regular updates on how the MHW is developing, what the latest satellite data shows, and why it matters for UK marine ecosystems, fisheries, and communities.
Why does this matter?
Globally, MHWs have caused wide-ranging impacts on marine ecosystems. This includes the mortality of key species such as seagrass and kelp, the mortality or reorganisation of commercial fisheries and the initiation of harmful algal blooms (HABs).
The biological and societal impacts of this MHW are currently unknown. However, impacts may emerge over the coming weeks, including affecting the timing and size of phytoplankton blooms (base of the marine food chain), potentially reducing or boosting their productivity. It’s possible that Harmful Algal Blooms could be triggered, which can produce toxins harmful to marine life and the environment.
It may also lead to a temporary disappearance of cool-water species and emergence of warm-water species or the disruption of marine species’ life cycles , impacting their growth or reproduction. All of this may impact the regional marine ecosystem, fisheries and the economy in different ways.
With climate change continuing to raise global temperatures, it’s vital that these occurrences are monitored, and that we have more targeted research to understand these impacts to improve UK resilience to MHWs.
Rolling Updates: Marine Heatwave Monitoring
Read our updates below on the developing MHW around the UK using satellite maps of sea surface temperature (SST)
Latest: Monday 29 June 2026
On Monday 29 June, most of the Northwest European Shelf was experiencing at least a category I MHW, where SSTs were 1-5oC warmer than usual. The North Sea and parts of the English Channel appear to be experiencing the greatest warming with widespread anomalies of 3-5oC as temperatures rise to more than 18oC. Parts of the UK coastline are currently up to 4oC warmer than usual including south Devon and near the Thames estuary, with warming of up to 3oC apparent around the southeast coast, in the western English Channel and parts of northwest Wales and English coastlines.
The event is currently most intense in the southern part of the UK with smaller anomalies of 1-2oC currently occurring around Scottish, Irish and northeast English coastlines.
With UK air temperatures set to rise to above 30oC in some regions by early next week, the MHW is likely to persist or intensify.
29.06.26: Sea Surface Temperature (left), respective anomalies (middle) and Marine Heatwave category (right). Calculated using the 0.05o daily OSTIA Sea Surface Temperature product using a baseline of 1991-2020.
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What Do We Know About Marine Heatwaves Around the UK?
A study led by NOC's Dr Zoe Jacobs revealed where marine heatwave events are most likely to occur in UK waters, for the first time. Published in Frontiers in Marine Science, it shows there are regional marine heatwave hotspots in the Southern North Sea and English Channel. Events here are weaker than in other areas around the UK, but last longer.
Related Resources
Learn more about marine heatwaves and NOC's research aimed at learning more about their behaviour below. This includes educational pages and latest news.
