“While temperatures could peak at 27°C next week, with the highest temperatures expected in the south of England and only possibly lasting a couple of days, next week’s conditions are likely to fall just outside of official Met Office heatwave thresholds,” the agency added.
Though not officially a heatwave, the abnormally high land temperatures in the UK, especially in its southern parts, are closely tied to the warmer than usual SSTs in the North Atlantic Ocean, which makes the heat event transboundary.
Such transboundary heatwaves that occur over both land and ocean and move from one to the other are more extensive, last longer and are more severe than heatwaves that occur only on land or over ocean, according to a new study published in the journal Nature Communications on April 10 2025.
The study showcased a major gap in the understanding of heatwaves that needs to be fixed, especially in the tropical regions of the planet.
The report defined a heatwave as a period when mean surface air temperature exceeds the 90th percentile threshold during the warm seasons. This means that the recorded temperature values are higher than 90 per cent of all temperature values in a particular reference period.
Transboundary heatwaves are rarer than land-only or ocean-only heatwaves but are going to increase in frequency with global warming and consequent climate change, according to the study.
The study conducted by scientists from the China University of Geosciences, Sun Yat-sen University and The Chinese University of Hong Kong found that there were a total of 14,830 heat wave events in between 1981 and 2020.
Out of these, the maximum number of events — 8,145 — occurred only on the ocean and 3,198 events occurred only on land, according to the study. As many as 2,133 heatwaves travelled from ocean to land, like the heat event in the UK; those that travelled from land to ocean were the rarest. occurring 1,354 times.
Some land and ocean regions were more prone to transboundary heat waves. Ocean-to-land heatwaves (OTLH) occurred with higher frequency, larger spatial coverage and greater intensity in western South America, central Africa, southern Europe and eastern Asia.
The land-to-ocean heatwaves (LTOH) increased with latitude in the northern hemisphere and are severe and extensive in the Atlantic and Southern Oceans.
OTLHs and LTOHs are generally more persistent, extensive and severe than land-only and ocean-only heatwaves. OTLHs can last up to nine days on an average whole LTOHs can last for eight days on an average.
OTLHs can occur on average over an area of 6.33 million square kilometres which is almost double the size of India and LTOHs can occur on average over an area of 4.24 million square kilometres which is 1.3 times the size of India.