Sea temperature reading is latest landmark in summer of weather records

A SUMMER of heatwaves and weather records in Jersey reached another landmark as a sea temperature of 20°C was recorded.

The figure from Thursday evening’s high tide – although “downgraded” to 19.9°C once the daily average of the two most recent high tides had been calculated yesterday morning – marked further evidence of a long-term trend that has been described as contributing to a marine heatwave.

Data provided by Jersey Met showed that the sea temperature has been above the long-term average since 2022, with notably high figures in recent months.

The June figure was 16.2°C, 1.4°C above the average for 1991 to 2020, while the margin increased to 1.7°C above average in July, when a figure of 18.6°C across the month was recorded.

The seas around the British Isles have been getting steadily warmer since the 1980s, driven by climate change.

Dr Ségolène Berthou of the UK Met Office said: “We are likely to see marine heatwave conditions becoming average towards the middle-to-end of the century and this is projected to increase if we don’t cut greenhouse gas emissions.”

Researchers have also noticed longer-term shifts in marine life, with cool-adapted species such as cod generally moving further north, while numbers of some warm-water species such as octopus have risen around south-west England and in the waters around the Channel Islands.

Although there have been 22 individual days when Jersey has recorded a daily sea temperature of 20°C or higher, the most recent instance was in August 2003. The highest figure on record dates from 8 September 1989, when a mark of 20.7°C was logged.

Jersey’s fourth heatwave of 2026 ended officially yesterday as the maximum temperature fell just short of the 28°C threshold after three days above this mark. But it was still one of the hottest days for the Battle of Flowers on record, just behind the 28.1°C recorded in both 1909 and 1995, and behind the record figure of 2022 – 31.9°C.

A maximum figure of 35.6°C was recorded at Jersey Airport on Wednesday – the seventh highest daily maximum on record. With the effects of climate change more pronounced than ever, with a series of wildfires around Europe, seven of Jersey’s 20 hottest days on record have been registered this year.

Slightly cooler temperatures are forecast for the weekend, with predicted daily highs of 26°C on both days, while the Jersey Met forecast for next week shows a chance of some rain on Tuesday and Wednesday.