Climatic change prompted by a weaker jet stream is likely to lead to more frequent heatwaves, a senior meteorologist has said.
Reacting to data showing the island had experienced its warmest May on record, as well as the warmest-ever spring, Jersey Met said this was part of a trend that had seen weather records broken with increasing regularity.
Senior forecaster Matt Winter said the recent heatwave had been “exceptionally unusual”.
Several records were broken by big margins, including:
- The record high for May, with the previous high for the month of 28.9°C increasing by more than five degrees to a figure of 34.2°C.
- An overnight “low” of 22.0°C – 4.5°C above the previous May figure and one of the six hottest nights on record for any time of year.
- The longest stretch (at any time of year) of consecutive daily highs above 30°C – five.
- The average temperature across the whole of May was 16.5°C, breaking the previous record, set in 2008, by 0.7°C.
- Jersey’s warmest-ever spring, with the average temperature across March, April and May being 13.5°C, beating the record of 12.7°C, set just last year.
Mr Winter said: “When you’ve got data going back 130 years, you would expect any new records [for a particular month or season] to be perhaps a tenth of a degree or two higher, so to have the May and spring records broken by 0.7°C and 0.8°C is really quite something.”
The effects of climate change were being seen in more intense periods of heat, he added.
“With a weaker jet-stream, we are liable to see the sort of blocking high that we saw last week,” explained Mr Winter.
“It acted as a bit of a ‘lid’, stopping the heat dissipating and causing the temperature to build up day after day.”
Once the “block” was shifted over the weekend, a contrasting spell of weather has dominated the forecast this week, with westerly winds, far cooler temperatures and significant rainfall.
A total of 21.7 millimetres of rain was recorded at Maison St Louis in St Helier on Monday night and early yesterday morning, while yesterday’s maximum of 18°C was the first daily high below 20°C since 20 May, and 16 degrees cooler than the previous Tuesday.
The rainfall will have been welcomed by gardeners, the potato industry and those who look after sports grounds – it was described as “liquid gold” by Jim Perchard of Farmers Cricket Club.
Jersey Water said last week that although water use had been well above average, in line with the pattern experienced during hot weather, reservoir stocks were 96% full [on 27 May].
A spokesperson for the utility company said: “We do not have any imminent concerns, but as the island only has 120 days of water when the reservoirs are full, we always ask people to use water wisely to avoid the need for restrictions, such as hosepipe bans.”
Mr Winter said that while more frequent periods of extreme weather were associated with climate change, the arrival of a heatwave so early in the year was not necessarily a guide to whether the summer of 2026 would be correspondingly hot.
