Record-breaking June heatwave on the way?

Temperatures are on the rise through this week, as high pressure builds across the UK and acts as a lid on the building warmth, preventing its escape. It is likely we will enter heatwave territory later this week across England, perhaps up to 6 days - lasting well into next week. Temperatures could reach 30C or more as early as Friday, with the upper bounds of model ensembles suggesting temperatures as high 34-35C on Saturday and Sunday. However, the 12z GFS shows temperatures reaching 38C on Monday, this would be a new record high for June in the UK, though seems unlikely.

However, the 06z and 12z GFS are hot runs for England and Wales, 5 consecutive days Sat-Weds with a number of places reaching 30C or more, Sun & Mon looking very hot, with 35-36C, which, if near, could challenge the hottest June temp on record of 35.6C set at Southampton on 26 June 1976. 12z GFS was a slight outlier for 2m temp in London for Sun and Mon against the ensembles though. The 06z and 12z GFS differs from the 00z run, by not being so progressive with moving the upper trough east and introducing cooler and fresher conditions by early next week, but instead slowing and amplifying the trough more to bring the classic set-up to bring a hot plume to the UK that lasts well into next week.

Hot conditions look to develop from Friday, as an upper trough stalls and amplifies to the west of Europe, which will pull hot air north from Iberia across the UK. 

The UK’s hottest June day on record is 28th June 1976 with 35.6 °C at Southampton Mayflower Park, so there is potential that this record may be challenged. Such high temperatures in June are not that common either. Maximum temperatures of 33 °C or more in June have occurred on less than 1 per cent of June days since 1961, with 34 °C or more registered just 5 times in June since 1961, mainly in the exceptional heat of late June 1976.

Reaching 33C or more was quite unusual in England and Wales until recent years, especially early in month, unheard of in Scotland or Northern Ireland. 33C in June hasn’t happened since 25th June 2020, the last time 34C was reached was on 29th June 2019.

The UK’s warmest June on record was a recent as 2023. The average UK mean temperature of 15.8°C, which is 2.5 °C above average, is the highest in a series since 1884, with all four home nations reporting their warmest June on record. The highest temperature that month reached was 32.2C at Chertsey, Surrey on the 10th and at Coningsby, Lincs on the 26th. 

The start of June 2023 and June this year bear the similarities that both were in the midst of a marine heatwave around the British Isles and NE Atlantic that started earlier in Spring. In late May this year, a marine heatwave lasting over two months, due to persistent warm and settled weather, brought sea surface temperatures up to 4°C warmer than average west of Ireland, and by 1.5-2.5°C around the UK coastline. June 2023 saw water temperatures as high 4-5C above normal The warmer waters that June and this June so far likely playing a role in raising temperatures overland. SSTs aren’t as high as they were at this point in June 2023, but are likely keeping temperatures elevated.

Marine heatwave in June 2023 coincided with the hottest June on record for the UK.

A marine heatwave in May this year to the west of Ireland.

So, with the potential for temperatures to reach the mid=30s Celsius this weekend and early next weel in England, we are not far off reaching or breaching the highest June temperature for the UK since records began. And even though it may cool off as early as Sunday, but more likely early or middle of next week, perhaps with a thundery breakdown, there are signs from the GFS and ECMWF model ensembles that heat may return again later this month, with another stab at the record, as temperatures so easily climb into the 30s these days after day or two of a hot air plume wafting up from NW Africa and Iberia.