The media has recently suggested that this August looked set for further high temperatures. Whether this occurs or not, August is synonymous in many people’s minds with seeing the best of the summer weather in the UK. In fact, although August often does see the hottest temperatures of the year this is not always the case. It contains the hottest day of the year only once in every four years, slightly less than June.
Balanced against the warmer sea temperatures during August we have to put its shorter days and correspondingly lower sunshine hours, with the strength of the sun less strong as each day passes. This usually means that overall August is slightly cooler normally than July, especially in the south east of England.
Nevertheless, nearly all the very hottest days recorded have been in August. In the last century the August days that stand out occurred in 1911, 1932 and 1990 as well 2003 of course, when the highest (official) Temperature ever recorded in the UK was reported. Most of our exceptionally hot days occur under similar meteorological conditions. They need a very warm plume of air carried north east across the continent from Iberia, where it has already been heated by strong insolation. The short sea crossing helps also. Years in which the ground is very dry as a result of a period of dry weather are also prone to seeing high temperatures, as the sun’s energy isn’t used evaporating ground moisture.
Almost all of August 1911 was very hot and dry as high pressure dominated the weather. However the 9th was exceptionally hot and as high pressure moved to the north east with a light SE’ly flow from France, the mercury reached 98F (36.7C) at Raunds in Northamptonshire and also Canterbury (Kent).
Another very hot August day occurred in 1932. An area of high pressure over the Midlands and a thundery low that developed over Biscay allowed a very hot plume of air into the south by the 18th. This allowed temperatures to reach 36.1C at Halstead in Essex, not quite so hot as in 1911. Some severe storms followed, with flash flooding in places, breaking the hot spell by the 20th.
It wasn’t until August 1990 that the record’s set above were surpassed. With the classic hot dry weather pattern in place by as early as the 1st, 33C was recorded at both Jersey and Heathrow with 34C on the 2nd. As the air mass stagnated by the 3rd with a very warm upper plume across the south east, Cheltenham (Gloucs) reported the official highest maximum temperature with 37.1C, at that time the highest temperature ever recorded. Interestingly the record for the highest minimum recorded was also set on that night (3rd-4th) in Brighton, of 23.9C.
Until recently many meteorologists considered the ‘100F’ mark unobtainable in the UK. Indeed in 1952 Gordon Manley in his classic book ‘Climate and the British Scene’ (Collins, 1952) suggested such ‘the highest figure we are ever likely to get in the hottest parts of Southern Britain lies very close to 100F’. This may still be the case but on August 10th 2003 the temperature did indeed exceed this figure and received enormous press coverage as a result.
Temperatures built up gradually early in August 2003 with 36.4C recorded at Wisley on the 6th and 36.9C at Enfield by the 9th. On the 10th as the air stagnated further a new record of 38.5C (101.3 F) was set at Brogdale near Faversham (Kent) and in outer London 38.1C was reported at Kew Gardens (Surrey).
As to whether the 40C record will ever be surpassed in the UK there are those who now think it is achievable. It is worth remembering that such high figures are at least partially dependant on instrument siting. In location prone to local heating effects, it is just possible that on very hot days (like the 10th August 2003) such a temperature may have already been reached in the shade somewhere in the UK. However, without the approved instruments there to record it, we will never know!
