Warm Spells in September

Introduction
The hot and summerlike spell of weather over most of the UK during the first part of September 1999 had a few weathermen and women reaching for the record books because it was the first time in quite some time that such a hot spell of weather had affected the UK in September.

Philip Edenís book Weatherwise tells readers that whilst temperatures exceed 27C somewhere around the UK about once every two years on average spells of two or three days above 27C over a large part of the UK are much rarer and during the last 25-30 years have only happened in 1973, 1982, 1991 and 1999.

Now, given that many recent winters have been milder than average and certainly less snowy than they were in, say, the 1960ís, 70ís and 80ís and considering most Julys and Augusts in the 1990's were warmer than average it might come as a little bit of a surprise to find that great September heat waves appear to have become less and less common over the course of the 20th century. It should, however, be pointed out that it is not clear whether this is some kind of long term trend or simply a statistical coincidence.

Between 1895 and 1973 a reading of 30C or happened in 16 years, or on average once every 5 years. Since then, the highest September temperatures have been 30.4C at Gravesend on September 11th 1999 and 29.8C at Marholm near Peterborough on September 1st 1991. Temperatures have not exceeded 32C in September for 50 years; 1949 was the last time and this also happened in 1906, 1911, 1919, 1926 and 1929.

Memorable September Hot Spells/Days
4th September 1880 - highs reached 30.7C in Loughbrough. Nationally this was the hottest day of the year.

6th September 1890 - highs reached 28.3C in Llandovery, Dyfed. Nationally this was the hottest day of the year.

10th September 1891 - highs reached 30C in Loughbrough. Nationally this was the hottest day of the year.

23rd to 29th September 1895 - highs reached 30.6C in Strathfield Turgis in Hampshire on the 25th and 27th. Nationally these days were the hottest days of the year. As well as being the latest dates in the year on which 30C has been recorded, these are also the latest dates between 1875 and 2000 on which the hottest day of the year has been registered. During the rest of this period temperatures exceeded 27C somewhere around the UK.

7th September 1898 - highs reached 33.4C in Norwood, London. Nationally this was the hottest day of the year.

31st August to 3rd September 1906 - this is the most impressive September heat wave of the 20th century. A large part of the UK reached 32C or more on each of these 4 days. The 2nd was the hottest day in most areas; Bawtry near Doncaster reached 35.6C, Barnet, Maidenhead and Epsom reached 35C and Whitby reached 34.3C. Places in Wales near Chester and Gordon Castle near Elgin in Scotland reached 32C. Taking the UK as a whole, the 2nd was the hottest day of the year. Some countiesí (in northern England and Scotland primarily) hottest days on record were set during this heat wave. The 2nd is also the 8th equal hottest day of the 20th century and the hottest September day on record as well as being one of only 23 days in the 20th century where temperatures topped 35C.

5th to 8th September 1911 - temperatures exceeded 32C somewhere over the UK on each of these 3 days and the hottest place was Raunds in Northamptonshire where highs reached 34.6C. However, such was the tremendous heat of the 1906 September heat wave that Raundsí high is only the 8th hottest September temperature recorded in the UK this century!

11th September 1919 - Kew recorded a high of 82.8F. Raunds in Northamptonshire, meanwhile, reached 32.2C and nationally this was the hottest day of the year.

18th to 20th September 1926 - on the 19th Camden Square in London reached 32.2C. Nationally this was also the hottest day of the year.

4th to 8th September 1929 - on the 4th temperatures reached 84.6F at Kew whilst Newport on the Isle of Wight reached 32.2C on the 8th.

4th September 1940 - Rickmansworth recorded a high of 32.3C.

15th and 16th September 1947 - temperatures reached 28.9C in Southend on the 15th and 31.1C in Norwich on the 16th.

4th to 5th September 1949 - at Kew highs reached 85.8F on the 4th whilst at Maldon in Essex temperatures reached 32.8C on the 5th. This is the last time a September day in the UK exceeded 32C.

1st September 1954 - highs reached 30.6C at Camden Square, London. Nationally this was the hottest day of the year.

3rd September 1962 - highs reached 27.8C at Writtle, Essex. Nationally this was the hottest day of the year.

5th September 1973 - temperatures reached 30C at London Weather Centre and this is the highest September maximum recorded here since records began here in 1940. Before 1999 this was also the last time a reading of 30C had been recorded around the UK in September.

13th to 18th September 1982 - much of central and south-eastern England had a spell of hot and sunny days. Highs reached 27C somewhere on the 15th and 18th and 29C was recorded in Jersey on the 17th whilst Heathrow recorded 28.3C on the 18th.

1st to 3rd September 1991 - during this 3 day period temperatures reached 29C somewhere around the UK and the high of 29.7C at Heathrow and London Weather Centre and 29.8C at Marholm near Peterborough on the 1st made this day the hottest day of the year over the UK. Until 1999 these were also the highest September temperatures recorded since 1973.

September 1st to 11th 1999 - the first part of September 1999 was one of the most notable September heatwaves of the 20th century. On ten of these eleven days temperatures reached or exceeded 25C somewhere around the UK and on seven of these eleven days temperatures of at least 27C were recorded at one or more sites. The two hottest days were the 5th, when Mildenhall reached 30C, and the 11th when Gravesend registered a high of 30.4C, the warmest September day since 1973 and the highest so late in the year since 1947.

References/Sources
EDEN, PHILIP (1995) Weatherwise. Macmillan, pp323.
STIRLING, ROBIN (1997). The Weather of Britain. Giles de la Mare, pp304.
Weather Log September 1999, 1991 & 1973

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Dan Suri, 16 February 2001