Thursday, September 07, 2023
A heatwave in September is unusual but not unprecedented.
Dates on which the temperature at Hampstead reached 30°C
| | Jun | Jul | Aug | Sep |
| 2010 | 27 | 9/10 | | |
| 2011 | 27 | | | |
| 2012 | | 25 | 18 | |
| 2013 | | 13 15/16/17 22 | 1 | |
| 2014 | | 18 | | |
| 2015 | | 1 | 22 | |
| 2016 | | 18/19/20 | 24 | 13 |
| 2017 | 17/18/19/20/21 | 6 | | |
| 2018 | | 5/6/7/8 15 23 25/26/27 | 2/3 6/7 | |
| 2019 | 29 | 23/24/25 | 25/26/27 | |
| 2020 | 24/25/26 | 31 | 7/8/9/10/11/12 | |
| 2021 | | 18/19/20 | | |
| 2022 | 17 | 11/12 17/18/19 | 11/12/13/14 | |
| 2023 | 11 25 | | | 6/7 9/10 |
» in red: reached 33°C
» in red & bold: reached 35°C
» in red & bold & underlined: reached 37°C
But Hampstead's a bit cooler than central London, being 40m higher up.
And London's not entirely representative of the whole UK.
So here's a better table covering the entire country.
Dates on which the temperature somewhere in the UK exceeded 30°C
| | May | Jun | Jul | Aug | Sep | total |
| 2010 | 23 | 27 | 9/10 | | | 4 |
| 2011 | | 27 | | 3 | | 2 |
| 2012 | 25 | | 24/25 | 18/19 | | 5 |
| 2013 | | | 13/14/15/16/17/18/19/20 22 | 1 | 5 | 11 |
| 2014 | | | 18 24 26 | | | 3 |
| 2015 | | 30 | 1 | 22 | | 3 |
| 2016 | | | 18/19/20 | 23/24 | 13/14/15 | 8 |
| 2017 | | 17/18/19/20/21 | 6/7 | | | 7 |
| 2018 | | 25/26/27/28/29/30 | 1/2/3 5/6/7/8/9 15/16
22/23/24/25/26/27 | 2/3/4/5/6/7 | | 28 |
| 2019 | | 28/29 | 22/23/24/25 | 24/25/26/27 | | 10 |
| 2020 | | 24/25/26 | 31 | 6/7/8/9/10/11/12 | 15 | 12 |
| 2021 | | | 17/18/19/20/21/22/23 | | 7/8 | 9 |
| 2022 | | 17 | 8 10/11/12/13 17/18/19 24 | 8/9/10/11/12/13/14/15 | | 18 |
| 2023 | | 10/11/12/13 25 | 7 | | 4/5/6/7/8/9/10 | 13 |
The data is from Dan Harris, Deputy Chief Meteorologist at the Met Office, who tweets a lot at @RoostWeather.
Note that...
About half of 'over 30°C' days are in July and about a quarter in August.
The number of 'over 30°C' days is increasing - 2018-2023 had double 2010-2017.
This year we had a proper splurge of 'over 30°C days' in June.
But in July the only place to reach 30°C was Chertsey on the 7th, and that was only 30.2°C.
And in August nowhere in the UK reached 30°C at all.
It's been the least heated July and August since 2011.
But September is proving a different matter.
It's very rare to get a prolonged hot spell in September.
Previously the UK record for 'consecutive September days exceeding 30°C' was three.
Yesterday we equalled that record, today we break it and by the weekend we'll have smashed it.
It's also very rare that the warmest day of the year is in September.
This last happened in 2016, and before that 1962.
Unusual weather happens every year, and this isn't necessarily any more unusual than normal.
Climate-wise, one year's weather proves nothing.
But years with high temperatures are coming thicker and faster recently.
Over the last 50 years...
Years that didn't reach 30°C: 1974, 1978, 1980, 1981, 1993
Years that exceeded 33°C: 1975, 1976, 1989, 1990, 1994, 1995, 1996, 1997, 2003, 2006, 2011, 2013, 2015, 2016, 2017, 2018, 2019, 2020, 2022, 2023
Years that exceeded 35°C: 1976, 1990, 1995, 2003, 2006, 2015, 2018, 2019, 2020, 2022
Years that exceeded 37°C: 1990, 2003, 2019, 2020, 2022
Years that exceeded 40°C: 2022
Brace yourself for hotter Septembers, indeed hotter weather overall.
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