September 2023
SUMMARY OF THE METEOROLOGICAL READINGS AT DURHAM UNIVERSITY OBSERVATORY
September 2023
Temperatures (all temperatures in degrees Celsuis; all averages 1991-2020)
Mean daily maximum: 19.7 Difference from average: +2.4
Mean daily minimum: 11.2 Difference from average: +2.0
Mean air temperature: 15.5 Difference from average: +2.2
Absolute maximum: 28.4 (9th)
Absolute minimum: 5.7 (13th)
Mean grass minimum: 9.7 Difference from average: +2.6
Absolute grass minimum: 3.0 (13th)
Mean concrete minimum: 11.7
Absolute concrete minimum: 5.8 (22nd)
Number of ground frosts: 0 Difference from average: -1
Number of air frosts: 0 Difference from average: 0
Mean soil temperature at 300 mm depth: 16.9
Mean soil temperature at 1000 mm depth: 16.2
Rainfall (all totals in millimetres; all averages 1991-2020)
Total for the month: 53.4 Difference from average: -3.4
Percentage of the average: 94%
Wettest day: 11.4 (14th)
Number of rain days (>0.1 mm): 16 Difference from average: +1
Number of wet days (=>1.0 mm): 12
3-month total rainfall to 30th September 2023: 249.6 Difference from average: +64.6
6-month total rainfall to 30th September 2023: 377.8 Difference from average: +36.0
12-month total rainfall to 30th September 2023: 740.6 Difference from average: +59.6
Sunshine (all totals in hours; all averages 1991-2020)
Total for the month: 145.6 Difference from average: +13.5
Percentage of the average: 110%
Mean daily sunshine: 4.9 Difference from average: +0.4
Sunniest day: 10.4 (4th)
Number of days with no recorded sunshine: 1
Note that the monthly sunshine total is now calculated from the UKMO E&NE regional total. Daily sunshine totals quoted here and in the data summary are uncorrected.
Wind (kph; all data from the West Building roof, Lower Mountjoy campus)
Average wind speed: 4.2
Maximum gust: 57.9 (19th, 00:00, W)
Comments on September 2023
September started with some very hot days and even with the expected cooler days later in the month, this still ends up the 2nd equal warmest September (with 2021) on record since 1843, surpassed only in 2006 (15.9 °C). The mean maximum is the third highest on record for September, higher than July’s or August’s this year but lower than June’s. There were four days with a maximum of at least 25 °C, the equal 2nd highest September total (with 1898), one less than the record in 1959. However, there was technically no ‘heatwave’ as there were not three days in a row that reached 25 °C. There have been four September heatwaves at Durham since records began: in 1868, 1880, 1906 and 1959. The mean minimum temperature was the 4th highest for September since 1843 (11.2 °C), exceeded only in 2006 (11.8° C), 2021 (11.4 °C) and 2016 (11.3 °C). The minimum temperature of 16.5 C on the 11th is the 4th warmest September night on record; three Septembers share the highest minimum of 17.2 °C: 1945, 1949 and 2016. As might be expected, there was also the 4th highest mean grass minimum for September since 1874 (9.7 °C), exceeded only in 2021 (11.4 °C), 2000 (10.4 °C) and 2016 (9.8 °C).
A fall of 7.4 mm on 10th September brought to an end a dry spell of 13 days. The wettest day was the 14th with 11.4 mm. Both the number of rain days and the month’s total were close to average. Sunshine was above average, the total of 145.6 hours being just into the upper quartile (n=141).
Emeritus Professor Tim Burt
Department of Geography
Durham University