September 2025
SUMMARY OF THE METEOROLOGICAL READINGSAT DURHAM UNIVERSITY OBSERVATORY
September 2025
Temperatures (all temperatures in degrees Celsuis; all averages 1991-2020)
Mean daily maximum: 17.6 Difference from average: +0.3
Mean daily minimum: 8.8 Difference from average: -0.4
Mean air temperature: 13.2 Difference from average: -0.1
Absolute maximum: 21.8 (7th)
Absolute minimum: 2.3 (22nd)
Mean grass minimum: 7.2 Difference from average: +0.1
Absolute grass minimum: -0.4 (22nd)
Mean concrete minimum: 8.5
Absolute concrete minimum: 2.0 (22nd)
Number of ground frosts: 1 Difference from average: 0
Number of air frosts: 0 Difference from average: 0
Mean soil temperature at 300 mm depth: 15.4
Mean soil temperature at 1000 mm depth: 15.4
Rainfall (all totals in millimetres; all averages 1991-2020)
Total for the month: 79.0 Difference from average: +22.2
Percentage of the average: 139%
Wettest day: 32.4 (20th)
Number of rain days (>0.1 mm): 18 Difference from average: +3
Number of wet days (=>1.0 mm): 15
3-month total rainfall to 30th September 2025: 153.8 Difference from average: -31.2
6-month total rainfall to 30th September 2025: 217.2 Difference from average: -167.4
12-month total rainfall to 30th September 2025: 476.2 Difference from average: 186.0
Sunshine (all totals in hours; all averages 1991-2020)
Total for the month: 150.0 Difference from average: +17.9
Percentage of the average: 114%
Mean daily sunshine: 4.8 Difference from average: +0.4
Sunniest day: 7.7 (16th) 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: 1.2
Maximum gust: 13.9 (15th, 11:45, WSW)
Pressure (mbar)
Average: 1011.2
Maximum: 1031.5 (24th, 08:45) Minimum: 987.2 (15th, 04:45)
Comments on September 2025
For the first time since January, we had a month with its mean air temperature below the 1991-2020 average, albeit by only a tiny amount. Even so, this was the equal 51st warmest September in Durham since 1843, confirming the occurrence of global warming in recent decades. This mean air temperature is therefore just outside the upper quartile. It was warmer than September 2024. Days were a little above average but nights below average.
Rainfall was above average for the month. The fall of 32.4 mm on the 20th was the 13th wettest September day since 1850, resulting from an active cold front moving slowly across northern England. Rainfall fell for 16 consecutive hours with a maximum hourly intensity of 4.4 mm per hour (17:00 – 18:00). Despite above-average rainfall, it was the 30th sunniest September in 143 years.
I have had my doubts about the wind speed measurements from the automatic weather station on the roof of the West Building for some months. The recently reported figures are best treated with caution therefore. I will ask for the AWS to be checked.
Emeritus Professor Tim Burt
Department of Geography
Durham University