September 2007

Temperatures
(all temperatures in degrees Celsius; all averages 1961 – 1990)

Mean daily maximum: 17.5
Difference from average: +0.8

Mean daily minimum: 8.8
Difference from average: +0.1

Mean air temperature: 13.2
Difference from average: +0.5

Absolute maximum: 23.4 (6th)

Absolute minimum: 2.6 (18th)

Mean grass minimum: 6.1

Absolute grass minimum: -1.2 (4th)

Number of ground frosts: 3

Number of air frosts: 0

Mean soil temperature at 30cm depth: 15.3

Mean soil temperature at 100cm depth: 15.7

Rainfall
(all totals in millimetres; all averages 1961 – 1990)

Total for the month: 39.4
Difference from average: -16.2

Percentage of the average: 71%

Wettest day: 8.2 (21st)

Number of rain days (>0.25mm): 10

Number of wet days (=> 1mm): 7

3-month total rainfall to 30th September: 182
Difference from average: +7.8

6-month rainfall total to 30th September: 353.6
Difference from average: +28.3

12-month rainfall total to 30th September: 735.4
Difference from average: +86.4

Humidity
(Averages for 09:00 hours GMT)

Relative Humidity: 77%

Sunshine
(all averages 1961 – 1990)

Total for the month: 106.1 hours
Difference from average: -17.9

Percentage of the average: 86%

Mean daily sunshine: 3.5 hours
Difference from average: -0.6

Sunniest day: 10.7 hours (6th)

Number of days with no recorded sunshine: 0

Cumulative total sunshine since 1st January: 1095.5 hours
Difference from average: -28.9

Wind

The mean wind speed: 11.3km/h [6.1kt]
Difference from average: -1.0km/hr

The highest gust: 87km/h [47kt] from 191° at 12:04 GMT on 15th

ISSN1350-483

Comments on September 2007
September was above average temperature but not nearly as warm as September 2006. Nevertheless, the 12-month mean remains above 10°C, as it has done all this year. Daytime temperatures were above average (not remarkably so), whereas night-time temperatures only just above average.

It was a dry month, with the lowest number of rain days since 1985. Even so, long-term totals all remain above average. It was the first September since 1988 with sunshine every day, but even so, the overall total amount of sunshine was below average.

Professor Tim Burt
Department of Geography
Durham University