Weather in South London during September 2009
A dry, anticyclonic month with no measurable rain after the 15th. It was the driest September in South London for 5 years.
Temperatures
The average maximum temperature during September 2009 was 20.0 Celsius (68F), and that was 0.1 Celsius (0.2F) above the 20-year normal, but 0.9 degrees Celsius (1.7F) above the 100-year normal. The average minimum temperature was 11.4 Celsius (52F), and that was 0.4 Celsius (0.8F) above the 20-year average, and 0.8 Celsius above the 100-year normal.
The highest temperature recorded during September was 27.2 Celsius (81F) on the 8th, but the next warmest day was the 19th with only 23.6 Celsius (75F). However, there were a further 13 days, distributed fairly evenly through the month, when maxima were between 20 and 22 Celsius (68-72F). On most other days the top temperatures were between 18 and 20 Celsius (64-68F), but on the 15th the high was only 15.7 Celsius (60F), the coolest day of the month.
There was only 1 warm night during September, the 7th/8th with a minimum of 17.1 Celsius (63F). The next warmest night was that of the 22nd/23rd with a low of 14.8 Celsius (59F). There were 5 other nights when the temperature failed to dip below 14 Celsius (57F). On 8 nights the temperature fell below 10 Celsius (50F), with 6 of these chilly nights occurring during the last week. On 3 nights the minimum was below 7 Celsius (45F): the 17th/18th, 25th/26th and on the following night, which was the coldest of the month, with a low of 6.0 Celsius (43F).
Frost
There were no air or grass frosts during September. A grass minimum of 2.5 Celsius (37F) occurred on the night of the 26th/27th with 5 other nights, including 3 during the last week, when the grass reading was below 5 Celsius (41F).
Rain
A total of 23.6 millimetres (0.9ins) of rain fell during September, and that was only around 40% of average. Measurable rain only fell on 4 days, 8 below average, and remarkably there were only 2 wet days (1.0mm/0.04 ins, or more) and that was 7 days below average. The wettest day was the 15th with 12.9 millimetres (0.5 ins) and the only other wet day was the 2nd with 9.6 millimetres (0.4 ins). No measurable rain fell after the 15th.
Thunderstorms
For the 3rd consecutive September no thunderstorms were observed in this part of London.
Hail
No hail was observed in this part of South London.
Snow
None reported.
Wind
Moderate or fresh southwesterlies blew for much of the first week, but from the 9th until the 20th gentle or moderate northeasterlies prevailed. Winds were light or gentle during the last 10 days of the month, mostly from between southwest and northwest. The highest gust during September was 30 knots (34mph) from the southwest on the 3rd.
Fog
None reported in this part of London.
Monthly figures for September in, and around, London
The average maximum temperature during September 2009 was 20.0 Celsius (68F), and that was 0.1 Celsius (0.2F) above the 20-year normal, but 0.9 degrees Celsius (1.7F) above the 100-year normal. The average minimum temperature was 11.4 Celsius (52F), and that was 0.4 Celsius (0.8F) above the 20-year average, and 0.8 Celsius above the 100-year normal.
The highest temperature recorded during September was 27.2 Celsius (81F) on the 8th, but the next warmest day was the 19th with only 23.6 Celsius (75F). However, there were a further 13 days, distributed fairly evenly through the month, when maxima were between 20 and 22 Celsius (68-72F). On most other days the top temperatures were between 18 and 20 Celsius (64-68F), but on the 15th the high was only 15.7 Celsius (60F), the coolest day of the month.
There was only 1 warm night during September, the 7th/8th with a minimum of 17.1 Celsius (63F). The next warmest night was that of the 22nd/23rd with a low of 14.8 Celsius (59F). There were 5 other nights when the temperature failed to dip below 14 Celsius (57F). On 8 nights the temperature fell below 10 Celsius (50F), with 6 of these chilly nights occurring during the last week. On 3 nights the minimum was below 7 Celsius (45F): the 17th/18th, 25th/26th and on the following night, which was the coldest of the month, with a low of 6.0 Celsius (43F).
Frost
There were no air or grass frosts during September. A grass minimum of 2.5 Celsius (37F) occurred on the night of the 26th/27th with 5 other nights, including 3 during the last week, when the grass reading was below 5 Celsius (41F).
Rain
A total of 23.6 millimetres (0.9ins) of rain fell during September, and that was only around 40% of average. Measurable rain only fell on 4 days, 8 below average, and remarkably there were only 2 wet days (1.0mm/0.04 ins, or more) and that was 7 days below average. The wettest day was the 15th with 12.9 millimetres (0.5 ins) and the only other wet day was the 2nd with 9.6 millimetres (0.4 ins). No measurable rain fell after the 15th.
Thunderstorms
For the 3rd consecutive September no thunderstorms were observed in this part of London.
Hail
No hail was observed in this part of South London.
Snow
None reported.
Wind
Moderate or fresh southwesterlies blew for much of the first week, but from the 9th until the 20th gentle or moderate northeasterlies prevailed. Winds were light or gentle during the last 10 days of the month, mostly from between southwest and northwest. The highest gust during September was 30 knots (34mph) from the southwest on the 3rd.
Fog
None reported in this part of London.
Monthly figures for September in, and around, London
| Place | Maximum | Minimum | Rainfall (mm) |
| C. London | 28.4 | 10.9 | 43 |
| Heathrow A/P | 28.1 | 8.2 | 36 |
| Gatwick A/P | 26.7 | 4.3 | 29 |
| Croydon | 25.4 | 6.7 | 25 |
| Northolt | 27.5 | 5.8 | 26 |
| Farnborough | 26.0 | 4.2 | 83 |
| Stansted A/P | 27.6 | 5.8 | 23 |