Weather in South London during May 2009
A dry month, the driest May for 11 years, with temperatures slightly above normal
Temperatures
The average maximum temperature was 18.3 Celsius (65F), and that was just 0.1 degree Celsius above the 20-year normal. The average minimum temperature was 8.9 Celsius (48F), and that was 0.2 Celsius (0.3F) above normal.
The highest temperature recorded during May was only 24.6 Celsius (76F), on the 31st, a value that had been exceeded in each of the last 15 Mays. The temperature failed to reached 20 Celsius (68F) until the 23rd, but apart from on the 26th and 27th, maxima remained above this value for the remainder of the month, including a high of 24.5 Celsius on the 24th. There were no particularly cool days during May, but on 3 days the temperature failed to reach 15 Celsius (59F). On the 4th, the maximum was only 13.1 Celsius (56F), and on the 13th it was only 0.2 Celsius less cool.
The minimum temperature on the night of the 27th/28th was 13.3 Celsius (56F), and there were 11 other nights when the minimum value stayed above 10 Celsius (50F) with nearly half of these nights occurring during the last week of May. There were only 2 nights when the temperature dipped below 5 Celsius (41F), the 3rd/4th with a low of 3.3 Celsius (38F), and the 9th/10th with a minimum of 3.8 Celsius (39F).
Frost
There were no air frosts during May, and there were only 2 grass frosts, and that's 2 fewer than average. A grass minimum of minus 2.3 Celsius (28F) occurred on the night of the 3rd/4th with the night of the 9th/10th being the only other night with a grass frost.
Rain
A total of 28.9 millimetres (1.1ins) of rain fell during May, and that was nearly 40% below the long-term average. Measurable rain fell on 13 days, 2 days above average, but with the 5 wet days (1.0mm/0.04 ins, or more) 3 days below average. The wettest spell occurred around the middle of the month, but the 14th was the only day during this week of unsettled weather when rainfalll exceeded 5 millimetres (0.2 ins). The only other day when rainfall totalled more than 3 millimetres was the 25th. This was the wettest day of the month with 13.9 millimetres (0.55 ins) measured.
Thunderstorms
For the first time since 1996, no thunderstorms were observed during May..
Hail
None reported.
Snow
None reported.
Wind
Winds were generally gentle or moderate southwesterly, but during the third week they were fresh at times, and on both the 16th and 18th gusts of 31 knots (38mph) occurred. During the second week, winds were moderate or fresh northeasterly for a while, and during the last week northeast winds occurred, but these latter breezes were much warmer and accompanied by plenty of sunshine.
Fog
None reported.
Monthly figures for May in, and around, London
The average maximum temperature was 18.3 Celsius (65F), and that was just 0.1 degree Celsius above the 20-year normal. The average minimum temperature was 8.9 Celsius (48F), and that was 0.2 Celsius (0.3F) above normal.
The highest temperature recorded during May was only 24.6 Celsius (76F), on the 31st, a value that had been exceeded in each of the last 15 Mays. The temperature failed to reached 20 Celsius (68F) until the 23rd, but apart from on the 26th and 27th, maxima remained above this value for the remainder of the month, including a high of 24.5 Celsius on the 24th. There were no particularly cool days during May, but on 3 days the temperature failed to reach 15 Celsius (59F). On the 4th, the maximum was only 13.1 Celsius (56F), and on the 13th it was only 0.2 Celsius less cool.
The minimum temperature on the night of the 27th/28th was 13.3 Celsius (56F), and there were 11 other nights when the minimum value stayed above 10 Celsius (50F) with nearly half of these nights occurring during the last week of May. There were only 2 nights when the temperature dipped below 5 Celsius (41F), the 3rd/4th with a low of 3.3 Celsius (38F), and the 9th/10th with a minimum of 3.8 Celsius (39F).
Frost
There were no air frosts during May, and there were only 2 grass frosts, and that's 2 fewer than average. A grass minimum of minus 2.3 Celsius (28F) occurred on the night of the 3rd/4th with the night of the 9th/10th being the only other night with a grass frost.
Rain
A total of 28.9 millimetres (1.1ins) of rain fell during May, and that was nearly 40% below the long-term average. Measurable rain fell on 13 days, 2 days above average, but with the 5 wet days (1.0mm/0.04 ins, or more) 3 days below average. The wettest spell occurred around the middle of the month, but the 14th was the only day during this week of unsettled weather when rainfalll exceeded 5 millimetres (0.2 ins). The only other day when rainfall totalled more than 3 millimetres was the 25th. This was the wettest day of the month with 13.9 millimetres (0.55 ins) measured.
Thunderstorms
For the first time since 1996, no thunderstorms were observed during May..
Hail
None reported.
Snow
None reported.
Wind
Winds were generally gentle or moderate southwesterly, but during the third week they were fresh at times, and on both the 16th and 18th gusts of 31 knots (38mph) occurred. During the second week, winds were moderate or fresh northeasterly for a while, and during the last week northeast winds occurred, but these latter breezes were much warmer and accompanied by plenty of sunshine.
Fog
None reported.
Monthly figures for May in, and around, London
| Place | Maximum | Minimum | Rainfall (mm) |
| C. London | 25.9 | 7.5 | 27 |
| Heathrow A/P | 25.6 | 4.9 | 29 |
| Gatwick A/P | 23.9 | 0.4 | 74 |
| Croydon | 22.5 | 3.1 | 49 |
| Northolt | 25.2 | 2.2 | 32 |
| Farnborough | 24.5 | 1.1 | 53 |
| Stansted A/P | 23.3 | 1.7 | 25 |