Temperatures, rainfall and sunshine were all close to normal in September.

Although the second half of September contained the warmest day of the month (22^nd with a maximum temperature of 23.6°C) the mean daily maximum temperature for 16^th/31^st was 3.1°C lower than for 1^st/15^th. The equivalent difference for night minimum temperatures was less pronounced, however, at 1.3°C.

The mean daily maximum temperature in September was 18.8°C, which is 0.2°C below the 30 Year (1976/2005) average. The mean night minimum temperature was 0.1°C below average at 10.7°C. Overall it was the coolest September since 2008 only.

The lowest night minimum temperature recorded in the month was 4.7°C on 25^th. The lowest grass minimum temperature of the month, 2.7°C, was also recorded on this date. The lowest daily maximum temperature in September was 12.9°C on 24^th, this coming surprisingly only 2 days after the warmest day of the month on 22^nd, as mentioned above. The highest night minimum temperature in September was 15.5°C on 11^th.

The mean earth temperature at 30 cms depth as recorded at 0900 GMT daily was 15.4°C. This element varied from a maximum of 16.8°C on 11^th to a minimum of 13.5°C on 26^th.

September commenced on a dry note with no measurable rainfall being recorded over the first 5 days of the month. A further relatively dry spell occurred from 11^th to 22^nd inclusive during which only 3.7 millimetres rainfall was measured.

The wettest day of the month occurred on 29^th with 12.6 millimetres rainfall and this amount enabled the monthly rainfall total of 53.8 millimetres to be only 6% below the 30 Year (1971/2000) average. Despite the marginally below average rainfall it was the wettest September since 2005, however.

The number of "rain days" (0.2 millimetres or more) in September was 17, whilst on 9 of these days rainfall exceeded 1.0 millimetre.

Total rainfall for the period January/September 2010 was 451.6 millimetres, which is 107% of normal. This excess has been achieved despite 7 of the 9 months so far this year having below average rainfall, the exceptions being the wet February and the exceptionally wet August.

A very sunny start to September was experienced with 33.5 hours sunshine being recorded over the first 3 days of the month. The 1^st with 12.4 hours sunshine was the sunniest day of the month and also the sunniest September day since at least 1997 (although it was only 1 minute ahead of 4^th September 2004).

The rest of the month was rather dull at times and the September sunshine total of 130.4 hours was 8% below the 1971/2000 average. However, only 1 day (27^th) in the month was completely sunless, although 19^th, 26^th and 29^th could only manage 1 minute of sunshine each.

September was a rather breezy month at times and the mean wind speed throughout the month was 5.9 mph. The maximum wind gust speed recorded in the month was 36 mph on 15^th. The highest daily (00/00 GMT) mean wind speed in September was 12.3 mph on 14^th, whilst the lowest daily mean wind speed was 1.5 mph on 2^nd.

Wind directions with southerly or westerly components accounted for all but 4 days in the month, as shown in the following table of wind directions at 0900 GMT daily: NORTH 2 days, NE 2, E 0, SE 3, S 6, SW 6, W 6, NW 5 and CALM 0.

The mean MSL air pressure in September was 1014.0 mB, which is 2.5 mB below the 30 Year (1976/2005) average. The highest and lowest air pressure values recorded in the month were 1026.0 mB on 13^th and 999.0 mB on 7^th respectively.

Fog (visibilty < 1000 metres @ 0900 GMT) was observed on only 1 day (27^th) in September.

Met. Observer, Royston (Iceni) Weather Station

10^th October 2010