Tag: September

September 2011 was the warmest for four years and the fourth warmest September I have recorded. The mean temperature of 15.0°C was 1.2°C above the long-term average. The month ended with a mini-heat wave when the thermometer peaked at 26.6°C on the 29^th and just lower than this on the following day with 26.4°C. This was brought about by a large high pressure area to the east of us allowing very warm and dry air to flow north from the Mediterranean. This system became a blocking high stopping weather fronts from making progress from the Atlantic. A record was set for this station on the 10^th when the minimum temperature was a very warm 16.4°C., which was warmer than three of the day time temperatures in the month. It was also a relatively dry month; the total of 46.9mm was 74% of the long-term average. After a warm start for the first two days we had nine successive days of rainfall, but no great daily totals. The wettest day was the 18^th with 8.1mm.

September was an unusual month.  I cannot remember when the mean temperatures and total rainfall were almost identical to the long-term averages. The mean maximum was identical at 18.7°C and the mean minimum just 0.2°C below. The total rainfall was 63.0mm compared with the long-term average of 63.6mm. The first 12 days often brought days with glorious sunshine, light breezes and above average maxima with a maximum of 22.6°C on the 10^th. With winds veering into a more northerly direction in the middle of the month there were some very cool nights with a minimum of 2.6°C in the early hours of the 18^th. The wettest day was the 22^nd with 16.9mm. The latter part of September brought depressed maxima combined with windy and wet days.

September has been such a contrast to previous months. A mild first eight days, with the wettest day of the month on the 3^rd (8.3mm) changed when the jet stream at last moved north allowing pressure to build. The downside was the arrival of strong northeasterly winds, a maximum gust of 31mph occurred on the 16^th, which were unpleasant and lasted until the 19^th.  A light shower was noted on the 22^nd and 23^rd with the remainder of the month being warm and dry with very pleasant autumn sunshine.

The average temperature was 0.2° above the long-term average with no air frosts but a minimum of 2.7°C on the morning of the 27th. This was the driest September I have recorded and is identical to September 2003, which also had a total of 11.1mm and is just 17% of the long-term average. The figure for evapotranspiration, the amount of moisture that evaporates form the ground and plant life, was 59.2mm and explains why the ground is now so dry after a wet summer.