Thursday 1st October
Wednesday was another pleasant autumn day with both the maximum of 21.7C at 14.37 and the overnight minimum of 9.8C, several degrees above average. During the evening several lines of broken showers were observed passing to the west and east of Marlborough with a light shower arriving here at 22.15 and then just after 02.00, that totalled 1.6mm.
Thursday after first light revealed that radiation fog had begun to form in the River Og valley after 06.30, that had completely dispersed by 07.40 as the sun got to work. This coincided with the temperature falling to its lowest at 07.34, after sunrise in Marlborough at 07.07.
The barometric pressure is currently rising rapidly and forecast pressure charts indicate that it will dominate our weather up to the weekend and likely into next week, with the breeze coming from a direction between south and west. This will result in several days with sunny intervals and maximum temperatures well above the October average. There is little indication, at the moment, of any rainfall well ahead into next week.
September 2026 Review
After the heatwaves in August, it was a relief to start the new month with a little cooler air and a couple of days with modest welcome rainfall.
Sunday the 6th was memorable for a plume of very warm air that was pushed across from the near Continent on a southerly breeze that resulted in the thermometer climbing higher again with a maximum of 26.3C, being 7.3C above my September average.
Very welcome rain fell on the 8th totalling 10.1mm as a depression threw weather fronts across the country.
The second week brought variable weather, some dry days and others with minimal rain from a predominantly south-westerly airstream. The slight relocation of the high and low weather systems saw the wind vary from southwest, bringing warm and most air, to veering into the northwest, a cooler and drier airstream originating just south of Iceland.
The third week saw the breeze again vary between southwest and northwest with maximum temperatures close to the average and a modest rainfall of 2.8mm from several passing banks of drizzle and light rain on the 19th.
A significant area of high-pressure moved across the country on the 20th, which heralded a period of very warm, dry and sunny weather with maximum temperatures rising several degrees above the late September average with a peak of 23.7C on the 21st being 4.7C above my late September average.
The other significant feature of that week was the lack of air movement. For many continuous hours overnight, and often during the daytime, the anemometer was becalmed as the centre of the high pressure was almost overhead.
The last week was a topsy turvy week as almost daily the barometric pressure rose and fell as the recent anticyclone relocated and low-pressure systems tried to advance from the Atlantic.
A flow of cooler air and a cold front passing over the country on the 27th resulted in the coolest day of the month with a minimum of 17.3C, which was 1.7C below average. This was followed by a very warm and moist day on the 28th as a temporary flow of warmth was drawn in from Europe on a southeasterly breeze.
All the while the recent anticyclone, then over eastern Europe, acted as a buffer to the advancing depressions trying to advance from the Atlantic, that had by the 30th deepened significantly with a forecast barometric pressure of 955mb, centred south of Iceland. This resulted in the lowest barometric pressure here all month with a low of 1006.8mb.
The month ended with a significantly warm night when the thermometer did not drop below 17.8C, which was only just below the average maximum for September.
It was the second warmest September I have recorded with a mean temperature 2.3C above my long-term average, with the year 2023 being 0.4C warmer. The analysis reveals that the average maximum was +2.4C whist the average minimum was +2.2C, unusually even.
Looking back over my records, I note that for September, the average temperature has risen from 13.2C in the 1980s to 14.1C in recent years.
The rainfall of 28.8mm was just 43% of my 43-year record or minus 38.4mm. The wettest year since my station started in 1984 was 2024 with 221.4mm and the driest was jointly 2003 and 2009 with just 11.1mm.
The rainfall for the period January to September now stands at 489mm, which is surprisingly just 92mm below my 43-year average. The reason being the very wet January and February that allowed considerable water to percolate down to the aquifers with minimal evaporation. The contrasting year was in in 2022, when by that point in the year we had only received 336mm. The records show that only February in that year, for this period, had an above average monthly rainfall.