Wild apple tree at Swaines Green in September sunshine (Roger Emmens)
Another heat record broken in September
September certainly gave us variety.
The month started off largely settled and summery, with winds generally in a southerly sector, and on 15th we had our warmest September day on record (data covering 1979-2013), topping out at 31.2°C and comfortably beating the previous high of 28.9°C in 2013.
Towards the end of the month however it became a lot more autumnal, and a typical autumn depression moved through during 23rd-25th, with the cold north-westerlies behind it giving a daytime maximum of 11.6°C and a chilly night of 5.8°C on 26th.
This resulted in the second month in a row with an extreme difference between hottest and coolest temperatures, of 25.4°C - not as great as in August, but nonetheless impressive.
At least it wasn’t a wet month: the 30.2mm total was just over half the average, and rain fell on just nine days – only six out of the 36 years on record experienced fewer rainy days.
Below is the summary data for September 2020.
| Measure | Unit | Minimum | Average | Maximum | Average min | Average max | Total |
|---|---|---|---|---|---|---|---|
| Absolute humidity | g/kg | 4.4 | 8.4 | 13.7 | |||
| Relative humidity | % | 38 | 78 | 98 | |||
| Temperature | °C | 5.8 | 15.2 | 31.2 | 10.8 | 20.9 | |
| Wind source | ° | 4 | 214 | 359 | |||
| Wind direction | ° | 0 | 158 | 359 | |||
| Wind strength | mph | 0 | 3 | 19 | |||
| Rain daily accumulation | mm | 0.0 | 1.0 | 9.8 | 30.2 | ||
| Barometric pressure | mm | 994.3 | 1017.8 | 1030.9 | |||
| Solar irradiance | hPa | 0 | 121 | 914 | |||
| UV index | W/m² | 0.0 | 0.8 | 6 | |||
| Cloud base altitude | m | 35 | 525 | 2000 | |||
| Dew point | °C | 1.7 | 11.0 | 18.8 | |||
| Heat index | 16 | 25 | 48 | ||||
| Wind chill | °C | 3.7 | 15 | 32.8 |