The headline for September 2024 has to be the huge amount of rain. There was significant flooding for parts of England and Wales with ten English counties witnessing their wettest September on record.
“For Bedfordshire and Oxfordshire, September 2024 was the wettest calendar month the counties have experienced, in a series dating back to 1836. “ Met Office
Some counties recorded more than three times their average September rainfall; Bedfordshire, Berkshire, Buckinghamshire, Gloucestershire, Northamptonshire, Oxfordshire and Wiltshire.
The heaviest rain was confined to the latter part of the month with drier spells mid-month. Overall no national monthly records were broken and it wasn’t wet for everyone. 114.1mm of rainfall was recorded across the month but the UK’s highest September rainfall total was 178.5mm, recorded in 1950.
It has been southern and central England seeing the real soaking. The colour scale had to be extended from the usual blues to accommodate the high rainfall values.
“Southern England had its wettest September since 1918, and its third wettest on record in a series from 1836.” MO
However, Scotland and Northern Ireland have been drier than average. Comparing to the rainfall averages in the 30-year period 1990 to 2020, this October saw 125% of the long-term meteorological rainfall average across the UK as a whole, one quarter more. England saw about double, 195% of the average rainfall. Scotland 63% so drier here, Northern Ireland 82% and Wales 139%
The jetstream had shifted southwards with several low pressures running in off the Atlantic bringing more and more rain to southern Britain. Further north it wasn’t as wet. Heavy showers and thunderstorms also brought torrential downpours which resulted in surface water flooding.
With low pressures coming and going the airflow would change. Sometimes with a cool NW/N or NE wind set in, other times a milder southerly. Horsham in West Sussex saw the highest September temperature with 30C on the 1st. Strathclyde and County Down both reached 27C on the 6th. There were some cold nights, the 13th and 25th when temperatures fell below zero in some rural areas.
Overall for the UK, September was about average temperature-wise just 0.3°C below the long-term meteorological average for the month. Northern Britain and Northern Ireland were slightly cooler than average and East Anglia was slightly warmer than average.
Much of Wales and England was duller than average along with all the rainfall. The western half of Scotland and Northern Ireland were sunnier than average.
National Highways, which maintains the dual carriageway, said it had already removed more than 24 million litres (5.3 million gallons) of water from the road, enough to fill 10 Olympic-sized swimming pools. However, it said continued rainfall and run-off from surrounding areas was making the situation "extremely challenging". BBC News
The relentless rain episodes over England and Wales in the later part of the month led to Amber and Yellow rain warnings, and numerous flood warnings from the Environment Agency as river levels rose and road flooding occurred. The A421 in Bedfordshire had to be closed on 22nd September after a month's worth of rain fell in two days.
“As our atmosphere warms it can hold more moisture, roughly 7% more per 1°C of warming. This can lead to more intense and frequent downpours. In autumn, the UK will likely see more days with rainfall totals over 50mm, particularly for western areas of the UK. It is important to note that there are other factors that contribute to flooding, such as land use, local hydrology and preceding conditions.” Met Office
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