Author: Eric Gilbert

Monday followed the recent pattern of cool and cloudy days that saw the thermometer eventually rise to 15.7C, early in the afternoon at 14.10, limited by lack of sunshine being 3.4C below my 40-year average. The past night was also cool dipping to 9.6C at 00.49 in the early hours of Tuesday due to thickening cloud that arrived.

Tuesday revealed a dreary start to the new day as cloud and variable shower activity are moving towards our area thanks to the recent depression, still in the southern North Sea, that will bring a northwesterly breeze.

In the Weather Records by Month since 1984 section the September data and associated graphs have been updated and corrected. The mean September graph quite clearly shows the increase in the mean temperature for the month since 1984, a significant change since around 1997. The rainfall fall data and associated graph for September has shown a steady mean total for the past fifteen years, the exception being the major change in 2024.

September 2024 review

Two records broken for rainfall

Although the month got off to a very warm start, with a peak of 25.5C on the 1st, the temperatures dropped away on subsequent days.

On the 5th a large depression developed over the Continent that for three days plagued the UK with dark, dreary days with little solar and many hours of rain. A significant total of 26.8mm was logged on the 5th that fell over the previous twenty-four hours. The daytime temperatures were a degree or two below average due to the low, thick cloud.

Frequent thunder was heard on the 6th and in the early hours of the 8th.

We came under the influence of a low-pressure system to the northwest for the next four days that brought much cooler Arctic air from near Iceland, also windier weather. A maximum of 13.8C on the 12th was 5.3C below my 40-year average and the coldest day since 3rd May. The night that followed was very cold for September with the thermometer sinking to 1.0C, being a significant 7.7C below my 40-year average and the coldest night since 25th April. This low briefly produced a ground frost.

High pressure took control of our weather from the 16th that gave us seven dry days with the wind brisk from the northeast. There were many hours of strong sunshine that lifted the thermometer to 22.3C on the 19th, the warmest day since the 1st (25.5C).

As the anticyclone eased away over Scandinavia, during subsequent days, a depression began to take charge of our weather with thunderstorms arriving during the afternoon of the 20th, no thunder with only modest rainfall. However, in the early hours of the 21st a noisy thunderstorm arrived at 05.15 with very heavy rainfall. The daily rainfall amounted to 17.4mm.

A very slow-moving depression covered the country on the 22nd and 23rd producing a large quantity of rainfall with 35.4mm during the 24 hours up to the 08.00 on the 22nd and another 34.0mm to 08.00 on the 23rd. The monthly rainfall at that point exceeded the previous record set in 2006 when 131.9mm was logged for the whole month.

The new September rainfall record was broken again two days later as another 19.9mm daily precipitation was added up to 08.00 on the 26th.

Another depression settled itself right over our area at 06.15 on the 26th with a barometric pressure of 984.7mb, the lowest pressure since 28th March 2024, thus continuing the very unsettled weather.

The month ended with very cool days and nights with ground frost in the early hours of the 28th and 29th as the thermometer briefly dropped to a minimum of 2.2C on both nights, being 6.4C below my 40-year average. The maximum on the 29th was a significant 5.5C below my long-term average due to the persistent thick, low cloud that produced more rainfall.

The rainfall total for September was a record 221.4mm beating the previous high of 131.9mm set in 2006. The wettest day occurred on the 23rd with 43.4mm of precipitation. Not only was this total greater than the previous September record but it also broke the record for the wettest month in the year set in November 2002 with 203.5mm.

It was a cooler than average September being 0.4C below my 40-year average principally due to the numerous cool days, 22 during the month.

Thunder was observed on four days, namely 6th, 8th, 11th and 21st, with radiation fog observed in the River Og valley in the early morning, up to 08.00, on the 17th.

Sunday was another cool day due to the brisk southeasterly breeze and lack of sunshine. The thermometer only reached a maximum of 13.6C mid-afternoon at 14.36 before cloud built up again, being 5.5C below my 40-year average. The thicker cloud ahead of the depression produced the first spots of rain at 18.00 with more frequent and heavier rain after 19.00.

After two very cool nights with a minimum of 2.2C last night saw the thermometer drop away to 9.8C late evening at 20.47 before the thicker cloud and rain arrived when the thermometer did an about turn and began to rise to reach 14.0C at 08.00 Monday.

Monday dawned dull under thick low cloud and light drizzle falling. The depression is now slowly moving eastwards into the North Sea having dawdled over the UK yesterday.

The rainfall for the past twenty-four hours, to 08.00 Monday, amounted to 17.4mm taking the September rainfall total to 220.9C. This total is 350.6% of my 40-year September average or plus 157.9mm. This exceptional rainfall made it the wettest September since 2020 that brought 191.0mm and the previous record set for any month in the year when 219.1mm was recorded in January 2014.

Saturday was such an enjoyable day with many hours of sunshine. However, after a cold night with a minimum of 2.2C and a brisk westerly breeze, the thermometer struggled to reach 14.3C late in the afternoon at 16.25, this being 4.8C below my 40-year average. The clear skies initially overnight saw the thermometer once again drop to a minimum of 2.2C in the early hours at 02.51 on Sunday, after that increasing cloud saw the temperature rise to 5.1C by 08.00.

Sunday dawned with a very red sky in the east for a few minutes as the sunrise illuminated the thin high cloud, but no sunshine. The barometric pressure has started to fall as the next depression closes in.

Another depression is slowly making its way towards the UK that will see the cloud increase significantly during Sunday bringing rain, probably starting light in midafternoon. The centre of the low-pressure will be just off Cornwall by midnight, it is forecast, so a very wet night ahead as there are two weather fronts that will cross our area during the hours of darkness.

The question is, will the rainfall in the next twenty-four hours break my all time monthly rainfall record for any month, set in September 2014, it only needs an additional 15.7mm. The rain had reached the Lizard Peninsula by 09.15.

The rain and drizzle eventually ceased around midday on Friday with the afternoon brightening a little with weak sunshine. However, the cloud and rain for part of the day combined with a brisk wind from the northwest gusting 25mph meant a very cool day with wind chill and the thermometer only reaching 12.3C at 16.17 being a significant 6.8C below my 40-year average. It was the coolest day since 27th April – Autumn is upon us! During the late afternoon and certainly overnight the skies cleared allowing any warmth to dissipate into the atmosphere that saw the thermometer drop to just 2.2C at 07.12 on Saturday giving a ground frost. This low was 6.5C below my 40-year average and was the coldest night since the 13th September when just 1.0C was logged.

Another 2.5mm or rainfall fell yesterday morning that took the monthly rainfall total to 203.5mm making it the second wettest month in the near since my records began in 1984 and equalled the identical amount in November 2002.

Glorious sunshine greeted the start to Saturday, what a relief after so many full wet mornings. Today we will be under a temporary ridge of high pressure that will give us a dry day with many hours of sunshine. The barometric pressure has risen a very significant 26mb since 08.00 on Friday. However, on Sunday another Atlantic depression will be heading towards the UK bringing more cloud and rain later in the day.

Thursday brought us a bright, sunny start to the day but by mid-morning in began to cloud over and just before mid-day an extremely heavy and intense shower arrived that caused some flooding on some Marlborough roads for a brief period. The brighter morning saw the temperature climb to a maximum of 17.3C at 11.29 before falling back a little as the cloud and rain arrived. The wind as forecast, backed into the northwest just after midnight, heralding a cooler airstream that saw the thermometer steadily drop away to reach a minimum of 7.5C at 07.53. The maximum was 1.8C below my 40-year average and the minimum was 1.2C below my 40-year average.

Another 14.8mm of precipitation was recorded taking the monthly total to 201.0mm, which is 319% of my 40-year average for September making it the third wettest month in a year, not just September, since my records began in 1984, using the recognised Meteorological Office 5″ copper rain gauge.

Friday revealed another wet start to a day with steady rain driven on by a strong northeasterly breeze. The strong wind from the northwest is producing a wind chill this morning so that outside it feels more like 5C than 7.5C.

The two depressions will join force as the day progresses and migrate into the North Sea, but the cooler airstream on the strong northeasterly wind will continue throughout the day. The barometric pressure is rising strongly, up 12mb since 08.00 yesterday, that will see the rain depart our area, probably soon after midday and bring a brief, drier period over Saturday.