As we move into September, the UK’s weather is living up to expectations for an unsettled autumnal start.
The latest Met Office 10-day trend highlights a period dominated by low pressure, frequent showers, and the risk of heavy downpours and strong winds. While there are brief interludes of drier and brighter weather, the overall theme is one of continued volatility, with little sign of prolonged settled conditions on the horizon.
A look at the current setup
At present, the UK is under the influence of a broad area of low pressure. This has brought widespread heavy, showery rain, with some locations even experiencing rumbles of thunder. The low is now beginning to clear away towards the north, but the respite will be short-lived. An occluded front is pushing in from the southwest, set to bring further rain to parts of England and Wales as we move through Thursday. This front will be the focus for some particularly heavy and thundery showers, especially along a line from South Wales through the Midlands and up towards the Humber.
Warnings for heavy rain and flash flooding
The risk of intense downpours is significant enough for weather warnings to be in place. Some areas could see 30 to 60 millimetres of rain in just an hour, which is enough to cause flash flooding in a few places. Even outside the warning area, showers will be widespread and could be heavy at times. However, there will also be some bright or sunny spells in between, and as Thursday progresses, showers are expected to ease for many.
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A brief drier spell on Friday
As we head into Friday, the weather is set to turn a little drier for many. The influence of low pressure will diminish, and an area of higher pressure will start to build from the south. This will help to settle conditions, albeit only temporarily. Friday is expected to be largely fine, though not completely dry. There may be a few showers, particularly across western areas during the morning, but for most, it will be a day of dry and often sunny weather. Some cloud may bubble up in the afternoon, bringing the odd shower, but overall, Friday looks to be the driest day of the week for most.
Weekend outlook: a tale of two halves
The weekend brings a shift in focus as attention turns to developments across the Atlantic. A new area of low pressure is heading towards the UK, and the atmospheric setup is particularly interesting. There is a double jet stream configuration, with a more southerly jet initially driving the incoming low, but a more northerly jet is also present. This northerly jet is expected to be influenced by an upper trough, causing it to extend further south and eventually merge with the southern jet. The combined effect will be to strengthen the approaching low pressure system as it heads towards the UK.
Saturday is likely to start on a relatively fine note for many, with high pressure to the east and low pressure still out to the west. Most places will enjoy a good deal of dry weather, perhaps with some high-level cloud making the sunshine a little hazy at times. However, as the day progresses, it will turn wetter and windier across the far west.
Sunday: the wettest and windiest day
It is not until Sunday that the full impact of the deepening low pressure system will be felt. This system will throw its fronts across the country, bringing a return to more unsettled weather. Sunday is expected to be the wettest and windiest day of the weekend, with widespread rain and the potential for strong winds. Although relatively warm air will be drawn in, cloud and rain will limit the rise in temperatures. While on paper, temperatures could reach the mid to high 20s Celsius, this is considered unlikely. Most places will see highs in the low 20s at best.
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The low pressure system is expected to be quite deep, with central pressures potentially dropping to around 975 to 980 hPa. This raises the risk of strong winds, particularly in exposed areas, and further heavy rain. Rainfall totals for Sunday could reach 10 to 30 millimetres widely, with some locations possibly seeing 50 to 60 millimetres. There remains some uncertainty about the exact timing and location of the heaviest rain, so forecasts should be monitored closely.
Into next week: unsettled conditions persist
As we move into Monday, the UK will still be under the influence of the same low pressure centre, which is likely to be at its deepest late Sunday into Monday. This means the working week will start on an unsettled note, with further heavy rain and strong winds possible. The overall story remains one of unsettled weather, and this theme is set to continue through much of the week.
Looking at the most likely scenarios for Tuesday, all suggest a similar pattern: low pressure remains in charge, though its exact position may vary. The most probable setup has the low shifting slightly northwest, but other scenarios keep it closer to the UK, which would mean another wet and windy day. Even if the low is a little further away, the unsettled theme will persist.
Rainfall patterns and regional differences
The position of the low pressure system, generally to the northwest of the UK, means that the heaviest rain and strongest winds are expected across western parts of the country. Further east, there is a greater chance of staying dry, but even here, some wet weather is likely to push through at times. The blues on rainfall charts indicate areas where it will be wetter than the seasonal average, but this does not mean other areas will be dry, just less wet by comparison.
Mid to late week: little sign of lasting improvement
As we move through Wednesday, Thursday, and Friday, the unsettled theme continues. The most likely scenario for Wednesday is that the low pressure system edges closer to the UK, bringing another wet day. The second and third most likely scenarios are similar, all involving low pressure somewhere to the north, northwest, or west of the UK. Some model runs suggest the low may begin to drift away by Friday, but many keep it nearby, maintaining the unsettled pattern.
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The search for higher pressure: a recurring theme
One tool often used by forecasters is the probabilistic pressure trend chart. Last week’s 10-day trend hinted at the possibility of higher pressure returning around the 7th or 8th of September. However, more recent model runs have made this outcome look less likely. The reds on the pressure charts, indicating higher pressure, have become less intense, suggesting that any return to settled weather is being pushed further into the future.
This is a familiar pattern at this time of year. Forecasters often talk about the “6 to 10 day ridge”, a ridge of high pressure that appears in model runs but always seems to be about 10 days away and keeps getting pushed back. In this instance, it may never actually materialise. While there may be a slight reduction in the intensity of unsettled weather towards the end of the period, there is little confidence in a significant or lasting improvement.
Temperatures and winds: what to expect
Throughout the period, temperatures are expected to be around average, perhaps a little below at times, especially during spells of unsettled weather. Strong winds and coastal gales are possible, particularly when low pressure is at its deepest. While there will be some drier spells, Friday and Saturday, for example, look largely dry for many, these will be the exception rather than the rule.
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