Britain could experience temperatures climbing as high as 25C by the end of the week, according to the latest Met Office forecast, offering hope of respite from the “relentless” low-pressure systems that have dominated September weather.
The UK weather agency has indicated there could be a “shift on the horizon” with warmer and drier conditions potentially arriving from Friday, 19 September, as a ridge of high pressure builds to the west of the country. However, before any improvement, persistent rain and strong winds are forecast to batter much of the UK throughout the week.
The Met Office has issued two yellow weather warnings for rain across Wales on Wednesday, with some areas expected to receive up to 50mm of rainfall in just six hours, particularly over higher ground.
Heavy Rain to Hit Central Areas
Wednesday, 17 September, is expected to start with a band of heavy rain sweeping across the UK, with the Met Office warning that the heaviest rainfall will affect central areas. Wales appears particularly vulnerable to intense downpours, prompting the weather agency to issue specific warnings.
The first yellow weather warning covers parts of north-west Wales between 3am and 12pm on Wednesday. A second warning has been issued for south and south-west Wales, running from midnight until 11pm. Both warnings highlight the risk of localised flooding and travel disruption.
“Wednesday starts with a band of heavy rain sweeping across the UK,” the Met Office explained. “The heaviest rainfall is expected across central areas, with Wales, particularly the south and west, prone to intense downpours. Some locations could see up to 50mm of rain in just six hours, especially over higher ground.”
Thursday’s Lingering Weather Front
On Thursday, 18 September, the weather front moves through but leaves a trailing system across central parts of the UK. The Met Office forecasts that wet weather is likely to persist for the Midlands and Wales, possibly extending into the south-west of England.
There remains some uncertainty about the exact position of this rain band, but forecasters expect it will “ebb and flow through the day, occasionally pushing northwards.” Northern England may see drier and brighter intervals between rain bands and showers affecting northern Scotland.
The far south and south-east are most likely to stay dry on Thursday, though gusty winds will persist across much of the country. The strongest winds will be confined to northern Scotland, where coastal gales could bring gusts of 50mph or more.
Friday’s Potential Warmth
From Friday, 19 September, weather conditions are set to undergo a significant shift as temperatures could climb as high as 25C, depending on wind direction. The Met Office has identified a change in the jet stream pattern as the key factor behind this potential transformation.
“Despite the ongoing unsettled conditions, there are encouraging signs of change,” the Met Office stated. “A ridge of high pressure is building to the west of the UK, and as the jet stream shifts, this high pressure is expected to move across the country during the final week of September.”
Heavy rain is still expected on Friday in Wales, northern England, south-west Scotland, and Northern Ireland. However, the south is forecast to turn drier and brighter, with the best of the sunshine expected in the south-east.
London Could See 25C
Winds will begin to change direction on Friday, potentially bringing warmer air to London and the south-east. The Met Office explained that temperatures in these areas could climb to 23C or even 25C, depending on wind orientation.
“This transition could bring an end to the relentless cycle of low-pressure systems, offering a drier interlude and a welcome break from the wet and windy weather that has dominated so far,” forecasters said.
The potential for higher temperatures is linked to changes in the jet stream, which has been driving successive low-pressure systems towards the UK from the North Atlantic.
Understanding the Jet Stream Changes
The Met Office has provided detailed analysis of the atmospheric patterns driving the UK’s changeable weather. “To understand the evolving weather, it’s helpful to look at the jet stream setup,” they explained.
“On Tuesday, the jet stream is relatively flat across the North Atlantic, driving a succession of low-pressure systems towards the UK. Over the next few days, subtle changes occur, with the jet stream becoming more amplified as it crosses the Atlantic.”
This amplification sees one portion of the jet stream dipping south whilst another pushes north over the UK. This shift has several impacts, including allowing warmer air to move into the south-east on Friday and Saturday, raising the chance of thunderstorms as the warmth builds.
Weekend Outlook
The warmer conditions in the south-east could persist into Saturday, though forecasters warn that the increased warmth raises the possibility of thunderstorms developing. The jet stream changes will also push the wettest weather towards the north-west as the weekend begins.
“Within the trough of the jet stream, heavy rain and showers are likely to develop, especially as the system slowly crosses the UK during the weekend and into the start of next week,” the Met Office stated.
Despite the rain continuing in some areas, northern England is expected to see brighter spells developing by Wednesday afternoon, whilst the north Midlands and north Wales may also experience some improvement.
Autumn Pattern Continues
The current unsettled conditions are typical for September as the UK transitions into meteorological autumn. The Met Office notes that whilst some bright spells can be expected between the rain, particularly in northern England, the overall pattern remains dominated by Atlantic weather systems.
Looking ahead to the final week of September, forecasters suggest that if the high-pressure ridge successfully establishes itself across the UK, it could herald a more prolonged period of settled weather. This would mark a significant change from the wet and windy conditions that have characterised much of September so far.
Travel Disruption Expected
With the yellow weather warnings in place for Wednesday, the Met Office is advising people to check travel conditions before setting out. The combination of heavy rain and strong winds could lead to difficult driving conditions, particularly on exposed routes and bridges.
Public transport may also face delays, with the potential for localised flooding affecting road and rail networks. The Environment Agency and Natural Resources Wales are monitoring river levels closely, with flood alerts possible in vulnerable areas.
Climate Context
The potential temperature swing from heavy rain to 25C warmth within days highlights the increasingly variable nature of UK weather patterns. The Met Office notes that whilst September can deliver warm spells, the rapid transitions between weather types are becoming more pronounced.
Summer 2025 was confirmed as the warmest on record for the UK, with a mean temperature of 16.10C, surpassing the previous record set in 2018. This context makes the potential for late September warmth less surprising, though the contrast with the week’s earlier conditions remains stark.
As Britain navigates another week of changeable autumn weather, the prospect of warmer, drier conditions by week’s end offers hope for those weary of the persistent rain. Whether temperatures reach the predicted 25C remains to be seen, but the Met Office’s identification of a “shift on the horizon” suggests that relief from the current unsettled pattern may finally be approaching.
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