The remnants of a hurricane thousands of miles away may help shape the UK’s weather this weekend.
The connection involves tropical thunderstorms, changes in the jet stream and a weather front whose development remains unusually uncertain.
Before looking ahead, it is worth reflecting on the exceptional warmth experienced across the UK at the end of September. Temperatures reached 28.1°C at Kew Gardens on Tuesday, placing conditions towards the upper end of what would normally be expected at this point in the year. Although not record-breaking, the warmth was notable both by day and overnight, with minimum temperatures of 18°C or 19°C possible in places.
The warmth is being drawn northwards ahead of a large area of low pressure to the west of Ireland. This low is pushing the jet stream to the south while bringing unusually warm air across the UK. Cloud, rain and strong winds are preventing the air mass from reaching its full temperature potential, but conditions are still well above average across much of England and Wales.
A change to showers
A cold front moving eastwards marks the beginning of a transition. Heavy rain is expected across western Britain and Northern Ireland, with 20 to 30mm possible in several locations and perhaps 50 to 60mm over some western hills. A narrow zone of particularly heavy rain and gusty winds is also possible along the front.
As the front moves east on Wednesday, it is expected to weaken, meaning eastern and south-eastern England will see less persistent rain than areas farther west. Behind it, the jet stream is forecast to move south across the UK and introduce a returning polar maritime air mass. This air begins in polar regions but follows a long path over the Atlantic, gathering moisture and becoming increasingly unstable.
READ MORE: Weekly weather quiz September 28: Test your knowledge!
The result is a mixture of sunshine and lively showers, particularly across southwestern England, Wales, Northern Ireland and western Scotland. Some showers could contain hail, thunder and heavy downpours, accompanied by gusty winds. Despite the changeable conditions, temperatures could still reach around 25°C in south-eastern England.
Further showers are expected on Thursday, initially with the potential for hail and thunder before gradually becoming less intense. Friday remains relatively mild, although temperatures begin to ease, with high teens or low 20s in the south and values in the mid-teens farther north. A brisk west-south-westerly wind will bring further showers, especially to northern and western areas.
Why Saturday’s forecast is uncertain
The main forecasting challenge concerns a frontal system approaching the UK on Saturday. One operational forecast shows the front producing persistent and sometimes heavy rain across Northern Ireland, southern Scotland, northern England and north Wales. However, this wetter outcome is in the minority among the range of available model solutions. Many ensemble members instead indicate a shorter spell of showery rain, followed by drier conditions.
The difference comes down to a relatively subtle feature high in the atmosphere. One model develops a sharper upper trough, or kink in the jet stream, to the west of the UK. Lower pressure at this level encourages air to rise from below, which can strengthen a weather front and intensify its rainfall. In that scenario, the front becomes more active as it crosses central parts of the UK.
Other models produce a weaker connection. Their upper trough is less pronounced, so the front brings more intermittent rain and showers rather than a prolonged wet spell. This is a useful reminder that a single forecast chart represents only one possible outcome. Comparing multiple model runs helps meteorologists identify which scenarios have stronger support and where uncertainty remains.
READ MORE: When is a hurricane not a hurricane?
From the Pacific to the Atlantic
The origin of this uncertainty can be traced back across the Atlantic and North America to the remnants of Hurricane Polo. As the former hurricane carries tropical moisture and thunderstorms into the central United States, condensation within those storms releases heat into the atmosphere. This is known as latent heat release.
That heat causes air to expand and rise through the troposphere. The resulting changes in pressure and airflow high above North America can strengthen the jet stream. Like a wave travelling downstream, that disturbance can then move towards the Atlantic, sharpen an upper trough and potentially intensify the front approaching the UK.
The models differ in how effectively they represent this sequence. The Met Office operational model transfers more energy from the former hurricane into the jet stream, creating a sharper trough and a wetter Saturday. Other solutions show a weaker interaction and therefore a less persistent spell of rain. The wetter scenario cannot be ruled out, but it currently has less support.
What happens next?
Any rain on Saturday is expected to ease, with higher pressure building from the south towards the end of the weekend and into early next week. Southern areas are therefore more likely to become settled, while northern parts of the UK may remain changeable as Atlantic systems pass farther north.
This forecast demonstrates how interconnected the atmosphere is. A former hurricane does not need to reach the UK to influence its weather. By altering the jet stream thousands of miles upstream, tropical weather over North America can contribute to uncertainty over whether the UK experiences persistent rain or a shorter, showery spell several days later.
Keep up to date with weather warnings, and you can find the latest forecast on our website, on YouTube, by following us on X and Facebook, as well as on our mobile app which is available for iPhone from the App store and for Android from the Google Play store.
