After the record breaking warm first third of September, the weather has recently become somewhat more autumnal, with temperatures much closer to the long-term normal. Generally this is set to remain the case over the coming week or two. However, during the weekend we will see a very brief incursion of southerly winds, bringing above average temperatures to England and Wales, though the southerlies will not sustain for long enough to bring warm weather to Scotland or Northern Ireland. There will be widespread thundery activity for the second weekend in succession. As we head into next week, an unsettled, autumnal westerly type will set in, with temperatures again falling close to the long-term normal, and it has potential to become very windy at times.
Some rain will continue to spread northwards through the West Country during the morning, tending to become lighter and more showery as it moves northwards. It looks unlikely that there will be any further thundery activity associated with this, with the embedded thunderstorms having fizzled out overnight. The rain will spread into south Wales by midday and continue into the afternoon.
The warm southerlies will not make it into Scotland, Northern Ireland or northern England, where in most places it will be rather cool for the time of year. There will be plenty of sunshine and just a few scattered light showers in north-west Scotland, but otherwise it will start off cloudy, with a band of persistent rain affecting southern Scotland and some light rain affecting the north-east coast of England also. As the day progresses, the rain band will slowly fizzle out, and the brighter weather in north-west Scotland will spread southwards to cover the northern half of Scotland generally. Some sunshine will also come through in north-west England, although south-east Scotland and north-east England, especially near the east coast where there will be an onshore wind, are likely to stay grey and drizzly. Temperatures will generally be on the cool side for mid-September, with highs generally between 13 and 15C.
In stark contrast, from south Yorkshire and south Lancashire southwards, it will be a very warm day with plenty of sunshine away from the south-west, and temperatures will widely reach the mid to high 20s Celsius in central and eastern England, reaching around 27 or 28C in inland parts of the south-east.
The enhanced north-south split in temperatures will continue early on Sunday with temperatures dropping to between 3 and 6C in northern Scotland, giving potential for frost in the frost hollows, while most of southern Scotland, Northern Ireland and northern England can expect lows of around 10C. It will be a warm and sticky night for the south and east of England, with parts of the south-east not falling any lower than 16C.
As southerly winds set in across Scotland, the band of cloud and patchy light rain and drizzle over northern England and southern Scotland will push northwards through Scotland during Sunday. There will be some brighter weather to the south of it, with a rather warm and humid feel, before bands of heavy rain push in from the south. These will reach southern England during the morning, with potential for substantial thundery activity, particularly in south-west England and along the English Channel coast further east. They will continue to push northwards through the rest of England and through Wales during the afternoon and evening. Although the thunderstorms associated with them will tend to fizzle for a time, they may pep up again in the Midlands and northern England during the evening. Temperatures will remain above average in England and Wales, though it will be less warm in the south, with highs generally between 20 and 23C in most parts of England. However, most of Scotland and Northern Ireland will see highs of around 16C, and Northern Ireland will be dull and wet for most of the day.
On Monday, the warmer weather will become mainly confined to the south-east, with highs of around 23C in East Anglia and the south-east, as cooler fresher weather moves in from the west.
Further rain will spread from west to east during the morning, with potential for more thunderstorms in Wales, western England and along the English Channel coast. Brighter, showery weather will follow from the west. Tuesday looks set to be bright and showery in the north, with cloudier weather and persistent rain spreading across the south. Further wet weather will spread through the country on Wednesday, with potential for further thunder in England and Wales, though thunder is unlikely to be as widespread as through Sunday and Monday, and it will be warm and humid in eastern England. From Monday to Wednesday, it will also generally be windy. It looks likely to turn cooler with sunshine and showers at the end of the week.