Parts of the UK could be lashed by rain and thunder after the last day of meteorological summer.
Forecasters said Thursday would be dry and fine for many but cloud will increase in southern England and Wales with some isolated showers developing into the afternoon.
These could be heavy and thundery in the south, according to the Met Office. Looking ahead to Friday, meteorologists say all early nebulae will clear.
Any early patches of fog and fog will dissipate. Then mostly dry and bright with scattered sunbeams, however there are large areas of cloud cover and a risk of showers which can be locally heavy and are most common in the north and west.
Saturday will be dry for most but there will be areas of heavy cloud cover and a chance of showers or rain showers, some of which may be heavy.
The Met Office issued a yellow weather warning for rain in Northern Ireland on Saturday. There is a “small chance” that houses and businesses would be flooded and some buildings would be damaged, it said.
Spray and flooding could also cause difficult driving conditions and some road closures. Areas of heavy rain are expected to pulse north through much of Northern Ireland and south-west Scotland through Saturday, possibly accompanied by thunderstorms.
In the worst-hit areas, 30-40mm of rain could fall in just two to three hours.
Sunday will be cloudy with cloudy skies and will bring rainfall which will mainly occur in northern and western areas.