The Met Office has issued a yellow warning for thunder storms across south west parts of Wales on Monday evening.
The warning comes into effect from 4pm on Monday, 7 October and runs until midnight.
Forecasters say that some places will miss the worst, but heavy showers and thunderstorms may cause some disruption, particularly to travel.
The warning says: "Areas of heavy showers and thunderstorms will move northwards across southern parts of England and Wales later Monday, clearing northwards overnight.
"Some places will see 20-30 mm of rain within 2-3 hours, with a small chance that a few places could receive 40 mm. Thunderstorms are most likely for south-facing coastal districts, and hail and some strong gusts of wind could accompany the heaviest showers and thunderstorms."
Some flooding is possible along with short term power loss.
Frank Saunders is a Chief Meteorologist at the Met Office and said: “Areas of heavy showers and thunderstorms will move northwards across southern parts of England and Wales later this afternoon before clearing northwards overnight.
“It’s possible that some places could see 20-30mm of rain within two to three hours, with a small chance that a few places could receive 40mm.
“Thunderstorms are most likely for south-facing coastal districts, and hail and some strong gusts of wind could accompany the heaviest showers and thunderstorms.”
Tuesday will be another day of sunshine and showers. Further heavy showers and thunderstorms are expected across central and southern areas of the UK, the areas affected perhaps overlapping those where heavy rain falls this evening. This overlap increases the chance of some surface water issues, particularly on roads. A longer period of heavy rain is also expected over parts of southeast Scotland and northeast England later on Tuesday through to Wednesday.
Further warnings are possible until mid-week as rain falls on already wet ground, but then the risk of flooding should reduce.
Ex-Hurricane Kirk
The Met Office says it has been keeping a close eye on the track of ex-Hurricane Kirk as it travels across the Atlantic.
They say: “There is increasing confidence now that it will track to the south of the UK, bringing heavy rains and strong winds to northern France. Although north and south shifts of the systems track remain possible, the threat of significant impacts to the UK from this system are now much reduced.”
Turning colder as the week progresses
The rest of the week continues to look unsettled, with rain and showers affecting most areas at times, but probably less heavy and less widespread overall.
Things also look to turn colder, with temperatures dipping from Wednesday in the north and all areas experiencing below average temperatures from Thursday. Night frosts are expected for some regions, and snow is possible for the higher mountains of Scotland.