The Met Office has said that up to two inches of rain is expected to fall and two yellow weather warnings are in place for southwest England and northern Ireland until 9pm on Tuesday.
Over the next few hours heavy downpours will hit Somerset, Dorset, Cornwall, Devon and Northern Ireland.
From noon on Tuesday another yellow weather warning for thunderstorms is in place which will affect, London, Reading, Brighton, Portsmouth, St Albans, Cambridge, Ipswich and Norwich.
Met Office forecaster Amy Bokotan said: “The downpours could be slow moving, and that’s the main trouble – the wind’s quite light at the moment so when they do form, they could be quite slow moving and intense.
She added: “Where you see them they could be quite intense and dramatic, but not everywhere’s going to see them and some places just down the road could be completely fine and shower and thunderstorm-free.
