Scattered heavy showers, hail and thunderstorms are likely to break out across southern parts of Cornwall and Devon early this afternoon.
The Met Office is warning the public to be aware of the risk of localised flooding and surface water leading to difficult driving conditions at times.
Adding that hail and lightning are likely to provide an additional hazard.
The Met office chief forecaster said: "A deeply unstable airmass covers much of southern England. As daytime heating gets going, we can expect showers and thunderstorms to break out and to be slow-moving at times, given light winds. 10-15 mm of rain will occur in less than an hour in places with some 25 mm possible in 3 hours or less. As is usual with these situations, some places will miss the worst of the rain.
The rain is expected to die out this evening.
Despite a weather warning yesterday, most of Devon and Cornwall escaped the downpours, however firefighters were called to Duloe, Liskeard just after 3pm after an isolated thunder storm flooded homes.
An appliance from Liskeard Fire Station was called out, with crews using a light portable pump and buckets and brushes to help owners with clearing flood water.
A crew from Looe Fire Station were also called to a transformer on a pole that was well alight. The crew assisted Western Power by using a hosereel for fire cover, when the fire as under control the incident was left in the hands of Western Power.