Forecasters have issued a 'yellow' weather warning for heavy rain and possible flooding across parts of Devon and Cornwall, including Exeter, for today.
The Met Office says the warning is in place from 12:45pm to 8pm, with heavy thundery downpours expected.
A spokesman said the public should be aware of the potential for some minor disruption due to surface water flooding.
A Chief forecaster at the Exeter-based office 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 office warns the public should therefore be aware of the risk of localised flooding. In particular surface water could lead to difficult driving conditions at times. Hail and lightning are likely to provide an additional hazard locally.