A warning of heavy rain has been issued for Cornwall from 4pm today.
The Met Office has put the yellow-graded weather warning, the lowest of its kind, in place from 4pm today until 3am on Wednesday.
Forecasters warn of heavy showers, including heavy hailstorms, throughout the evening and into the early hours.
A chief forecaster at the Exeter-based Met Office said surface water flooding issues are likely.
He said: “A showery west to northwesterly airstream covers southern Britain at present. An active band of showers is expected during the evening, dying out during the early hours of Wednesday.
“Although the amounts of rain will not be excessive (typically 10-15mm, perhaps locally around 25mm over the moors), some of the showers could be quite intense and given the wetness of the countryside, a few localised surface water flooding issues seem likely.”