A flood alert is in place for the Lizard, Penryn, Falmouth, Truro, Ladock, Tresillian and Grampound.
Shortly after 5pm today (Wednesday), the environment Agency says that a band of heavy rain is expected later this evening and into Thursday morning.
Widespread totals of 20 to 30 mm can be expected, with localised higher totals possible.
The agency warns that as rivers are already high and the ground is very saturated, flooding is likely.
If you are heading out on the roads, keep up-to-date with the latest traffic info here.
The wet weather comes on the heels of torrential downpours in November, which caused widespread flooding and traffic chaos.
With the Met Office issuing an amber alert yesterday (Tuesday), the wet weather is set to continue into the weekend.
The amber weather warning, which aims to advise members of the public to "take extra care" and "be prepared," is valid from 6pm on Wednesday until Thursday at 3pm.
The warning from the Met Office reads: "An area of low pressure is likely to move north across the UK during Wednesday night and Thursday, bringing periods of heavy rain.
"The exact track of the low is still open to some doubt, but with saturated ground and following the rain of Wednesday morning, a further 20-40mm of rain is likely to run off leading to an increased risk of flooding across Cornwall and Devon.
"This warning will be kept under close review and the public are advised to monitor for updates."
Although dry weather is expected on Friday, there are indications that more heavy rain and strong winds could hit Cornwall over the weekend, particular on Saturday.