Motorists are being warned to take extra care while driving on Wednesday evening with an inch of rain expected to fall in parts of Northern Ireland in just six hours.
Spray and flooding on roads could lead to difficult driving conditions and longer journey times.
The Met Office has issued a yellow severe weather warning across NI.
Only the western parts of counties Fermanagh and Londonderry are excluded from the warning.
A yellow weather warning has also been issued in the Republic of Ireland, where as much as 35mm of rain is expected tonight.
On Wednesday morning, motorists reported poor visibility on the Glenshane Pass, rain and low cloud hampering driving conditions.
The yellow warning remains in force until 20:00 BST on Wednesday.
But that isn't the end of the wet weather.
More heavy rain is due to move up the Irish Sea coast overnight affecting County Down and the east coast of County Antrim during the early hours of Thursday morning.