Householders and businesses are bracing themselves for heavy rain with up to 40mm forecast along the east coast overnight.
Motorists have also been urged to take extra care driving in wet conditions, which are expected to worsen throughout the evening.
Met Eireann warned that a spell of heavy and possibly thundery rain will move in from the Irish Sea this evening and continue overnight.
"Totals of 25mm to 40mm are likely, with the highest totals expected over east and south Leinster," it added.
Meanwhile, AA Roadwatch advised motorists to reduce their speed in the rain.
It also urged drivers to keep a safe distance from the car in front and to use dipped headlights to improve visibility.
This coincides with a Garda crackdown on speeding.
High-visibility patrols will be stationed on roads across the country to ensure motorists are driving at safe speeds.