A Status Orange rain warningissued for Waterford, Wexford and Wicklow will last until 8am today.
Met Éireann said there "will be additional significant accumulations of rainfallwith flooding in places".
The warning came into effect at 5.30pm yesterday and will last until 8am.
It follows heavy rain across ten counties across the south and east throughout yesterday.
Yellow rain warnings remain in effect in Cork, Kerry, Tipperary, Kildare, Laois, Carlow and Kilkenny until early today.
Status Orange - Rain warning for Waterford, Wexford, Wicklow— Met Éireann (@MetEireann) October 27, 2021
Following recent heavy rain today, there will be additional significant accumulations of rainfall this evening (Wednesday) and overnight with flooding in places.https://t.co/Xg3aMJlyuS
Met Éireann said heavy persistent rain will lead to flooding in some areas this morning.
The heavy rain in the southeast and east will clear during today, but more rain is expected to push up from the southwest during the day, bringing a risk of isolated thunderstorms.
Motorists urged to drive with caution
The Road Safety Authority is asking road users to exercise caution.
The authority is advising drivers that they need to slow down and leave a bigger space between themselves and the vehicle in front in wet weather conditions, especially on high speed roads, such as dual carriageways and motorways, where there is increased danger of aquaplaning
It advises that If a road ahead is flooded, the drivers should choose another route and not attempt to drive through it, as flooded roads that appear shallow could be deeper.
Road users are also encouraged to follow recommended routes, obey signs closing roads to traffic and, after going through water, drive slowly with a foot on the brake pedal for a short distance to dry the brakes.
Pedestrians, cyclists and motorcylists are advised to wear bright clothing with reflective armbands or a reflective belt to ensure they are seen in poor weather conditions.
When there are no footpaths, walk on the right-hand side of the road to face traffic.
Month's worth of rain forecast for parts of UK
The UK Met Office has warned of life-threatening flooding as it issued amber weather warnings for rain in north-west England and south-west Scotland.
Up to 300mm is expected to fall in parts of Cumbria and not likely to ease until tonight.
"In a 24-hour period you could see a month's worth of rain," Met Office meteorologist Annie Shuttleworth said, describing the weather as "notable".
"The rainfall total is much higher than the average rainfall for this time of year, definitely, and in general, for any time of year it's a lot of rainfall in a short period of time," she said.
Persistent and heavy #rain continues across southwest Scotland and northwest England with weather warnings in force ?? #Flooding and travel disruption is expected, so take care if you need to travel ??— Met Office (@metoffice) October 27, 2021
Check out the latest rainfall accumulations league table below ?? pic.twitter.com/cFr6wOpoA9
Two months' worth of rain could fall in some local spots, Ms Shuttleworth said, adding that the region sees an average of 160mm in a typical October.
Dumfries and Galloway in south-west Scotland are forecast to be hit by downpours from tonight until 9am today.
The Met Office said there could be a "danger to life from fast-flowing or deep floodwater".