People have been advised to work from home by the National Emergency Co-ordination Group in areas experiencing heavy rain and the threat of flooding.
A Status Orange rain warning remains in effect for Dublin, Wicklow, Waterford and Louth, while a Yellow warning is also in place for nine other counties as very heavy rain is expected over much of the southeast, east and north of the country.
Met Éireann is warning of rain falling on already saturated ground, which could cause localised flooding, river flooding and difficult travel conditions.
The Status Orange warning for Waterford is in effect until 9am.
The Status Orange warnings for Dublin and Wicklow will be in place until 3pm, while the warning for Louth will remain in effect until 6pm.
Watch: Wave overtopping in coastal areas of Co Dublin
Read more: Updates as they happen
Iarnród Éireann said that DART services are operating between Greystones and Howth, but there are delays through Seapoint due to impact of earlier flooding.
DART and Northern Commuter are suspended between Malahide and Howth Junction due to a mechanical issue.
It added that the Dublin to Rosslare train line is closed between Greystones and Kilcoole due to debris on the line and is also closed between Enniscorthy and Wexford due to flooding.
Flooding has been seen in Sandycove and other coastal areas of Dublin, with wave overtopping in places.
Motorists in affected areas are being warned not to drive into flood water.
The rail line near Dún Laoghaire which was damaged by high seas
Yellow rain warnings are in place
Separately, a Status Yellow rain warning is in effect for Carlow, Kildare, Kilkenny, Laois, Wexford and Tipperary until 9am.
Cavan, Monaghan and Meath are also under a Status Yellow rain warning until 6pm.
The UK Met Office said a Yellow warning for rain for is in effect for Antrim, Armagh, Down, Tyrone and Derry until midnight.
‘Better to work from home than risk your life’
The National Emergency Co-ordination Group (NECG) is warning of possible flooding and urged those in the affected areas who can work from home to do so “in order to free up roads for essential services”.
The group said local authorities are “monitoring the situation closely and actively responding to the weather conditions and associated flood risks”.
It said the Irish Red Cross and Civil Defence are also available to provide support where necessary.