Commuters across the country have been hit by disruptions today due to the severe weather conditions.
The major emergency plan for the Dublin Region has been invoked by Dublin City Council and South Dublin County Council.
A major rescue operation is underway in the Wicklow Mountains after a man was swept away near Ballysmuttan Bridge, close to the Sally Gap. Members of the Glen of Imaal and Dublin-Wicklow mountain rescue teams are at the scene
All Northern commuter, Belfast enterprise, Sligo and Maynooth commuter services and Darts have been suspended due to flooding. The Luas red line is only operating between Tallaght and Blackhorse at present. Luas Green Line services are only running between Brides Glen to Beechwood. Diversions are also in place on a number of Dublin Bus services while a number of flights were diverted to Shannon airport.
The Garda and AA Roadwatch have appealed to motorists to take extreme caution and to only drive if necessary.
The Met Office said that over one month's worth of rain has fallen in the past 24 hours at Casement Aerodrome.
Dublin Fire Brigade and the Coast Guard have been overwhelmed by the number of calls they have received from members of the public.
Excess surface water is a problem in many areas and visibility is also poor where heavy rain is falling. A number of ferry services to and from Dublin have been cancelled.
Flooding is causing serious problems for drivers in the capital. A number of roads are closed including the Ballybough road, the Dodder road and Rock road.
In the city centre, there is flooding in Inchicore, Kimmage, Ballyfermot, Kilmainham, Harold's Cross, Dolphin's Barn, Donnycarney, Harrington street, Harcourt road and South Richmond street. Carysfort avenue in Blackrock is described as almost impassable due to severe flooding while heavy rain is also reported in nearby Monkstown and in Tallaght.
The Lower road at Strawberry Beds is now closed to all traffic and Dundrum Shopping Centre was evacuated due to ground floor flooding.
There are serious delays reported on the M1, the M7 and the M50. The M50 is now closed northbound between Leopardstown and Firhouse. One lane of the MI motorway is closed between the Airport and Balbriggan.
Treacherous conditions are reported on the N81 Dublin to Baltinglass road in Co Wicklow and motorists are advised not to use the Sally Gap, Wicklow Gap and all access roads to Valleymount and Lacken.
Gardai are advising motorists in Blessington, Co Wicklow to stay off the roads unless absolutely necessary due to severe flooding the area.
Flooding is also reporting in counties Louth, Monaghan, Laois, Kildare, Meath, Waterford and Kerry.
Met Éireann said spells of heavy rain affecting Ulster, Leinster and parts of east Munster will clear early tonight. Elsewhere, patches of light rain will soon die out but it will stay cloudy for a time. Isolated showers are expected to develop overnight near western coasts, otherwise there will be clear spells, and fog will form widely inland.