Update 2.15pm: Met Éireann has updated its status yellow warning for rain to include Co. Limierick.
The warning will now affect 20 counties. The areas included are: Connacht, Cavan, Monaghan, Donegal, Dublin, Kildare, Laois, Longford, Louth, Wicklow, Offaly, Westmeath, Meath, Clare, Limerick and Tipperary.
Update 9.30am: A status yellow rainfall warning has been extended to four more counties.
The warning is now in place for Dublin, Kildare, Laois and Wicklow as well as the 15 counties previously named.
It will be in effect from 8pm tonight until 8am Monday morning.
Rainfall of 25mm or more is expected in areas.
The rain is likely to be preceded by a period of sleet and snow in parts of Connacht, Ulster and north Leinster, before turning to rain later in the night.
As the ground is saturated at the moment and river levels are elevated the combined effect of rainfall and snow melt may lead to some localised surface and river flooding.
Status Yellow - Rainfall Warning Update.
Update 7.13am: Homes and businesses in counties along the River Shannon are bracing themselves for possible flooding today.
Farmland along the river, including around Athlone and Carrick-on-Shannon, is already underwater but flood defences are working so far.
A status yellow rainfall warning for Connacht, Cavan, Monaghan, Donegal, Longford, Louth, Offaly, Westmeath, Meath, Clare and Tipperary will take effect from 8pm tonight.
"Locals are very concerned at the moment with the bad forecast we have," said Tom Cleary, a racehorse trainer near Athlone, which was badly affected by flooding in 2016.
"At the moment it's at a danger level and it will only take a couple more inches. There are some houses that will be badly affected with another couple of inches of water so they are very concerned."
Meanwhile, Mayo County Council spokesperson Noel Gibbons is warning motorists not to drive through flooded areas:
"We're pleading with motorists not to drive through flooded roads, particularly roads that have been closed, to check with their local media before they head to the road, local social media sites, the local authorities or AA Roadwatch just to check if there's any roads closed and if so to look at an alternative route."