Storm Ciarán will track eastwards off the southern coast later as rain and wind grip parts of Munster and Leinster.
A Status Yellow rain warning is in place for 24 hours from 7pm tonight for Carlow, Kilkenny, Wexford, Wicklow, Cork and Waterford.
A separate Status Yellow rain warning is also in place for Kerry until midday today, along with a wind warning for Clare, Kerry and Galway until 11am.
Met Éireann Meteorologist Mark Bowe told Newstalk Breakfast the rain will get heavier as the day goes on.
"It's a very dull, damp and wet day ahead," he said.
"We do have scattered blustery showers moving over the country at the moment and some of those showers will be heavy at times and squally too.
"We are expecting the arrival of Storm Ciarán later on this evening. It is going to track eastwards off the southern coasts of the country.
"So, later on this evening, cloud is going to build along southern counties - counties across Munster and south Leinster - and we will start to see outbreaks of rain.
"The rain will become heavy later on tonight as Storm Ciarán tracks even closer.
"All this rain, combined with already saturated grounds and high river levels in these counties may lead to some flooding.
"So, it's going to be a very wet day indeed, especially across those southern counties.
"By tomorrow morning, Storm Ciarán will move off towards the UK, but it will leave behind scattered blustery showers for the morning."
'Raining constantly since July'
Minister of State at the Office of Public Works, Patrick O’Donovan, told the show it isn't good news for landowners.
"The reality is it has been raining pretty much constantly now since July with a short break there in the early part of October," he said.
"If you talk to any landowner, anybody involved in agriculture, they'll tell you that literally the best of free-draining soils in the country are totally saturated at the moment.
"Dykes, streams and rivers have never been higher for this time of the year.
"We're getting unprecedented levels of storm activity so early and we haven't even gone into the winter.
"So, it isn't good news unfortunately for a lot of counties where rivers could potentially be at bank level and where the water will literally have nowhere else to go other than out over the bank.
"A lot of these counties are stretched already; they've had multiple events already."
Flood relief schemes
Minister O’Donovan said a number of towns have been protected over the last number of years.
"Now almost 25,000 individual properties have been protected by built flood relief schemes.
"Towns like Clonmel, Fermoy, Mallow, Bandon, Skibbereen, Ennis.
"In the later part of this year we'll be completing ones in Ashbourne and Clonlara in Co Clare, with Templemore in Co Tipperary almost completed.
"We're working with the local authorities to build out a further 100 of these schemes across the country in towns and villages, and indeed cities as well like Galway, that will prevent the worst excesses of what we've seen.
"It is a slow and arduous process and we have to take each step as it comes," he added.