People are being told to plan for a "very wet day", with the risk of spot or localised flooding in some areas.
Met Éireann has issued status yellow rain warnings for ten counties - Carlow, Cork, Kerry, Kildare, Kilkenny, Laois, Wexford, Wicklow, Tipperary and Waterford.
The warnings - which are valid until early on Thursday morning - warn that heavy spells of persistent rain will lead to localised flooding.
Met Éireann says other parts of the country can also expect heavy rain throughout the day, with further wet weather expected for the rest of the week.
Alan O’Reilly from Carlow Weather spoke to Breakfast Briefing about the bad weather that lies ahead.
He said: “We’re certainly preparing for a spell of very heavy rain.
“It’s 16 degrees here this morning, so it’s warm rain as opposed to the colder wet weather… but certainly some very heavy rain coming, and it’s going to lead to some spot flooding.
“People are going to want to take care out there - especially on roads, there’s a risk of some localised flooding.
“There will be rainfall across all areas at times… but certainly the worst of it will be in the south-east and south.”
He said the weather warnings expire early tomorrow, but the wet conditions are likely to continue into tomorrow - with thunderstorms also possible.
Up to 40mm of rain is expected over the next 24 hours - with Alan noting that the conditions at this time of year, including falling leaves blocking chains, can lead to flooding.
He noted: “Generally yellow rainfall warnings are less than 50mm in 24 hours, but it really can depend on how quick the rain comes down.
"It’s more a ‘be aware’ than ‘be worried’... but if you are going to be out today, you are going to want to plan for a very wet day.”
Today's weather follows a mild September and October, where temperatures have stayed above the usual seasonal norm.
However, Alan says early indications are that temperatures may drop next week.
He also said it looks like there could be some wet weather ahead for those planning to head out for Halloween trick or treating on Sunday.