From 12pm today until the same time tomorrow, a Status Yellow rain warning has been issued for Clare, Kerry, Galway and Mayo.
The national forecaster said heavy rain in these counties could lead to localised flooding and hazardous driving conditions.
While today is set to be a washout, brighter and sunnier weather is on the cards from Thursday onwards with cooler temperatures.
"A fairly wet start to the week, hopefully improving towards the end of next week for most areas,” Met Éireann forecaster Emer Flood said.
"Today is going to be quite wet across the country with some heavy falls of rain, particularly for Atlantic coastal counties. The heavy rain could lead to spot flooding.
"So fairly wet conditions, if you are out driving coming back from the Bank Holiday weekend somewhere there may be poor driving conditions out there, visibility could be quite poor, particularly in the afternoon and the evening.”
Damp and dreary conditions will continue into tomorrow with further outbreaks of heavy rain likely, but there should be some improvement in the evening with sunnier spells and some showers.
“Conditions slowly improving as the week goes on, so at the moment we are at a humid air mass, so even though it’s not particularly sunny for the next day or two the humidity is high so it feels quite muggy,” Ms Flood said.
"Tuesday could get up to 24 degrees in some eastern areas and it will be the warmest day of the week but not brilliant weather.”
From Wednesday the forecaster said it will feel a lot cooler, and although conditions will be drier temperatures will be cooler.
"They are actually going to be below average for this time of the year, mid to high teens, and western and northern areas will feel pretty cool at times, 15 or 16 degrees there.”
From Thursday high pressure is building so a lot of dry weather will be on the cards, especially for Leinster, Munster and the Midlands.
However, people living in northern or western coastal counties will see some rain or showers later on in the week, but it shouldn’t be too heavy.
For the weekend, Ms Flood said there will be “lots of dry weather on the cards but we can’t rule out some showers.
"Temperatures look like they could be improving over the weekend hitting the 20 degree mark in some places.”