The west and northwest will be lashed by "persistent" rain today as Met Eireann issued a Status Yellow rainfall warning.
Met Eireann issued the warning for Donegal, Galway, Leitrim, Mayo and Sligo at 2pm yesterday and it will remain in place until midnight on Thursday.
The west and north west are at risk of flooding, with coastal areas and hills to be the worst affected areas.
A forecast said: "For the rest of Wednesday and all of Thursday, persistent and occasionally heavy rain at times with a risk of localised flooding.
Meanwhile, Bloom-goers will enjoy some “good dry spells” as they flock to Dublin today for the first day of Ireland’s largest gardening festival.
Daytrippers will enjoy highs of 19C to 21C in the capital, however it will be a mostly cloudy day, with some patches of light rain or drizzle.
A Met Eireann forecaster said: “Thursday will bring further spells of rain to Ulster, Connacht and North Leinster.
“Elsewhere somewhat drier with just some patchy light rain or drizzle, and some brighter spells may occur here with a few limited warm sunny breaks.”
Looking ahead to Friday, the outlook remains positive for Bloom with the south and east enjoying the warmest weather with balmy highs of 18C to 20C.
However, overall it will be cloudy with further outbreaks of rain, persistent in the west and north and somewhat drier in the southeast.
Top temperatures will reach between 14C to 20C, warmest in the south and east. South to southwest winds will be moderate to fresh and veer southwest to west and ease by evening.
And Saturday looks no better for the northwest, with further rain showers set to lash the area.
A forecaster said: "Saturday is likely to start mostly dry but further outbreaks of rain will push in from the south in a light southerly airflow.
"Top temperatures will reach between 14C and 17C. There will be further outbreaks of rain during Saturday night, possibly turning persistent and heavy in the west and north.
"Lowest temperatures will be around 10C to 12C in light southerly breezes which increase moderate later."
Meanwhile, Sunday will turn slightly cooler with highs of 13C to 16C and further showers predicted and strong winds along Atlantic coasts.
