Met Eireann has issued a fresh rainfall warning for three counties as up to 35mm of rain is expected to fall.
Forecasters issued the alert for Donegal, Mayo and Galway on Thursday morning and it will remain in place until 3pm on Friday afternoon.
A forecaster said: "Spells of persistent rain will give totals of 25 to 35 mm in parts, mainly over high ground."
However, it will be much nicer tomorrow in the south and east where temperatures could reach highs of 22C.
A forecaster said: "The south and east will be drier and brighter again. Later in the day the rain will move eastwards and it will become mainly dry in the west.
"Highest temperatures of 15C to 22C, warmest in the south and east. Southwest winds will be moderate to fresh."
Looking ahead to Saturday, revellers heading to Forbidden Fruit and Bloom in the Park will enjoy mainly dry conditions with the odd bright spell.
A forecaster said: "Top temperatures will range between 14C and 18C. A more persistent spell of rain will move in from the Atlantic during Saturday night, heavy for time, especially about higher in the west.
"Lowest temperatures will be around 11C to 13C in light southerly breezes which will increase moderate later."
Meanwhile, Sunday morning will start off rainy with sunshine and showers during the morning and early afternoon.
Some heavy bursts are likely in Ulster and northwest Connacht.
It will be less humid with top temperatures of around 14C to 18C but it will feel cooler in the fresh and gusty westerly wind, strong along Atlantic coasts.
