Met Éireann has issued a new Status Yellow rainfall warning for 18 counties this morning, Wednesday, August 7.
The warning will be valid from tomorrow evening from 7:00pm through to Friday morning at 7:00am.
The warning will affect all counties in both Munster and Leinster.
Spot flooding is likely, Met Éireann warns.
Meanwhile, today will start mainly dry with sunny spells and just isolated showers, according to the national meteorological office.
The showers will become more widespread this afternoon and evening, with some heavy and thundery bursts, particularly over midlands, north and east.
Top temperatures of 17° to 21° are expected for the day in moderate westerly breezes.
Lowest temperatures will fall to around 8° to 11°. Winds will fall light with mist or fog patches forming.
Tomorrow will be a mainly dry day with just a few isolated showers and good sunny spells at first, but cloud will increase later with a spell of rain pushing into Munster and south Leinster by evening.
Top temperatures will be 18° to 22° in light east to southeasterly breezes but increasing moderate to fresh later.