Well discussed on other threads so worthy of a thread of its own I think.
Some heavy rain is forceast to move in over many parts of Ireland tomorrow evening as a frontal zone, currently developing to the west of Ireland, gets caught up in a strengthen jet and makes its merry towards Ireland.
ECMWF forecast chart for noon monday:
Heavy pulses of rain are forecast to pump up over Ireland through sunday night into a good part of monday, with the eastern half of the country most at risk of the heaviest bursts with more showery conditions (which could be still heavy) forecast to develop further west during monday afternoon.
My advice is to enjoy it!