Met Eireann has issued a fresh Status Yellow rainfall warning for four northwestern counties as up to 35mm of rain is set to fall.
The alert covers counties Sligo, Donegal, Mayo and Leitrim and comes into effect at 3am on Friday and lasts for 24 hours until 3am on Saturday.
Forecasters revealed there may be some "localised flooding" due to saturated ground and elevated rivers.
Met Eireann said: "25 to 35mm of rain expected during the period.
"As the ground is saturated at the moment and river levels are elevated the forecast rainfall may lead to some localised surface and river flooding."
And parts of Ireland will be hit by wintry showers on Thursday while there's also a risk of hail and thunder.
Met Eireann has warned that sleet showers are expected for areas in the north and west, with snow falling on high ground.
It will be nippy on Thursday afternoon with highs of just 8C, and windy too, as gales are forecast for western and northern coasts.
A forecaster said: "The last of the overnight rain will clear into the Irish Sea this morning.
"A blustery day ahead, with sunny spells and scattered heavy showers.
"The showers will be wintry at times, especially across the north and west with snow over high ground.
"There will also be a risk of hail and thunder. Showers becoming confined to the north and west by evening."
