Met Éireann has issued a moderate Yellow rain warning for Donegal and all other counties.
The alert is already in effect and is valid until 11pm on Thursday night.
The national meteorological service says that, on Tuesday and Wednesday, there will be heavy showers or longer spells of rain at times with flooding likely in places, as soils are saturated and river levels are high.
Squally showers tomorrow morning will be accompanied by very gusty conditions. Later on Wednesday, and on Thursday, further rainfall associated with Storm Ciarán may lead to flooding. It is likely, however, that the heaviest rain will be in southern and eastern coastal counties.
Additional impacts include poor visibility and difficult/dangerous driving conditions.
