Weather warnings are in effect across the country overnight, including a red wind warning for Co Cork.
Met Éireann said Storm Ellen will "produce a core of very severe and destructive winds" between 9pm and midnight on Wednesday in Cork.
Earlier the forecaster said it had concerns for tourists in the south and in the west, as the storm approaches Ireland.
Orange weather warnings are now in effect for Munster, Galway and Mayo until 6am on Thursday morning amid expected "severe and damaging winds".
Meanwhile, the rest of the country has been issued with a status yellow wind warning for Wednesday night and throughout Thursday.
Evelyn Cusack, head of forecasting with Met Éireann, told Newstalk Breakfast this could change.
"We have orange level warnings out for land and for marine areas as well.
"Storm Ellen is going to hit Kerry, the south-west of Ireland, later this evening.
"And then zip up along the west, or perhaps in over Ireland, tonight.
"So the worst of the winds will actually be during the night hours - but they're likely to be quite damaging winds.
"So we are obviously worried about the huge amount of tourists, especially in the south and in the west - very dangerous conditions indeed.
"But while the worst of the winds will pass tonight, tomorrow and Friday will be very windy days as well.
"There will be gales and very rough seas."
"So while the storm itself may pass tonight, you're in for a very, very poor unseasonable and very challenging few days."
"While we have yellow country-wide, a yellow wind warning is for very high winds as well.
"So take it that we could have orange impacts really anywhere across the country.
"Still the track has a little of uncertainty associated with it - so all areas really to be on alert for orange level impacts tonight.
"And really through daytime tomorrow and Friday as well, while maybe not very extreme, certainly very serious and unseasonable for the time of year."
"There's going to be some more flooding: both from coastal areas - really any coast including the east coast over the next couple of days - but also perhaps some rivers and in land areas."
She also warned there could be high waves on lakes, and advised that people should not be out hill-walking.
A wind warning is also in place for Northern Ireland - counties Antrim, Armagh, Down, Fermanagh, Tyrone and Derry - from the UK Met Office.
