A warning is in place for strong winds and high seas tonight and tomorrow, with a risk of flooding in coastal areas.
Seven coastal counties in the west and south are under an orange warning for wind, with yellow-level warnings in place for the rest of the island.
The orange wind alert is in place for Galway, Mayo, Clare, Cork, Kerry, Limerick and Waterford until 1pm tomorrow.
Met Éireann says Storm Ellen is bringing with it a storm surge, heavy swells and onshore winds.
Forecaster Andrew Doran-Sherlock says Atlantic coastal counties will be worst affected.
"The indications are that it's coming in a little bit closer than it looked previously, there's a tighter gradient near the core so we're getting much stronger winds up along the south-west and western coast which is why we've upgraded the warnings for the Atlantic coastal counties."
