Met Éireann says a storm due to hit tomorrow could be as bad as the infamous 'Hurricane Charlie' of 1986.
110km an hour winds and torrential rain are forecast, with the south of the country most at risk.
There are fears that a combination of the weather and high tides could cause many rivers to burst their banks.
Forecaster Vincent O'Shea says an unseasonal low pressure is to blame: "I hate to say it but it may be reminiscient of the infamous 'Hurricane Charlie' way back in 1986.
"It may not be quite as bad as that but we are expecting serious winds and extremely heavy rainfall across Munster and Leinster in particular.
"We are expecting a mount up of 50mm in parts of south Munster and south Leinster and remember those areas are already sodden."