Met Office chief meteorologist, Steve Willington, said: "Storm Dennis will bring another very unsettled spell of weather this weekend with a risk of flooding, particularly in parts of England and Wales".
Following hot on the heels of Storm Ciara last weekend, Dennis is set to cause damage as it tracks across the country today and tomorrow.
A yellow rain and wind warning is in place for the entire country until tonight.
On the strong winds heading to the region, the weather service said some short-term loss of power and other services is possible.
Met Éireann forecasts that average wind speeds will reach between 55 and 75 km/h, with gusts of up to 120 km/h expected.
There are also Status Yellow wind and rain warnings for the whole country over the weekend, with the unsettled weather expected to continue until Monday morning.
People watch waves and rough seas pound against the harbour wall at Porthcawl Wales
It came into effect at 9am today and will last until 8pm on Saturday, February 15.
Storm Dennis has caused widespread disruption to air and rail travel, with a number of high profile sporting fixtures cancelled.
"We recommend customers travelling to and from United Kingdom today, February 15th, to check the status of their flight and gate information on easyJet's Flight Tracker at www.easyjet.com/en/flight-tracker or on the app for latest travel updates".
"There are numerous locations of spot flooding on the road network throughout Co Laois".
"There will be very heavy downpours in the afternoon and evening, and there could be some localised flooding from Saturday afternoon into the evening", Mr Martin said.
During Sunday, the rain - which is likely to be squally and heavy as it moves through, will eventually clear the southeast corner.
Tomorrow is expected to be wet and windy with stormy conditions in Atlantic coastal counties, especially in northwestern counties. They'll also be falling as sleet and snow in the north and over high ground.