In Galway city, coastal routes along the harbour are closed as a precaution ahead of high tide at around 7.45am.
The Met Office has warned that homes and offices are likely to be flooded, and fast flowing or deep floodwater could cause a danger to life.
Areas of high ground exposed to the south and south west will be most affected, with the potential for a further 40-60 mm downpour over hills.
Up to 5 inches (120-160 mm) of rain is possible over higher ground in the south and southwest of the United Kingdom, approaching the region's monthly average.
Parts of southern Scotland are set for more dismal weather throughout the rest of today and tomorrow, with persistent heavy rain forecast. "In addition, leaves and twigs, brought down by the wind, could block drains and culverts, increasing the likelihood of flooding". "That's quite a substantial amount of rain to come and could bring flooding".
There has also been reports of tress down and flooding in parts with warnings of hazardous conditions through the day.
Here, Clare County Council has held meetings involving various responders as they monitor the expected situation locally.
Rail services to Drogheda, Dundalk and Belfast have been suspended because of a tree on the line at Donabate in Dublin.
The National Emergency Coordination Group is to be meet at 3pm this afternoon to discuss preparations and response to the storm.
While heavy rain is expected to continue into Saturday, the wind is now forecast to ease off by Friday evening. Spray and flooding is also likely to lead to hard driving conditions and some road closures.
Already there are delays and cancellations to train and bus services.