Met Éireann say that strong southeast winds associated with the storm coinciding with high spring tides will affect Ireland on Thursday night and into Friday morning.
NRW has also advised people to take extra care will driving, to avoid walking or driving through any flood water, and to avoid fast flowing rivers and streams.
Image - Met Office impact matrix for Friday's wind warning.as event become more likely, could rise to an Amber warning.More news: US, Russia space crew aborts mission after booster failure
Not yet formed, but later Thursday into early Friday, a rapidly deepening Atlantic storm depression (936hPa), will advance towards the west of Ireland and track northwards, eventually pulling away towards Iceland daytime Friday.
On Saturday, heavy rain is expected across most of the country as it looks set to be a wet weekend.
Rain will clear to showers in Northern parts but further heavy rain is likely to spread into Southern and Eastern areas with the ongoing flooding risk.
The RSA said that with the risk of coastal flooding, motorists should not attempt to drive through flooded areas.More news: Dow Falls 430 Points as Bond Yields Surge and China Tensions Grow
A Met Office spokesman said: "As Storm Callum passes to the northwest of the United Kingdom, a period of heavy rain will affect South Wales during Friday, with further spells of persistent and heavy rain at times during Saturday".
"Despite clearance efforts by the Council, the high winds will increase the amount of falling leaves and block drains very quickly, exacerbating flooding" he warned.
Head of Forecasting at Met Eireann Evelyn Cusack said a combination of storm-force winds and high tides means there is a possibility of flooding along the east, south and west coast as far north as Donegal.
The extreme conditions triggered two yellow - "be aware" - warnings from the Met Office after a similar alert on Tuesday caused flooding and travel disruption to roads, railways and ferries.More news: Bipartisan Senate Group Forces U.S. Probe of Saudi Journalist's Disappearance
The storm is expected to bring heavy rain between 6am on Friday and 6pm on Saturday, particularly over south-facing hills.
- Strictly Come Dancing contestant Seann Walsh under fire from ex-girlfriend
- Dow sinks 800 as tech companies decline
- Nokia 7.1 Plus Expected to Launch Today in India
- Der Spiegel stands by Cristiano Ronaldo rape allegation reporting
- Samsung launches A9, world's first smartphone with four rear cameras
- Sarah Silverman Rips 'Too Far Gone' White Women Who Voted for Trump
- Google is extending Home Control from this week
- Selena Gomez Wrote About 'Negative Comments' in Last Instagram Post Before Hospitalization
- British couple killed as their taxi is swept away in Mallorca floods
- Saudi envoy to US expresses shock at false reports