Met Éireann has urged people to prepare for "treacherous" conditions tonight and tomorrow as temperatures drop below freezing, and to stay inside if they can.
A Status Yellow low temperature/ice warning is in effect nationwide since 9pm until 10am tomorrow, with the forecaster warning of hazardous travel conditions and travel disruption.
After that warning expires, a Status Yellow rain warning will come into operation for Cork and Kerry from 12pm until midnight, with heavy rain leading to possible spot flooding and difficult travelling conditions.
A separate Status Yellow warning for rain and snow has been issued for Cavan, Donegal, Connacht and Longford.
The forecaster said rain, which will be heavy at times, will turn to sleet or snow in some areas, which along with strengthening winds will lead to poor visibility and difficult travel conditions.
The warning will be in effect from midday tomorrow until midnight.
Temperatures could fall to -4C in some areas overnight, with a sharp frost and icy conditions forecast.
Speaking on RTÉ's Drivetime, Met Éireann meteorologist Linda Hughes advised anyone travelling tomorrow to do so as early as possible, with the best of the weather to come in the morning.
"There's a mix of hazards out there tomorrow, so give plenty of time as always. Slow down on the roads as there will be some treacherous conditions with the ice followed by that heavy rain and possibly sleet and snow in the northwest as well," she said.
"So if you can, stay inside for tomorrow," she added.
It comes after several areas of north Dublin experienced significant levels of flooding after heavy rain fell overnight.
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High water levels in the Liffey and Grand Canal in Dublin are being monitored after heavy rain led to flooding in the city.
Dublin City Council said it is "actively monitoring elevated surface water levels across the city", particularly in the Liffey at Chapelizod, and is working with Waterways Ireland on "heightened water levels" in the Grand Canal.
The council said a full review is under way into the flooding, which will look at the "timeliness" of weather warnings.
It also said its crews will "remain active across the weekend" to implement mitigation measures and tackle any "further issues" that may arise.
Watch: Cars submerged in underground car park in north Dublin
Areas in Fingal County Council were among the worst impacted, while Clongriffin in the Dublin City Council area was also severely affected.
Questioned this afternoon about the late issuing of a Status Yellow rainfall warning at 2.37am, and whether it could have been given earlier, Met Éireann meteorologist Mark Bowe said it was "a complex and evolving" situation.
Sources in local government said the warning came too late and that previous warnings were insufficient to prepare for the amount of rain that fell overnight.
Both local authorities deployed crews overnight to respond to the heavy rainfall and they are working to pump water away from roads and areas that have been impacted by flooding.
Dublin City Council said 46mm of rainfall was recorded at the Mellowes Road rain gauge, with 9.6mm falling within a single hour.
"Combined with already saturated ground conditions, this resulted in significant surface water runoff and a number of flooding incidents across the city," it said.
"Significant impacts were reported in several areas, including Clongriffin and Ballymun, where localised flooding affected roads and properties.
"In Clongriffin, an Uisce Eireann foul sewer surcharged, resulting in road damage and property flooding."
"We recognise the distress flooding can cause for residents and businesses and will continue to provide updates as further verified information becomes available."
Dublin Airport said flight operations were running as normal, but some roads leading to the area were closed or "trickier than usual to navigate".
It said: "Drivers are advised to follow local diversion signage and to take extra care on the roads."
Dublin Bus advised customers that four routes serving the airport had been diverted because of flooding at Collinstown.
Bus Éireann said adverse weather conditions and flooding have affected some roads on its scheduled services.
Several of its services in the east of the country had been cancelled or delayed.
