Torrential downpours caused localised flooding Cork, Tipperary, Laois, Kildare, Wexford, Wicklow, Carlow, Meath and Dublin, making driving conditions extremely hazardous.
Cork city and county were particularly badly affected. The AA said they were called out to help drivers stuck in floods, most notably around Kinsale.
Nicola Hudson, of AA Roadwatch, said it was a dangerous day on Irish roads – which have claimed 180 lives so far this year.
The M8 was affected southbound at the junction 17 turnoff to Watergrasshill. There was flooding also on the N25 Carrigtwohill-Midleton road at Lynwen Lodge and Minister Hill.
In Cobh there was flooding in the Lower Road and Ticknock area, and in the city the areas affected included Sundays Well Road, North Ring and Mayfield.
Parts of Carrigaline and Douglas were also hit, with shopkeepers desperately stacking sandbags and trying to remove leaves which were blocking drains.
In the city centre there was also localised flooding, particularly at Monaghan Road, Anglesea Street and South Terrace.
Ms Hudson said there had been a big increase in the number of breakdown call outs to the AA Rescue Service.
“We had a number of cars overheating while stuck in traffic in heavy rain, notably at the scene of the roadworks on the N7 at Rathcoole. Wet weather can cause problems with a car’s electrics, so a lot of drivers will find their cars struggling to start over the weekend,” she said.
“The downpours also caused problems in the Portlaoise area and on the M7 and M8 motorways.”
Ms Hudson warned drivers not to tailgate and to be especially careful on motorways – where a car travelling at 120km/h can take more than 170m to stop.
Motorists were also advised to look out for cyclists and motorcyclists.
“It is all too easy not to see a bike when the car glass is wet and misted. Check your blind spot with extra care when changing lanes,” she added.
Met Éireann said today would remain mostly dry apart from some isolated showers, with rain pushing into the southwest later in the evening. Rain will be a feature in most parts on the country tomorrow morning, but it will start clearing from the south in the evening.
Further rain is forecast for Monday.