Met Eireann have this morning extended their weather warning to cover all of Connacht as well as Cavan, Monaghan and Donegal.
Weather chiefs originally issued the warning for just four counties but updated it this morning as the torrential rain hit.
The advice will be in place until 9pm this evening as the weather front makes its way in from the west and across the country.
The warning states: "Further falls of heavy rain today with localised flooding and hazardous driving conditions."
All areas of the country are expected to be hit by the heavy rain with flooding a possibility in many parts.
The forecaster added: "Dull this morning with spells of rain, giving heavy falls in places and a risk of localised flooding. It will become drier over much of Leinster and Munster this afternoon.
"Rain will continue in Connacht and Ulster and will spread southeastwards this evening. Highest temperatures of 17 to 22 degrees with moderate southerly winds.
"Early tonight, rain will continue to affect Munster, Leinster and east Ulster. It will gradually clear southeastwards with clear spells and scattered showers following from the northwest. Lowest temperatures of 12 to 15 degrees with moderate southwest winds."
