It's not looking good.

The counties affected are Cavan, Donegal, Monaghan, Clare, Cork, Kerry, Limerick, Tipperary, Longford, Louth, Meath, Offaly, Westmeath as well as the whole of Connacht.

The national forecaster predict that a band of heavy rain will move eastwards Sunday night and early Monday, with thundery downpours possible.

Potential impacts include localised flooding, difficult travelling conditions and poor visibility.

The warning is valid from 10pm on Sunday, August 11, until Monday at 7am.

The UK Met Office have also issued a Thunderstorm Warning for Antrim, Armagh, Down, Fermanagh, Tyrone, Derry - valid from midnight until 7am on Monday, August 12.

Update:
Status Yellow - Rain warning for Cavan Donegal Monaghan Clare Cork Kerry Limerick Tipperary Connacht Longford Louth Meath Offaly Westmeath

A band of heavy rain will move eastwards Sunday night & early Monday, with thundery downpours possible⤵️https://t.co/lvQFgW8DsS pic.twitter.com/hdAWI47tOt

— Met Éireann (@MetEireann) August 11, 2024

Rain warning issued for 18 Irish counties as thundery downpours possible

As for the rest of Sunday, Met Éireann predict that cloudier conditions with patchy drizzle, mist and fog affecting mainly the south and west will replace the brighter conditions from this morning.

Cloud will gradually increase through the afternoon, and scattered showers will develop, with some turning heavy in the west and southwest this evening. Highest temperatures 20 to 25 degrees with east to southeasterly winds increasing moderate to fresh.

For Sunday night, rain is expected, heavy at times, with the chance of thunderstorms and localised flooding, moving northeastwards over the country tonight.

Lowest temperatures 13 to 16 degrees with moderate, occasionally fresh, southerly winds veering westerly with the clearance of the rain.

Tomorrow, Monday, is expected to be mostly dry with sunny spells and some isolated showers near western coasts.

Highest temperatures 18 to 22 degrees with light to moderate southwesterly winds.

From Monday night, rain and drizzle will become widespread, with lowest temperatures 13 or 14 degrees in moderate to fresh and gusty southerly winds.