A Met Éireann rain and thunderstorm warning for counties Clare, Kerry, Limerick and Galway has come into effect.
With the sweltering weather of recent days being replaced by more unsettled conditions, the forecaster said heavy downpours and possible thunderstorms were to be expected in the four western counties until 7am on Tuesday.
The potential impacts include surface water flooding, lightning damage and difficult travelling conditions, it added.
An earlier thunderstorm warning for counties Carlow, Dublin, Kildare, Kilkenny, Laois, Louth, Meath, Offaly, Westmeath and Wicklow expired at 4pm.
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The hot weather at the weekend broke on Sunday evening with very heavy rain, thunder and lightning in counties Mayo and Galway.
Otherwise, a cool and unsettled week is in store, in contrast to last week’s weather that featured the hottest temperatures for three years.
A temperature of 31.1 degrees was recorded at Mount Dillon, Co Roscommon, on Saturday as the country sweltered in a short but intense heatwave. It was the highest temperature recorded in Ireland since July 2022.
Temperatures will be nowhere near that mark this week. It will feel notably fresher too, with winds from the northwest keeping temperatures closer to normal.
Monday will be a showery day with highs of 21 degrees, and it will be the same on Tuesday.

According to Met Éireann, Monday will be generally dry early on across Ulster and Leinster. Later this afternoon, cloud will increase across the west and southwest of the country, with longer spells of rains and some thunderstorms expected in those areas.
It will feel slightly warmer on Wednesday and Thursday with a couple of muggy nights in store. A lot of places will see night-time temperatures of 17 degrees on Thursday.
The weather into next week is for more of the same, with low pressure dominating. The low pressure is expected to bring showers or longer spells of rain at times. Temperatures will be around average for July.
The UK Met Office has said the recent heatwaves in Britain are part of an upward trajectory in temperatures across northern Europe.
Met Office climate scientist Mike Kendon said the weather is now “notably different” to what it was a few decades ago. “We are now seeing records being broken very frequently as we see temperature and rainfall extremes being the most affected by our changing climate”.