Potentially torrential rain is on the way as Met Éireann issues a weather warning for across the country.
Rainfall of between 25mm and 30mms in a short time is expected in many parts of the country.
The rain will sweep into western areas by mid-afternoon and reach the east coast by this evening.
Rainfall will come in bursts of thundery showers and they will be localised, with possible spot flooding in places. All areas are at risk of heavy showers.
The rain heralds the end of a glorious spell of weather lasting 10 days in a heatwave that saw temperatures over 30 degrees in several locations.
A yellow weather warning is in place for the State from midday on Monday to 5am on Tuesday morning.
Tuesday will see further heavy downpours though not as intense as Monday, but further heavy rain is expected on Wednesday.
Met Éireann forecaster Emer Flood said the change in the weather this week will "come as a shock to the system" as a normal Irish summer returns with cool, changeable conditions.
“The heatwave is well and truly gone. My advice is that if you are driving in a heavy showers, slow down. Be mindful of spot flooding.”
Although the rain will be heavy, it will be nothing like the floods that have affected London and the southeast of England. "We don't have the heat today that would bring that level of energy to it," she said. "It's a different set-up to what Britain is seeing."
The longer term forecast is for more of the same with heavy showers and the risk of lightning on Thursday and Friday.
Early indications suggest next weekend will be fresh and bright with a mix of sunshine and scattered showers with temperatures close to average
