The weather this week will be a 'complete change' to what it was during the heatwave, according to Met Éireann.
A Status Yellow rain and thunderstorm warning has been issued for the whole country.
The warning came into effect at 12pm and is expected to remain in force until 5am tomorrow.
Met Éireann said thunderstorms and heavy showers developing over the western half of the country will move eastwards this evening where they will continue tonight.
The forecaster is warning of downpours which will lead to 'dangerous driving conditions', with Leinster and east Munster expected to be impacted the most.
⚠️Yellow rain & thunder warning issued ⚠️
After a long spell of dry weather, rain returns today with heavy showers & thunderstorms possibly leading to surface flooding in a few areas.
See all active warnings here ➡️https://t.co/Xg3aMJlyuS pic.twitter.com/BENN1uYOtf
— Met Éireann (@MetEireann) July 26, 2021
While the warning is in place for just under 24 hours, forecasters say heavy showers will continue through Tuesday and Wednesday.
Meteorologist Emer Flood says it will remain unsettled for the rest of the week.
She said: "We're going into a much fresher air mass compared to last week.
"People can expect it feeling a lot fresher and much cooler, with best temperatures in the high teens to 20 degrees at best... with the threat of heavy, thunder showers."
She said there's likely to be widespread, heavy rain showers on Wednesday as well.
Current forecasts also suggest another "fresh and showery day" on Thursday.
Last week's heatwave saw temperatures top 30 degrees in some parts of the country, with 'uncomfortable' temperatures also continuing through the night.
However, cooler temperatures of 10-14 degrees are expected tonight and throughout the week.