Met Eireann has issued an urgent thunderstorm warning for ten counties.
The alert was originally in place for Cavan, Monaghan, Longford, Louth, Meath, Westmeath and Offaly immediately until 10pm on Monday - Galway, Roscommon and Leitrim have since been added.
It reads: "Heavy showers or thunderstorms may lead to localised flooding and hazardous driving conditions."
Meanwhile, there will be brief respite from the awful conditions on Tuesday as a largely dry day is expected.
However, it will turn unsettled once again as the week goes on with further showers and a low pressure system moving across the north of the country.
A Met Eireann forecaster said: "Tomorrow, Tuesday, will be a largely dry day for many with just a few light showers about, mainly in the west. It will be a rather cloudy day overall, with the best of the sunny breaks occurring in morning hours or early afternoon. Highest temperatures of 17 to 20 degrees in light southwest or variable breezes.
"Tuesday night will be dry for many with clear spells. Some patchy rain and drizzle will affect western and southern coastal counties, however. Cloud will thicken overnight, with more persistent rain arriving in Atlantic coastal counties by dawn. A mild night, with lows of 13 to 15 degrees Celsius with light to moderate south to southeast breezes, freshening on coasts overnight."
A forecaster added: "Outbreaks of, occasionally heavy, rain will push eastwards over the country during Wednesday morning and early afternoon. Brighter, clearer and sunnier conditions with just isolated showers will develop in Atlantic counties by late morning, however, before gradually extending elsewhere through the rest of the day.
"Breezy at first with moderate to fresh and gusty south-easterly winds, but winds will veer to a lighter southwest as the rain clears through. Highs of 17 to 20 degrees Celsius. Largely dry with long clear spells for most on Wednesday night. Cloud and patchy drizzle will develop along Atlantic coasts overnight. Winds be mainly light to moderate southerly, but they'll increase fresh to strong and gusty along western and southwestern coasts by dawn. Lows of 9 to 13 degrees Celsius.
"Current indications suggest low pressure will track just north of Ireland on Thursday, making for a very blustery or windy day with sunny spells and heavy showers, especially in the west and northwest. Southwest winds will be strong to near gale force on Atlantic coasts with some high seas here. Inland, southwest winds will be mostly fresh to strong. Maximum temperatures will range 17 to 19 degrees Celsius.
"Still quite windy early on Friday, but with moderating westerly winds into the afternoon. Sunny spells and scattered showers are expected with driest, brightest and mildest conditions in the southeast. Highs 16 to 20 degrees Celsius."
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