A Status Orange weather warning has been put in place for 15 counties amid the threat of potential thunderstorms and lightning strikes.
Met Éireann said local intense rainfall of up to 50mm is expected in Carlow, Kildare, Kilkenny, Laois, Longford, Offaly, Westmeath, Cavan, Donegal, Leitrim, Roscommon, Sligo, Waterford.
Wexford and Wicklow have now been added to the list of counties affected.
The warning will be valid from 4am to 8am tomorrow morning.
People attending the Electric Picnic festival in Stradbally, Co Laois, have been warned to protect themselves from the elements, with many of the 70,000 in attendance camping overnight.
Level: Orange— Met Éireann (@MetEireann) September 3, 2022
Local intense rainfall (50mm), and squalls likely.
See yellow warnings also.👇https://t.co/l8JdKfwZt9
Expected Onset: Sunday 4/9/2022 04:00
Expires: Sunday 4/9/2022 08:00 pic.twitter.com/Oj4XckR8qw
There is also a Status Yellow rain warning for all of Ireland set to come into effect at 1am. It will last until 10am tomorrow.
Met Éireann said "heavy rain will move northwards across much of the country tonight, clearing from the north and northwest on Sunday morning".
"Some torrential downpours are expected in parts, resulting in surface flooding. There is also the potential for thunderstorm activity and lightning strikes."
'Thunderstorms through the night' at Electric Picnic
Festival-goers at Electric Picnic are being warned to prepare for heavy downpours overnight.
Joanna Donnelly from Met Éireann said thunderstorms are also expected throughout the night.
More than 70,000 people are expected at the festival in Stradbally, Co Laois over this weekend for the arts and music festival.
Speaking to RTÉ News, Ms Donnelly warned those staying at the venue tonight to make sure they are "well protected from the elements".
"It is overnight tonight that is going to see the period of the worst weather, with thunderstorms through the night, so if you are in a tent make sure you are well sealed up and well protected from the elements. It is going to be a rough night overnight."
The forecaster said there will be "deluges" of rain in some parts.
"We've got this ongoing period of heavy rain coming through.
"It has been raining all day today for many places, which is clearing away, but there is more coming back in the flow, some heavy, and some thunderstorms in there as well giving deluges of heavy rain coming through in those downpours."
She explained this amount of rain is not unusual at this time of year due to the heat and moisture in the atmosphere.
"It is pretty normal because there is still a lot of heat around and a lot of moisture in the air.
"We have had a very dry weather over the last few weeks. So coming in after that dry period the rain isn't soaking into the ground so easily, so we have a lot of pooling and puddling."