Met Éireann has issued a Status Orange rainfall warning for 13 counties, with the early part of the morning set to see heavy rain in these areas.
The national forecaster had issued a Status Yellow warning for the whole country, which was due to come into effect at 9:00p.m tonight (Saturday, September 3).
However, Met Éireann has updated its warnings, with both a Status Orange rainfall warning and a Status Yellow rainfall warning (at times and locations not covered by the former) now being issued.
The Status Orange warning will apply to counties Carlow, Kildare, Kilkenny, Laois, Longford, Offaly, Westmeath, Cavan, Donegal, Leitrim, Roscommon, Sligo, and Waterford.
Local rainfall will be intense (up to 50mm in some areas), and squalls are likely.
This warning will be valid from 4:00a.m to 8:00a.m tomorrow (Sunday, September 4).
When this warning expires, these counties, along with the rest of the country, will be subject to a Status Yellow warning.
Heavy rain will move northwards over most of the country tonight, clearing from the north and northwest tomorrow morning.
Some torrential downpours are expected in parts, resulting in surface flooding. There is also the potential for thunderstorm activity and lightning strikes.
The Status Yellow warning will come into effect at 1:00a.m, and will remain in place until 10:00a.m tomorrow morning.
The Met Office in the UK has also issued a further warning for all counties in Northern Ireland.
The equivalent of a Status Yellow warning had already been issued yesterday to cover all of today for counties Antrim, Armagh, Down, Fermanagh, Tyrone, and Derry.
Now a further waring has been issued for Northern Ireland which will come into effect at 2:00a.m and remain in place until 11:00a.m tomorrow morning.
Heavy rain may cause travel disruption and flooding in a few places, according to the UK Met Office.