Cavan and Monaghan are among nine counties currently under a status yellow weather warning.
This is expected to stay in place until 6pm tomorrow.
Dublin, Wicklow and Waterford and Louth will remain under an orange warning until varying times tomorrow.
Forecasters are warning that further rain falling on already saturated ground combined with high river levels and high tides will lead to localised flooding, river flooding, and difficult travel conditions.
Speaking on the Joe Finnegan show this morning, Monaghan forecaster Gerry Murphy outlined what to expect in Cavan and Monaghan.
"This scenario of very heavy bands of rain pushing up from the south is continuing. The current band of rain, which is now affecting parts of Cavan and Monaghan, will continue for the rest of today, all the way through tonight and for a good part of tomorrow as well.
So it's a fairly prolonged wet spell for the rest of today, overnight, and a good part of tomorrow, Friday. For County Monaghan and especially East Cavan, we can expect between about 20 and 40 millimetres of rainfall, which is within the yellow threshold, and then possibly not quite so much further west in Cavan. Overall, because the ground is already saturated and because river levels are high, there is always the potential for some flooding from that, especially further to the east of these regions."
