The Met Office has issued a severe weather warning as heavy rainfall is expected to continue across Northern Ireland.
Roads in Omagh, Scraghey, Drumquin and Clady have been closed due to the severe levels of rainfall earlier on Sunday.
The Met Office Yellow Warning will remain in place for most of Sunday.
"A moist, west to southwesterly flow will dominate over the area during the period. Heavy rain could deliver 20-40 mm widely with 60 mm possible in the west," said the Met Office's short term forecast.
It added: "This rain is set to fall on already saturated ground. Please be aware that this will lead to difficult driving conditions and could cause localised flooding, particularly in the west."
There were also reports of flooding in the Irish Republic, as far south as Cork.
Stormy conditions knocked out power supply in the Carrickmines area of Dublin on Saturday night, with customers also cut off in counties Wexford, Donegal, Galway and Clare.
Met Eireann forecast persistent rain in the west throughout Sunday afternoon, spreading eastwards to all areas later.
The Police Service of Northern Ireland and the Garda urged road users across the island to exercise extra caution due to surface water.