The rainfall warning was issued for counties of Antrim, Armagh, Down, Derry, Tyrone and Fermanagh.
The warning was issued at 6 am on July 28 but is to remain valid until 7 pm.
The Met Office has said slow-moving heavy showers will affect parts of Northern Ireland on Saturday, easing from the south early this evening.
Odd rumbles of thunder are also promised, according to the warning.
Rainfall accumulations are set to reach 10mm in an hour and 30mm in a 3 hour period are likely in places, though many will see much lower rainfall amounts.