There were huge downpours in several parts of the county, with Inishowen the worst effected.
“There is a risk of spot flooding in many areas,” said a Met Eireann spokesman, “but particularly over County Donegal this afternoon and evening.”
The downpours followed similar events in Belfast, Dublin and Cork last night this morning.
Play was suspended at the Irish Open in Portrush, Co Antrim this afternoon after a lightning warning was issued.
More than 26,000 spectators are at the event where the weather warning was issued.
Stars like Rory McIlory and Darren Clarke had to run for cover and return to the club house.