Met Eireann has issued a thunderstorm warning for all of Northern Ireland as miserable conditions hit.
The national forecaster said that sunny conditions nationwide will be replaced with heavy rain and flooding.
The status yellow alert for Antrim, Armagh, Down, Fermanagh, Tyrone and Derry will come into force at 10am.
Despite the rotten weather, temperatures will still remain hot and humid.
Speaking on the national outlook, a forecaster said: "There'll be widespread showers today, from early morning in the southwest and in the north and by the end of the morning countrywide and becoming heavy.
"There's a chance of thunderstorms in the afternoon. It will become drier in the southwest in the early evening. Highest temperatures ranging from 15C in the southwest to 19C in the northeast with a mainly light southwest wind becoming westerly later.
"Tonight showers will merge to give longer spells of rain in through Leinster and Ulster, while it will become drier with clear weather developing in Munster and Connacht. Lowest temperatures between 7C and 11C with mostly light southwest or variable breezes.
"Tomorrow, Monday, rain will linger for a time along the north coast, with cloudier conditions there for the day. Elsewhere there'll be sunny spells and showers, the showers becoming more frequent in the afternoon. Highest temperatures 17C to 19C with mostly light southwest winds becoming variable in direction.
"Monday evening will turn cloudy on the south coast with a southeast wind picking up there. A spell of persistent rain will develop there later, spreading up through the southern counties of Leinster.
"Elsewhere will be mainly dry with clear spells for much of the night, with showers or a longer spell of rain arriving on the west coast before dawn. Lowest temperatures 9C to 11C with light variable winds becoming northerly later.
"Tuesday morning will be mainly dry for much of the country, with rain or showers along the west coast moving eastwards later. Highest temperatures 15C to 19C with light to moderate northwest winds backing westerly.
"There'll be further showers on Tuesday night with temperatures down to 11C or 12C.
"There'll be showers on Wednesday too with light to moderate westerly winds and temperatures of 14C to 18C, the showers will ease up through Wednesday evening."
