Met Eireann has issued a Status Yellow warning for heavy rain, with "thundery downpours" and "spot flooding" expected.
The alert was issued just after lunchtime and will be in place from 2pm until 8pm on Saturday.
The caution is in place for Carlow, Kilkenny, Wexford, Wicklow and Waterford, with up to 30mm of rain expected.
It comes after the national forecaster predicted a very wet weekend, with no sign of summer returning anytime soon.
And despite the warning expiring tonight, the long showers look set to continue for most of the day on Sunday.
A Met Eireann forecaster said: "Becoming widespread and heavy or thundery during Saturday afternoon. Maximum temperatures of 16C to 19C, in light to moderate westerly winds.
"Tonight will be mostly cloudy with scattered showers most frequent in the west, drier overall in the east and southeast. Lows of 10C to 12C in mostly moderate southwest winds.
"Sunday will be mostly cloudy with scattered showers to start the day in the east but drier clearer conditions in the west will extend east through the morning.
"Cloud will however increase once again in the west during the late afternoon with rain developing on Atlantic coast by evening. High temperature of 15C to 19C in moderate to fresh westerly winds.
"Rain in the west will extend eastward across much of the country overnight with occasional heavy burst."
Things will get better on Monday, as the rain begins to clear throughout the day, bringing some dry spells and temperatures of 21C.
Tuesday and Wednesday will be unsettled again, with temperatures expected to drop.
Early indications predict more heavy rain, particularly in the west, as the week goes on.
