Status Yellow rain warnings are in place for eight counties across Ireland today.
A rain warning for Cork and Kerry will be in effect until 2pm, while a separate rain warning for Carlow, Kilkenny, Wexford, Wicklow, Tipperary, and Waterford is set to be in place until 5pm.
Met Éireann has warned these counties might see localised flooding, difficult travelling conditions, and poor visibility due to heavy rain.
"Well, we are in for an unsettled spell of weather now, I'm afraid," said Met Éireann meteorologist Mark Bowe.
"We do have a nice area of low pressure sort of anchoring itself just to our west. And it is trying its best now to drive plenty of rain-laden moist air up and over us for most of this week."
He continued: "And at the same time, we do have a cooler northerly flow which is developing just off to our north. And these two weather systems are sort of meeting head-on for most of this week.
"But, of course, us nicely sandwiched in the middle. Now that means we're going to see plenty of outbreaks of rain, plenty of cloud, even some strong winds at times.
"But the silver lining is that the milder air will win out most of these head-on collisions, so our temperatures will stay on the warmer side," he added.
A very wet and cloudy morning today will bring bands of persistent rain moving north.
The rain will be heavy and prolonged, especially across Munster and south Leinster, with possible localised flooding.
A mixture of clear weather and some showers will develop from the south later in the evening, as the rain becomes confined to Ulster.
The highest temperatures today will range between 12 and 15C.
There is good news for tomorrow, as any mist or fog will clear to sunny spells on Wednesday morning, while it will turn cloudier in the afternoon.
There might still be some showers coming from the south, but it will stay mostly dry across the northern half of the country tomorrow, with temperatures between 9 and 13C.
Meanwhile, those travelling to the North might also see some travel disruption and brief flooding at places due to persistent and heavy rain.
The UK's Met Office has issued a yellow rain warning for all six counties in the North - Antrim, Armagh, Down, Fermanagh, Tyrone, and Derry - which will last until 9pm today.