Local authorities have been put on alert with torrential rain expected overnight in the south of the country.
Up to 50mms of rain (two inches) is expected to fall in the counties of Kerry, Cork and Waterford in a 12-hour period between 3pm on Saturday and 3am on Sunday.
Rain has already started to fall on the coastal fringes. It will get heavier as the afternoon progresses with the heaviest falls expected overnight.
Met Éireann overnight upgraded its weather warning from yellow to orange for the three counties.
A status orange alert is for weather conditions which have the capacity to impact significantly on people in the affected areas and is the second highest of the three.
Met Éireann forecaster Joanna Donnelly warned there was "absolutely" the possibility of flash flooding in certain areas.
She said the downpours were not directly related to Tropical Storm Harvey which has dumped record amounts of rainfall in Houston during the week. However, the same meteorological processes were in place.
She said: “This weather system has its origins in very warm tropical oceans which has a lot of moisture in it. At this time of year the oceans are probably reaching their peak. That’s what feeds the hurricanes and the deep Atlantic depressions.”
A yellow weather warning remains in place for Dublin, Carlow, Kilkenny, Louth, Wexford, Wicklow, Meath, Galway, Mayo, Clare and Tipperary.
Saturday will start off dry but heavy rain will gradually cross the country from the west and will extend to the rest of the country in the afternoon.
The warning will be in place from 3pm on Saturday afternoon to 6am on Sunday morning.
It will be bad news for those at the Electric Picnic in Stradbally but the good news is that Sunday is looking like a better day with highs of 22 degrees.
It looks like it will be dry for the big match in Croke Park between Galway and Waterford.
August was characterised by heavy falls of rain and flash flooding in many places.
The worst affected area was Co Donegal where a month's worth of rainfall fell in a few hours leaving roads impassable and bridges destroyed on August 22nd.
The statistics for August show that Malin Head weather station recorded almost twice the average amount of rain for the month. Some 172.5mm of rain fell in August. The monthly average is 95.4mm.
The wet weather has had a detrimental impact on small inspects including butterflies and bees, the National Trust in the UK has stated.
The trust said these insects thrive on sunny, dry weather, but the soggy end to the summer wiped many of them out.