Gardaí in Dublin have said motorists using the M50 motorway northbound between the Red Cow roundabout and the Lucan exit may use the emergency lane due to flooding.
The Garda press office took the unusual step of issuing the traffic advice following problems in the area this morning.
Rain was heavy in Dublin and there was a significant amount of surface water on the roads, as well as flooding in some areas.
A Garda statement said: "Gardaí wish to advise motorists intending to use the M50 northbound between the Red Cow roundabout at interchange 9 and the Lucan exit at interchange 7 that the emergency lane (hard-shoulder) will be open to cars due to localised flooding in the area."
"Heavy goods and other vehicles will not be permitted to use the emergency lane but should utilise the regular lane which remains open."
There will be heavy traffic in the Drumcondra area of Dublin later this afternoon due to the Dublin v Meath match.
Traffic in Navan is expected to be heavy also, with racing taking place at the race track in Proudstown. The first race is off at 2.30pm.
There is also racing in Kerry at Listowel Racecourse, with the first race at 2.15pm and the last at 5.45pm.
In Waterford and Kilkenny, the Easy Riders charity cycle continues through a number of towns this afternoon before its finish in Clonmel, Co Tipperary.
The Garadice Lake Triathlon also takes place today at Ballinamore, Co Leitrim between 1pm and 5pm. AA Roadwatch said the routes for the event include the R202 between Ballinamore and Swanlinbar and the R199 between Ballinamore and Killeshandra.
AA urged motorists to drive with caution and to watch out for cyclists and runners taking part.
Traffic will also be heavy in Waterford, Wexford and New Ross due to the New Ross 800 - Walled Towns Vintage Car Rally. Over 130 cars are taking part. Some cars will leave Waterford for New Ross and others will depart from Wexford town for New Ross.
In Limerick, the circuit of Munster Rally takes place today around Gortnaclody, Knockawarriga and Dromtrasna Bridge.
Road closures are in place around Gortnaclody until 5.20pm, around Knockawarriga until 5.50pm and around Dromtrasna Bridge until 6.30pm, AA Roadwatch said.
The Flora Dublin Women's Mini-Marathon and the Cork City Marathon both take place tomorrow and road closures and diversions will be in place in both cities.
Met Éireann forecasts that rain in the eastern half of the country will die out this afternoon and that brighter conditions will spread gradually from the west. Highest temperatures will range from 14 to 17 degrees Celsius.
Tomorrow, early mist or fog will soon clear and all areas will have sunny spells for the rest of the day, Met Éireann said.