The Met Office has issued a severe weather warning for Northern Ireland on Wednesday.
Heavy rain and gale force winds are expected. Counties Down and Antrim are expected to suffer the worst of the weather.
Some ferry crossings have been cancelled amid warnings of south-easterly gales with gusts of up to 60mph.
The worst of the weather is expected in Counties Down, Antrim and Derry.
Roads Service said a number of trees have fallen overnight and there may also be some flooding and debris on the roads.
The Moygannon Road in Rostrevor is flooded at Moygannon Bridge. Motorists are advised to drive with extra care.
For further advice on road conditions, motorists can log onto TrafficwatchNI.
P&O Ferries said it is experiencing disruption on its sailings betweeen Larne and Cairnryan because of the adverse weather conditions.
Passengers are advised to check-in as normal, but are likely to face delays.
The company said the latest sailing information will be updated on its travel information and weather line on 0845 832 8888.
The bad weather has also led to the closure of St Colman's High School in Ballynahinch. The school has no electricity or heating.