The Met Office has issued a new yellow alert, warning of heavy rain tonight and tomorrow particularly in the west and over the mountains.
The Met Office said that rain, at times, and isolated thunderstorms are expected to affect the area.
“The total rain accumulation is locally, mainly over western and mountainous areas, likely to exceed 50 millimetres in a six hour period,” it said.
The warning is in effect from 5 pm on Christmas Day to 4 pm on Boxing Day.
“Be aware of the potential for localised flooding of a small number of properties, with local disruption to outdoor activities. Difficult driving conditions due to reduced visibility and aquaplaning,” it said.