In south Wales, areas badly hit by Storm Bert in November are among those now covered by the Met Office amber weather warning for rain.
With the warning valid until 06:00 GMT on Monday, the Met Office expects between 50mm and 100mm of rain may fall during this period.
In addition to travel disruption, they also warn that flooding has the potential to be a “danger to life”, that homes and businesses may become flooded and some communities could become cut off.
Yellow weather warnings for rain have also been issued more widely across the country.
Yellow warnings for rain are in place for the Lake District until 19:00 on Sunday and the southern half of Wales and southwest England until 08:00 on Monday.
Some 20mm to 50mm of rain (0.8 to 2in) could fall during the course of the warnings, with up to 100mm (4in) possible on south-facing hills. This may lead to localised flooding, travel and power supply issues.
