Dr George Findlay, Cardiff and Vale University Health Board's Clinical Board Director for Children and Women, told ITV News that between six and 12 inches of water had flooded the top two floors of the Children's Hospital for Wales - and some ceiling tiles had come down with the force of the water.
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England enjoyed a winning send-off to their Australia tour as they recovered from early problems leaving Wales floundering.
Veteran singer Sir Tom, 75, is gearing up for his first concerts since wife Linda died after a "fierce" battle with cancer in April.
It will be a dry and fine day across the country with plenty of warm sunshine and light winds.