It was raining cats and dogs.
It rained cats and dogs this morning.
We were about to get home,when it began to rain cats and dogs.
A:Hi,Cindy.I thought I'd missed you.
B:I am very sorry,Hans.Thank you for waiting for me.You must have been here for a long time already.
A:It's all right.
B:I was caught in the heavy rain,or I would have come earlier.I am sorry I kept you waiting.
A:I was in a comfortable place,so really,it's no problem.I am happy to see you.Did the rain hold you up long?
B:Yes.When I came out of the subway,it was raining cats and dogs.And I forgot my umbrella.So I had to wait for the rain to let up.
A:I totally understand.