Winters are off-season in Amalfi. Weather and temperature wise, it is mild and you can enjoy walking outside, alongside beaches admiring the views of the coast.  Having said that rains are common, and it can be chilly in the winter - although not as cold as places in the north. And these temperatures don't allow you to swim and lay on the beach.  In the winter, not all the shops and hotels will be open though. Positano will be very quiet, but Amalfi town will have restaurants and stores open.