Reason Ship Didn't Turn Towards Radar Image

I think this tsunami struck land that was maybe a hill and then, still at great height, went back out to sea and then struck the ship. But the captain did not know any of this, so he might have just expected the radar image to go away and that is why they unfortunately did not go ahead and start turning the ship in the direction of that image on the radar. They didn't know the wave had gone back out and was coming towards them until too late.