A sneaker wave is a large wave that appears without warning, often surging up high on the beach with deadly force. Some people liken them to mini-tsunamis. Sneaker waves are a real threat on the coast, so never turn your back on the ocean and never fall asleep close to the high tide line on the beach. Keep children close to you at all times. Avoid climbing on exposed rocks, jetties and headlands during times of strong wave action.