Waves up to 40 feet high hit the North Shore on Friday, leading lifeguards to rescue 15 and issue thousands of warnings. Three men were injured on the jagged rocks between Ke Iki Beach and Sharks Cove when they were hit by a massive set.

“Honolulu Ocean Safety strongly advises people to stay off the rocks during high surf,” said spokesperson Shayne Enright. “You are risking your life.”

Ocean Safety warns that extremely dangerous ocean conditions can arise on north-facing shores throughout the winter season, which lasts until April. Unless you’re a champion surfer, be advised: Stick to beaches with lifeguards, and stay back from the water.