HONOLULU -- Surfers on the North Shore woke up to big waves pounding on their doorsteps.

The second day of the winter season's first swell produced big surf and kept lifeguards very busy.

The powerful surf pounded the North Shore coast Friday and surfers didn't hesitate to take off on the overhead sets.

"It's like the best time of the year for us," surfer Blake Harrell said.

The big surf flexed its muscles throughout the day -- too strong for one surfer's board to handle.

Emergency crews went to Sunset Beach where a surfer suffered a minor head injury from a big set.

"On the sneaker sets that come in it will catch you and beat you all up," said surfer Clyde Aikau.

Signs warned beachgoers up and down the North Shore of the hazardous conditions.

"A lot of people just get too close to the water and when the big set comes it washes up the beach knocks," said Aikau. "You are off your feet and it drags you out."

Lifeguards rescued more than a dozen people from the water and those numbers could rise if forecasts are accurate.

"The guys are saying that El Nino is going to produce some strong swells, some consistent swells," said surfer Gilbert Lacobry.

The surf began dying out late Friday afternoon but surfers are hopeful the next is just around the corner.