The National Weather Service has issued a high-surf advisory, effective at 6 a.m. today, for the north- and west-facing shores of Ni'ihau, Kaua'i, O'ahu, Moloka'i and Maui.

The advisory will be upgraded to a high-surf warning as of 6 p.m. today, forecasters said, with the warning expected to remain in place through 6 p.m. Sunday.

A large swell out of the northwest will produce advisory-level surf today and is expected to continue to build throughout the day and tomorrow, leading to warning-level surf by tonight, forecasters said.

Wave faces along the north-facing shores of the affected islands are expected to reach 10 feet to 16 feet today and continue climbing overnight, exceeding the 25-foot north-facing shores warning level by Saturday morning.

Surf along west-facing shores is also expected to build, resulting in wave faces approaching the 20-foot warning level by Saturday morning.

A high-surf "advisory" means that high surf will affect beaches in the advisory area, producing strong rip currents and localized beach erosion.

A high-surf "warning" means that dangerous, battering waves will pound the shoreline, resulting in very dangerous swimming and surfing conditions and especially deadly rip currents.

Elsewhere today on O'ahu, look for surf of 3 feet to 5 feet along east-facing shores and 1 foot to 3 feet along south-facing shores.