A high surf warning for the north and west shores of most isles has been extended through 6 p.m. Friday as a series of large swells builds down the island chain.

“A series of large northwest to north-northwest swells will move through Hawaiian waters into Monday,” said National Weather Service forecasters. “The overlapping pulses of swell will likely maintain surf near or above warning thresholds along affected shores most of the time through at least the weekend, with the largest swell expected on Sunday. Advisory level surf will be possible along west-facing shores of the Big Island.”

Officials warn of “dangerously large, breaking waves” rising from 18 to 25 feet to 20 to 30 feet Thursday along the north shores of Niihau, Kauai, Oahu, Molokai and Maui.

Surf along the west shores of Niihau, Kauai, Oahu and Molokai, is expected to rise from 12 to 18 feet to 15 to 20 feet.

Forecasters said this warning is in effect until 6 p.m. Friday, but will likely be extended through the weekend.

In addition to strong, breaking waves along affected shores, there will be powerful currents and navigation of channels will be dangerous.

“Stay away from the shoreline along the affected coasts,” forecasters said. “Be prepared for road closures. Postpone entering or leaving channels affected by the high surf until the surf subsides.”

Honolulu Ocean Safety, meanwhile, urged extreme caution along Oahu’s North Shore “as surf is expected to rise significantly becoming extremely dangerous and life-threatening over the next several days.”

“Lifeguards warn all those wanting to watch the large surf to remain far away from the shoreline, off of all rocky shorelines and only expert surfers should enter the water,” said Ocean Safety. “First responders ask motorists to move over immediately for responding emergency vehicles. Over the next several days, traffic is expected to be heavy in both directions between Hale‘iwa and Sunset Beach.”