The National Weather Service has issued a high surf warning for most of Hawaii’s north-facing shores, effective from 6 a.m. today to 6 p.m. Friday.

Forecasters say a large, northwest swell is expected to boost surf to 25 to 35 feet along the north-facing shores of Niihau, Kauai, Oahu, Molokai and Maui.

Surf is expected to reach 18 to 24 feet along the west-facing shores of Niihau, Kauai, Oahu and Molokai.

The public should beware of very strong, breaking waves and powerful currents along affected coasts.

“Stay away from the shoreline along the affected coasts,” says NWS. “Postpone entering or leaving channels affected by the high surf until the surf subsides.”

The swell will likely generate advisory-level surf for Hawaii island tonight, forecasters said, then decline Friday night and Saturday.

But a reinforcing northwest swell is also due to build Saturday night, keeping moderate-sized surf in place along north- and west-facing shores through early next week.

Surf along south shores should remain small through Saturday.