A high surf advisory for the north-, west- and east-facing shores of the isles stretching from Niihau to the Big Island has been extended to 6 a.m. Friday due to a reinforcing northwest swell.

Weather officials said the swell will bring an increase in surf today across exposed north- and west-facing shores, remain elevated through this evening, and gradually decrease late tonight. Surf along east-facing shores, meanwhile, will remain high through the weekend, with the advisory likely extended later this week.

Surf is expected to reach heights of 15 to 20 feet along north- and west-facing shores of Niihau and Kauai, 12 to 18 feet along north-facing shores of Oahu, Molokai and Maui, and 8 to 12 feet along west-facing shores of Oahu and Molokai.

Surf is expected to reach 5 to 8 feet along east-facing shores of Kauai, Oahu, Molokai, Maui and the Big Island.

Expect strong, breaking waves, shore break and strong longshore and rip currents, making swimming difficult and dangerous. Beachgoers, swimmers, and surfers should exercise caution and heed all advice given by Ocean Safety officials. Boaters should be aware of recreational surfers and body boarders utilizing harbor channels to access surfing areas.

Forecasters said trades are expected to increase steadily into Friday, with locally windy conditions developing by tonight. The winds will gradually weaken and shift to the southeast on Saturday, then become light and variable from Sunday into next week as a front stalls near the islands.