A high surf advisory for the north and west shores of most isles has been extended through 6 p.m. today.

The National Weather Service has issued the advisory for the north and west shores of Niihau, Kauai, Oahu and Molokai, due to an ongoing, long-period, west-northwest swell.

The advisory also covers the north shores of Maui and the west shores of Hawaii island.

Surf for west shores is expected to reach 12 to 18 feet, while surf along west shores is expected to reach 9 to 14 feet.

Although the swell will gradually subside, forecasters said a fresh pulse from a shorter-period northwest swell is expected today, keeping surf elevated along exposed shorelines into Tuesday.

Surf on the south and east shores remains at 1 to 3 feet today and rises to 2 to 4 feet for south shores on Tuesday.

The advisory may need to be extended further, depending on how large the latest pulse turns out to be, forecasters said. Another long-period, west-northwest swell is expected to arrive Wednesday night.

Officials warn the public of strong, breaking waves, and strong rip currents, which will make swimming difficult and dangerous. Beachgoers, swimmers, and surfers should exercise caution and heed all advice from ocean safety officials.