A high surf advisory for the north- and west-facing shores of Ni'ihau, Kaua'i, O'ahu, Moloka'i, north-facing shores of Maui and the west-facing shores of the Big Island is currently in effect, the National Weather Service said.

Wave faces of 18 to 22 feet are expected by this afternoon in the advisory areas, forecasters said.

A high surf warning issued earlier was downgraded to an advisory.

The advisory will remain in effect until 6 p.m. Wednesday.

Meanwhile, surf along west-facing shores of the Big Island will rise to 6 to 8 feet by late this afternoon and will continue at that level through Wednesday afternoon.

A high-surf advisory for the west-facing shores of the Big Island will remain in effect through 6 p.m. Wednesday.

A powerful, low-pressure system northwest of the state has generated a large northwest swell that will arrive along exposed north and west shores today, the weather service said.

The swell is expected to build during the day and to generate the largest surf by this afternoon, forecasters said.

The swell is expected to gradually subside on Wednesday, falling to 12 to 16 feet.

Elsewhere on O'ahu today, look for surf of 2 to 4 feet along east-facing shores and less than 3 feet along south-facing shores.