High surf along the north and west shores of Niihau to Maui has prompted an advisory as moderate trades continue in the isles, then strengthen by midweek.

The National Weather Service has issued a high surf advisory for the north and west shores of Niihau, Kauai, Oahu, and Molokai, and for the north shores of Maui, due to a northwest swell, effective through 6 p.m. Tuesday.

Surf of 14 to 18 feet is expected along north shores, and 10 to 14 feet along west shores.

Forecasters say the advisory may need to be extended as a larger, northwest swell builds Tuesday night.

Surf along east shores subsides from 3 to 5 feet today to 2 to 4 feet Tuesday. Surf along south shores remains small at 1 to 3 feet today and Tuesday.

Today’s forecast is partly to mostly cloudy, with scattered afternoon showers and highs from 80 to 85 degrees Fahrenheit. Tonight’s skies are expected to be partly cloudy, as well, with lows dipping to 71 to 76 degrees.

Trades continue at 10 to 15 mph today and tonight.

The Hawaii Department of Health listed air quality around Hawaii island as good this morning, as the Kilauea summit eruption at Halemaumau Crater — which began Dec. 20 — enters its third week.

The lava lake within the crater continues to grow in depth as a west vent continues to erupt, and was as of Sunday night at about 623 feet deep.

Forecasters expect a brief increase in trade speeds from Wednesday night into Thursday as a stronger high-pressure system moves across the basin north of the island chain. But this boost is expected to be brief — and a change in the pressure pattern is expected to cause the trades to vanish on Friday and Saturday.