Cool temperatures are in the forecast for most of the Hawaiian Islands while large surf is expected for the smaller islands through Wednesday.

A high surf advisory has been issued for the north- and west-facing shores of Niihau and Kauai, effective from noon today to 6 p.m. Wednesday.

Weather officials said a new, long-period, northwest swell is expected to spread down the western end of the island chain starting this morning. The swell, combined with increasing northerly winds, will cause rough surf to build along north- and west-facing shores of Kauai County by this afternoon, rising to high surf warning criteria by late Wednesday.

Surf is expected to reach 15 to 20 feet tonight, and 10 to 24 feet late Wednesday afternoon along the north- and west-facing shores of Kauai and Niihau.

Expect strong, breaking waves, shore break, and strong rip currents, making swimming difficult and dangerous.

Beachgoers, swimmers and surfers should exercise caution and heed all advice given by ocean safety officials. If in doubt, do not go out.

A wintry mix of ice and snow, meanwhile, is expected above the 12,000-foot elevation level on Big Island summits, prompting a winter storm watch from 6 p.m. this evening through 6 p.m. Wednesday.

A high wind warning is also in effect for Big Island summits from 6 p.m. this evening through 6 p.m. Wednesday, with west winds increasing to 55 to 65 miles per hour, and localized gusts over 80 miles per hour, tonight and Wednesday.

Anyone planning travel to the summits should consider postponing their trip until improved weather returns, weather officials said.

Forecasters, meanwhile, say a strong, upper-level disturbance is expected to pass through the isles tonight and Wednesday, bringing a slight chance for thunderstorms and the potential for locally heavy rainfall to Maui County and the Big Island.

Tonight is expected to be breezy, and partly cloudy with isolated showers in some areas. Overnight temperatures will dip into the mid-50s to mid-60s range for most parts of the isles.

Moisture associated with an old front is expected to shift east of the state Wednesday night, followed by cool, brisk northerly winds spreading over the isles through late in the work week.