A high surf warning has been issued for the “giant” swell arriving tonight for portions of Hawaii.

The National Weather Service expects surf to reach 40 to 50 feet along most north-facing shores late tonight through early Wednesday. Surf for west-facing shores is expected to reach 25 to 35 feet.

The warning — in effect from midnight tonight to 6 p.m. Thursday — covers the north- and west-facing shores of Niihau, Kauai, Oahu, and Molokai, and the north-facing shores of Maui.

Forecasters say the “largest swell of the season” from the northwest is expected to move through, with surf rapidly building late tonight, exceeding warning levels, then peaking through Wednesday. The swell is expected to remain above warning levels through Thursday.

The warning is expected to expand to the shores of Hawaii island later today or tonight.

Officials warn that impacts will be very high, with ocean water surging and sweeping across beaches, periodically overtopping vulnerable coastal roadways.

During a high surf warning, the public can expect significant beach erosion, along with wave runup which will impact coastal properties and infrastructure, especially during high tide just before daybreak.

Additionally, the public should watch out for powerful longshore and rip currents, along with surges inside exposed harbors, which can cause damage to boats.

“Stay away from the shoreline along the affected coasts,” officials said. “Be prepared for road closures. Postpone entering or leaving channels affected by the high surf until the surf subsides.”

A small craft advisory is also in effect for all waters from northwest of Kauai to windward Maui County, due to seas of 15 to 20 feet, from midnight to 6 p.m. Thursday.