An approaching “giant” northwest swell has prompted officials at the National Weather Service to issue a high surf warning for the north and west shores of most islands as waves up to 50 feet are expected.

The warning, scheduled to take effect at midnight tonight and run through 6 a.m. Friday, covers the north- and west-facing shores of Oahu, Kauai, Molokai; the north shore of Maui and the west shore of the Big Island.

Forecasters expect surf along the north- and west-facing shores of Kauai and Niihau and the north-facing shores of Oahu, Molokai and Maui to reach 40 to 50 feet. Surf along the west-facing shores of Oahu and Molokai are expected to reach 20 to 30 feet, while the west shore of the Big Island is expected to reach 12 to 18 feet, according to weather officials.

Honolulu civil defense volunteers are going door to door to beach-front homes on the north and west shores to let people know about the potential danger from the surf. Groups that work with the homeless who live on beaches are also warning people that they may need to evacuate.

“It’s going to be a hazardous and dangerous environment for the next few days. We don’t want anyone to get hurt or injured, or even killed,” said John Cummings, a spokesman for the city’s Department of Emergency Management.

The city met with the Red Cross to prepare to open shelters for displaced residents, if needed.

“Residents and visitors transiting along coastal roads and highways should be careful of sand and seawater that may wash across the road.  All beachgoers along affected shorelines need to exercise extreme caution, do not enter the water or go near the ocean and heed all warnings from Ocean Safety Lifeguards and emergency personnel,” the city warned in a news release this afternoon.

On Kauai, county officials have closed north shore beaches because of the expected high surf.

The state Department of Land and Natural Resources closed the gate to the Keawaula beach section of Kaena Point State Park was closed  this afternoon.

 “If the waves are as big as projected, they could wash over the low-lying sections of Kaena Point State Park road, trapping people on the other side, and endangering anyone in the area,” said Dan Quinn, state parks administrator in a news release.  “Lifeguards will evaluate the situation tomorrow morning and advise State Parks on whether the area should remain closed,” he said.

The city is also considering closing beaches on the north shore because of the danger that beach-goers may be swept into the ocean from surf run-up.

The surf is expected to peak mid-morning to mid-day on Wednesday, but should remain at warning levels through Thursday night.

Cummings said the weather service reported that the surf expected on Wednesday is a “once in 10 year event.”

The last time surf was this big, waves caused home damage, he said.

Crews are also preparing to clear highways in case sand or debris washes over roadways.

Homeowners near Sunset Beach, where the land has been eroded by previous swells, are ready to evacuate if the surf further damages their properties, Cummings said.

“Hopefully we can get through this event. It’s too early to tell,” Cummings said.

Organizers of the Quiksilver in Memory of Eddie Aikau big wave surfing competition said the event is a “no-go” for Wednesday.

“We have taken all the time we can to assess the developments of the next big swell and it does not look favorable for us,” said event organizer Glen Moncata. “The size is there, but the quality is not, due to strong, adverse winds. We will continue to wait for the right conditions.”

A cold front is also expected to move over Oahu tonight and Wednesday, bringing unfavorable winds and rain.

Contestants, who fly in from around the world to participate in invitation-only contest, must be notified about the contest, which is why the decision had to be made on Monday on whether the contest will be held.

The National Weather Service says the cold front is expected to arrive tonight and could bring northwest winds of 20 to 25 mph, with higher gusts, and heavy rains through Wednesday morning.

The Quiksilver In Memory of Eddie Aikau is a one-day big wave event requiring wave-face heights of around 40 feet (20-foot Hawaiian-style measurements). The event was last held on Dec. 8, 2009, and has only been held a total of eight times in its 29-year history. It is only held when wave heights and surf conditions meet contest standards.

The holding period for the contest runs until the end of February.