Surf of 20 to 30 feet on the North Shore is expected to rise to 35 to 45 feet tonight, raising fears that waves will wash across roads and damage coastal properties.

Volunteers from the Honolulu Department of Emergency Management will monitor highways on the North Shore during tonight’s high tide between 9 p.m. and 11 p.m., said Mel Kaku, the director of the Department of Emergency Management.

The National Weather Service said the peak of the swell will coincide with the high tide tonight and north winds, which could push the surf farther inland.

In addition, the swell was generated about 1,000 nautical miles north of Hawaii, relatively close to the islands, which means the waves will be closer together and more likely to run up on shore.

No major problems had been reported by this afternoon, Kaku said.

If the surf comes over the highway, the city volunteers will call the state Department of Transportation and crews will be dispatched to clear the roads, Kaku said.

If necessary, Honolulu police could close sections of the highway, he said. If that happens, police will notify the public through the Nixle text messaging system.

The volunteers will go out again during high tide Wednesday morning at about 9:40 a.m., Kaku said.

A high surf warning is posted for north and west facing shores of Kauai County, Oahu and Molokai and north shores of Maui until 6 p.m. Wednesday. North and west shores of the Big Island are under a high surf advisory.

Forecasters said west shores of Oahu and Molokai should see surf of 15 to 20 feet today rise to 20 to 30 feet tonight.

“Expect ocean water surging and sweeping across beaches, coastal benches and lava flows creating the potential for impacts to coastal properties and infrastructure,” the weather service said. “Large breaking surf, significant shorebreak and dangerous currents make entering the water very hazardous. Anyone entering the water could face significant injury or death.”