Mega waves, some as high as four stories, could hit Hawaii shores today and possibly threaten beachgoers in and out of the ocean.

A huge northwest swell bringing waves with heights up to 40 feet was expected to arrive late Tuesday night and peak today, the National Weather Service warned Tuesday.

“There could be some overwash of roads closest to the ocean on the North Shore … most likely in Laniakea,” said National Weather Service meteorologist Ian Morrison. “The last swell took out most of the sand, so erosion will be high there.”

Although comparable to the last swell, this one, at its peak, will coincide with slightly higher tides, making for higher surf, he said.

Additionally, ocean water will surge and sweep across coastal areas and could damage properties and infrastructure, the Weather Service warned.

The National Weather Service issued a high-surf warning that was slated to take effect early this morning along north and west shores of Niihau, Kauai, Oahu and Molokai and north shores of Maui. West shores of Hawaii island will also be under a high-surf advisory.

Surf will rapidly build to between 30 and 40 feet this morning, lowering to 20 to 25 feet Thursday. West shores were expected to get surf at heights of 7 to 10 feet Tuesday night, rising to 20 to 30 feet today, then dropping to 12 to 18 feet Thursday.