Maui and Molokai could see “dangerously high surf” of more than 20 feet as a rapidly building large north-northwest swell makes its way east across the islands, the National Weather Service said.

North-facing shores of Molokai are under a high surf warning through 6 a.m. today, with waves near 25 feet expected. Molokai’s west-facing shores are under a high surf advisory through 6 a.m. today with waves of 12 to 15 feet in the forecast.

Maui’s north-facing shores are also under a high surf advisory through 6 a.m. today with waves of 18 to 22 feet anticipated.

Strong breaking waves and currents can make swimming and navigating channels dangerous during this time and could also prompt road closures in areas where the waves are highest.

The swell is expected to gradually diminish and turn more northerly today, the weather service said.