The National Weather Service extended a high surf advisory for south-facing shores of all islands until 6 p.m. today.
Waves with 7- to 11-foot faces Monday will decline to 6- to 9-feet today, but will remain above the advisory level.
Forecasters say the large breaking waves create strong currents that can make swimming difficult and dangerous.
Beachgoers should exercise caution and boaters should be aware of surfers using harbor channels to get to and from surf spots, forecasters said.
A series of swells has been keeping waves above advisory levels since Thursday, delighting experienced town surfers on Oahu.
However, lifeguards have been busy with rescues and warning inexperienced swimmers.
From Friday through Sunday, lifeguards rescued or assisted 540 swimmers from south and east shore beaches.
Five men were nearly swept into the ocean near the Halona Blowhole Saturday afternoon, while lifeguards and a Good Samaritan in the water helped another group of people who were swept into the ocean by a wave at China Walls in Portlock.