Ocean Watch

Monday, May 19, 1997

Hawaii waves variable
as they are powerful

I recently met a woman from New York who impressed me with her fitness. When we went bike riding up a steep road in the Waianae Mountains, she dusted me. A day or two later, when I asked her what she had been doing, she said, "I wanted to go windsurfing, but there was no wind. So I went jogging, then swam a mile or so at Ala Moana Beach Park."

Wow, I thought. This woman never stops.

A day or so later, however, things took a turn: The woman's Hawaii friends took her surfing for the first time, in Waikiki.

A couple of hours later, she returned to the Ala Wai Boat Harbor alone. "How did you do?" I asked her, fully expecting her to tell me she stood up and rode 50 yards on her first try.

"I didn't even try it," she said.

"Why not?"

"While we were paddling out, the waves breaking in front of my face scared me. I got so scared, I started crying," she said, wincing. "So I turned around and went back to the beach. The guys went out by themselves."

She looked out at the surf, nearly flat at the moment. "I can't believe I was so afraid."

Ah, yes, I thought, Hawaii surf, the great humbler. But I didn't gloat. Sometimes I'm afraid of the waves too.

Being leery, or at least respectful, of Hawaii's surf is reasonable. By their nature, these transfers of energy from water to air can be as variable as they are powerful.

With the exception of tsunamis, wind generates all ocean waves. At their place of origin, wind whips the water into a jumbled mass of chaotic waves.

But these waves don't stay put. Instead, they move away from their birthplace in humps of water called swells. Since long waves (measured from crest to crest) move faster than short waves, swells, as they travel, sort themselves according to size.

This sorting process is never complete, a fact easy to see at the beach where swells arrive in groups called sets. The intervals between the sets are called lulls.

Sets and lulls vary in size and frequency according to several factors: the speed and duration of the wind that created them, and the distance they have traveled, called fetch.

Water depth determines when swells become breakers. When the depth is less than half the wavelength, waves begin to "feel" the bottom. This slows them down and humps them up. Large waves feel the bottom sooner - that is, in deeper water - than short waves.

The variation in these rolling walls of water can surprise even the most seasoned old salt.

Of course, Hawaii's surf is not entirely unpredictable. We have some major clues.

During the winter, large waves arrive on Hawaii's north shores because winter storms in the North Pacific create strong winds. Large south swells occur in Hawaii's summer for the same reason: It's then winter in the southern hemisphere, and southern winter storms also generate strong winds.

Since little land lies between Hawaii and these storms, the waves created by these high winds come rolling unimpeded across the ocean until they reach our shores and break.

Calling the height of Hawaii's waves is another story. Officially, wave height is determined by taking the average of the highest one-third of waves. This method is used for channel and buoy reports.

Hawaii's surfers and other wave riders, however, measure waves on a different scale, based on local tradition. By this convention, "6-foot" surf is considerably higher than 6 feet.

After my talk with my New York friend, I glanced out to sea. Big waves were breaking outside the Waikiki reef, and several surfers were hurrying to ride them.

I see the appeal. But I also understand the fear. Some days, the best place to enjoy Hawaii's waves is from shore.