Wave-height reporting confusing at best, deadly at worst

Surfers far and wide understand clearly that O'ahu's North Shore waves this time of year are among the biggest anywhere. But how big?

That's the confusing part. In fact, confusion is the word most often used to describe the way Hawai'i's wave heights are calculated — especially this big-wave season, when a 10-foot wave is roughly twice the size it was last year.

"The process is in a state of confusion right now," said Rick Grigg, University of Hawai'i oceanographer and one of the first people to conquer the legendary big waves at Waimea in 1958.

"I get confused myself," said Joe Green, owner of Hale'iwa's Surf N Sea surf shop as he tried to gauge the size of a typical North Shore wave yesterday.

"That's about 5 feet," he said. "That's local size. Of course, if you measure the face of that wave, it's an easy 10 feet from the pit."

So, is it a 5-foot wave or a 10-foot wave? It's both, depending on how you measure it. And that fact has some safety experts worried.

This year the National Weather Service has tried to make the measuring process more uniform by strictly reporting waves by what's known as their face value — meaning the height of the face of a wave.

Trouble is, the people who feed the numbers to the service report heights that are "all over the map," said Bob Burke, a meteorologist for the weather service in Honolulu who trained O'ahu lifeguards in the accurate reporting of wave heights.

Burke said he met resistance from those who are used to reporting local-style wave measurements, which in general are half the height of face value and are figured in a cryptic manner.

Safety vs. local custom

Before this year, the weather service reported local-size and not face value. For example, a 10-foot wave reported last year would be approximately a 20-foot wave this year, although Burke said the larger the wave the less the disparity.

"We're currently going through a learning curve," said Roy Matsuda, lead forecaster for the weather service. "I'm sure it will get better as the numbers are more consistent. But we are all in a bit of confusion right now."

Said John Cummings, public information officer for O'ahu Civil Defense: "We're aware of the problem and we have been able to work around it. We work directly from the National Weather Service figures, and the weather service is always fine-tuning."

Surf forecaster and UH oceanographer Pat Caldwell said the situation pits real safety issues against the local custom of under-reporting the size of a wave.

"I call it local scale," said Caldwell, whose own forecast Web site lists face value wave predictions as well as local scale, which he logs at exactly half the face value.

Grigg says 40 years ago all O'ahu waves were measured at face value — "from top to bottom, up and down.

"Then, lifeguards began underestimating because it was cool to say a 6-foot wave was 3. Then, surfers started doing it."

Soon, surfers realized that if they understated the wave size, fewer surfers would show up, said Grigg. That reinforced the practice. When people questioned how a 10-foot wave could be a 5-foot wave, Grigg said, "the surfers thought and said, 'We measure them from the back of the wave.' "

Both Grigg and Caldwell say a wave's height can't be measured from the back.

"That was just an attempt to make sense out of something that didn't make sense," said Caldwell. "A way for someone to justify an illogical system."

All of which is academic. The trouble, according to the experts, is that many tourists don't know local from face value and are not aware of the local measuring system. So, they hear about 3-foot waves on the North Shore and head for the famous, though dangerous, waters.

"We've had some serious accidents because tourists went out there and broke their necks," said Grigg. He blames the local surfers.

O'ahu lifeguards, caught in the middle, are the best in the world, Grigg insists.

Burke said initial lifeguard resistance tended to fade once he pointed out the seriousness of the matter and that the weather service's forecasts aren't merely geared for local surfers.

"When you bring up the safety issues, that gets their attention," said Burke.

More art than science

Jim Howe, the state's chief of lifeguards, said the idea of face value being accurate is subjective.

"All of this talk about wave size does not give an accurate depiction of what happens at surf spots around the islands," said Howe, who added that lifeguards have no tools to measure waves.

What can be measured accurately is the swell, said Howe. But the swell creates different wave breaks, so the lifeguards are in the position of trying to figure out what to report, he said.

The bottom line, he said, is that the wave's measurement is still open to opinion.

Caldwell acknowledged that measuring waves is more art than science.

"It's kind of a fuzzy value because along any given wave front the height will vary in size," he said. "Waves have different breaking characteristics that affect the measurement."

Those who want to guess a wave's height can get a fairly accurate idea by measuring the face of it in proportion to the general height of the person riding it, he said.

For newcomers and those unfamiliar with the North Shore's treacherous breaks, the measurement that matters most is the distance between the waves and the safest spot on shore, Caldwell said.

Reach Will Hoover at whoover@honoluluadvertiser.com or 525-8038.

Correction: Jim Howe's name was misspelled in a previous version of this story.