Big Wave News

Sizing Up December 2009 on the North Shore, Oahu, Hawaii

Surfersvillage Global Surf News, 6 January, 2010 : - - Honolulu -- December 2009 surf on the north shore of Oahu lived up to the El Nino hype.  Prior to 2009, all winters of strong El Ninos and 3 out of 4 winters of moderate El Ninos have had above average number of days of high surf*, based on historical records since 1968 of daily surf observations from Sunset Beach and Waimea Bay, Oahu. 

There have only been 3 Decembers prior to 2009 over the past 41 years that have had 4 or more days of giant surf. Monster wave maniacs are taking advantage of these conditions and supporting science by helping to validate wave size.  The surfers serve as height benchmarks in photographs.   On Christmas day 2009 Garrett McNamara was captured by Eric Olson on film at Outer Log Cabins, located on an outer reef between Waimea Bay and Sunset Beach, on what is speculated to be the largest paddle-in wave ever. 

The photograph was taken from about a mile away from the nearby hillside and gave a clear view of the wave trough.  It was at low enough of an angle not to distort the size, in contrast to most helicopter shots.  

The breaker is estimated to be 60’ with a 10% margin of error. This photograph serves well to validate a formula which is used to estimate breaker size based on deep water swell characteristics.  The formula was published in the Journal of Coastal Research in 2007 bioone.org/doi/abs/10.2112/04-0397R.1 and is employed by the Honolulu National Weather Service as a guide in surf forecasting.

The formula targets zones of highest refraction, which occur on outer reefs during giant surf.  Surf heights near shore are typically about 30% lower at the highest spots.  Following the 60’ (18.3 m) depth contour off the north shore of Oahu, one sees Outer Log Cabins as a “point” or “elbow”, which causes refraction, or focusing of wave energy, creating the largest surf.  This is important to the surfer too, since the adjacent deep water provides the safety exit.

*High surf is equal to or greater than 15’ (4.6 m) peak face; giant surf, 40’ (12.2 m).  Surf height is defined as  peak face, or trough-to-crest height, at the moment of maximum cresting for the highest portion of the wave front in the zones of highest refraction (areas of highest breakers) for the average of the highest 10% of waves (H1/10), which are the common larger waves with about 5-20 minute turnaround between arrival of such groups.

www.noaa.gov

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Patrick Caldwell
Regional Science Officer,
NOAA Data Centers

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