Anatomy of a costal storm: January 9th 2024

 

As the winter storm season closes in on us on the coast of Washington, and on the eve of what is shaping up to be a pretty significant storm, I wanted to spend a few minutes looking back at the anatomy of a pretty interesting coastal storm that hit the coast and western and central Strait of Juan de Fuca last winter...on January 9th 2024. This one was notable to me because it was pretty damaging across the Port Angeles waterfront, and ended up shutting down Ediz Hook, a long, sand spit that forms Port Angeles Harbor that I spend a lot of time studying, surveying, and generally thinking about. 

A view along Ediz Hook NOT taken during a storm...April 2012

While Ediz Hook used to be a relatively low sandy spit one of its distinctive features now is a huge rip rap defensive breakwater on its seaward side, part of an Army Corps of Engineers Erosion Control project built in the 1970s. This rip rap raises the elevation of the seaward crest of Ediz Hook to elevations of around 9 to 11 feet above MHHW...pretty darn high...and up until this January 2024 storm I had never observed or heard of anything close to over-topping of this feature.  But this storm did it, sending water and debris over the breakwater, flooding the road that runs along Ediz Hook, and ultimately closing Ediz Hook until the storm subsided and crews could clear the road.  

Flooding of Ediz Hook on 9 January 2024

So what were the ingredients? Like most of these stories it starts with a winter high tide, predicted at about 8.5 feet MLLW, just a shade shy of highest astronomical tide at this site (coming in at 9.2 feet).  Also like most of these stories, that high tide was bolstered by a storm surge of about 1 foot, bringing the observed still water level up t 9.5 feet MLLW.  This is a high tide, but well clear of the record of 10.5 feet MLLW reached in 2003, and not even close to making the top 10 highest water levels recorded at this station since observations started in the 1970s.  

Driven by the high tide and storm surge alone, this storm was a nothing. But layered on top of this high water were waves...but interestingly the wave story has a similar narrative to that for tides and surge: The waves were big, but nowhere near record-breaking.  A wave buoy just to the west of Port Angeles, for example, recorded significant wave heights of just about 10 feet, whereas the New Dungeness buoy in the Strait of Juan de Fuca recorded significant wave heights of about 8.5 feet.  These are big waves, no doubt about it...but nowhere near maximums.  The New Dungeness buoy, for example recorded a maximum significant wave height of over 12 feet during a storm in December of 2006.  

So, like many of the impactful storms on the coast, this one was about a variety of factors coming together and co-occurring...in this case the tide, storm surge and waves.  None of those factors was necessarily extreme in isolation but taken together they created something powerful and noteworthy. This kind of interaction amongst various factors, none of which are extreme or present risks in isolation, poses real challenges in understanding these types of storms and their impacts, accurately forecasting them, and even building a sense for how likely they are to occur in the future.