Genesis
(Weather Guru)
Sun Oct 23 2005 10:57 PM
Re: Wave Heights appraoching the West Coast

Quote:

Sorry to sound ignorant, but is that red blob (implying 40 ft heights) only peak-to-trough waves or is that the storm surge (which is obviously not 40 ft but could be 10 to 15 ft with 25-30 ft waves on top)?

Edit - Not quite sure as I am not a Met. However, the data is there for us to assume something is seeing 40' wave heights.




That posted graphic link is a model, and does not include surge.

There are no working stations in the immediate area - there are two in the lower Keys, but it appears they were both damaged in September and are out of service.

Wave heights are usually given as peak-to-trough. Wave heights do not include surge, which is non-existant in deep water; it is basically "rammed water", added to by the lessened pressure (think an upwelling as pressure falls in a stick - same principle a water barometer works on.)

The only good news, if you can call it that, is that waves that are more than roughly half the height of the water under them is deep will crest and break. The reasons for this are complicated and have to do with the fact that there is "drag" on the bottom of the ocean that the wave energy runs into, which tends to "hold" the bottom of the water, causing it effectively "fall over" (develop a coamer and break)

Deep fall-offs allow wave heights to be maintained all the way up to the shore or very close to it, while shallower shelves tend to limit wave height as the shore is approached. However, whatever does reach the sthore comes in on top of the surge.

So if you have 20' waves on the beach, and a 10' surge, then the peak of the waves will be at 30' above MSL.

I would not be surprised to see 15-20' breakers on top of whatever surge that comes with it, at the eyewall and south of where it comes ashore.



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