As I wrote about “here”:1, a huge, powerful dateline storm blew into the northwest Pacific late last week. Storms this large create large, long-period swells (ocean waves). The period of a swell is the time interval between waves. While a lot of storms are capable of generating swell periods in the 15 to 17 second range, only large storms with strong winds can generate swell periods of 20+ seconds.

This morning the swell from this storm started hitting the west coast of North America. To see what kind of period this storm generated, I’ve included a spectral density chart for the Monterey Bay off-shore ocean buoy number “46042″:2. The spectral density chart measures the energy of the ocean waves hitting the buoy versus the frequency (the inverse of period).

This buoy sits in very deep water (1,920.0 meters), so is less prone to swell attenuation due to shoaling. That is, long-period swells are attenuated as they pass over shallow water like the continental shelf.

The area under the curve on the right of this chart represents long-period power, and in this case the long-period waves contain by far the most power (the power is a function of size and period). Most of the power is center around 20 seconds, but a substantial part of the power is in the 25 second range. Impressive.

Oh, and this is just the start. This swell will build all day (Tuesday), and will max tomorrow. With a high tide in the Bay Area tomorrow of around 6 feet, ocean front property owners should be prepared.

Zoinger says macking!

[2(Buoy 46042 homepage)]http://seaboard.ndbc.noaa.gov/station_page.php?station=46042

[1(Zoinger on the storm)]http://www.zoinger.com/words/archives/2005/12/24/dateline-mid-latitude-monster/