The Southern California
The swell model was developed by IOD/SIO scientist Dr. William O'Reilly
and is based on wave refraction-diffraction simulations
performed at the San Diego Supercomputer Center in 1990.
The model only simulates waves arriving from outside the islands (wave periods
of 8 seconds and longer).
It doesn't consider any local generation of seas.
To create the image, deep water wave data is collected by
a Datawell buoy in 549 meters of water, about 19 kilometers west of
This data is transferred to the Coastal Data Information Program at
Scripps at approximately 30 minute intervals.
The buoy data is processed to produce an estimate of the deep water
directional spectrum (shown at the bottom left of the image).
Because there is a time difference between the time the swell reaches the
platform and the time it reaches the beaches, the image is not really a
"snapshot" of estimated heights.
For a swell from the W-NW, the lag between a swell reaching San Diego after being
measured at the platform is typically around 6 hours or so, making the
image more of a short range forecast for San Diego.
However, for a south swell, the waves have hit all the Southern
California beaches before reaching the platform, making the estimates
of a south swell more of a hindcast.
Frequently asked questions
- What do Hs, Tp and Dp stand for?
Hs = Significant wave height of swell, or roughly the average height of the 1/3rd
highest waves (in feet);
Tp = Peak period of the swell (in seconds); Dp = Compass direction
from which the waves are arriving (in degrees), e.g. 180 = from the south, 270 = from the west.
- What is the circle at the bottom left of the swell image?
It's a wave spectrum (swell intensity as a function of period and direction).
It shows the relative intensity (using color, red =
highest relative energy density, or intensity),
direction (on the compass) and period (by distance from the center) of the
swell. The colors in the compass plot are not related to the
values given on color scale for Hs at the top of the image.
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