Wind blowing over water is
called a fetch, and it’s our basic
driver when it comes to swell
generation. A fetch creates wind
waves in a sea state. As these wind
waves move away from the wind
source, they start to organise and
move according to the energy
contained within them. At this
point these waves are now called
swell trains. Swell trains can
travel vast distances – especially
those with high energy content,
measured by the distance between
the swells in the swell train; i.e.
the swell period, or interval.
Long-period swells have enormous
energy moving deep within the
ocean and do all kinds of weird and
wonderful things upon reaching
coastlines and offshore reefs,
like bend around at crazy angles
(refraction) and magnify to many
times their ocean height!But, we’re racing ahead of ourselves,
and depending on where you are
surfing, period may not even be that
important.
For those coastlines exposed to
mostly close-range sources – like
the east coast of Australia, where
Coral Sea tradewind swells and low-
period Tasman Sea low pressure
systems dominate swell – swell
direction is far more important in
forecasting good surf... which isnot something you’ll hear Magic
Seaweed admit to. There tends
to be a fetish among the online
forecasters for swell period on
coastlines exposed to groundswell,
but more about swell period and its
importance later.
Let’s not bog our rails on
specifics or indulge in any romantic
fantasies that things were better
when we only had the synoptic
chart in the newspaper to forecastSWELL BASICS