Surfing Conditions
There are a number of factors that influence the shape and
quality of breaking waves. These include the bathymetry of the surf break,
the direction and size of the swell, the direction and strength of the wind
and the ebb and flow of the tide.
Swell is generated when wind blows consistently
over a large area of open water, called the wind's fetch. The size of a swell
is determined by the strength of the wind, the length of its fetch and its
duration. So, surf tends to be larger and more prevalent on coastlines exposed
to large expanses of ocean traversed by intense low pressure systems.
Local wind conditions
affect wave quality, since the rideable surface of a wave
can become choppy in blustery conditions. Ideal surf conditions
include a light to moderate strength "offshore" wind,
since this blows into the front of the wave.
The factor which most determines wave shape is the topography
of the seabed directly behind and immediately beneath the breaking wave. The
contours of the reef or sand bank influence wave shape in two respects. Firstly,
the steepness of the incline is proportional to the resulting upthrust. When
a swell passes over a sudden steep slope, the force of the upthrust causes
the top of the wave to be thrown forward, forming a curtain of water which
plunges to the wave trough below. Secondly, the alignment of the contours relative
to the swell direction determines the duration of the breaking process. When
a swell runs along a slope, it continues to peel for as long as that configuration
lasts. When swell wraps into a bay or around an island, the breaking wave gradually
diminishes in size, as the wave front becomes stretched by diffraction. However,
it is more common to see waves cross into the shallower water and finally close
out.
Based on the underwater topography of the surf break, the
factor that most determines when to go surfing is the tide.
Wave-shape and the whole pattern of the surf changes with the tide more or
less hour to hour, while wind and swell remain constant for hours, even days.
You have to be sensitive to all these
factors to get to know a surf break, and each break is
different, since the underwater topography of one place
is unlike any other. At beach breaks, even the sandbanks
change shape from week to week. So, it takes commitment
to get good waves (a skill dubbed "broceanography" by Californian surfers). That's why surfers
have traditionally regarded surfing to be more of a lifestyle than a sport.
Of course, you can sometimes be lucky and just turn up when the surf is pumping.
But, it is more likely that you will be greeted with the dreaded: "You
should have been here yesterday". Nowadays, however,
surf forecasting is aided by advances in information technology,
whereby mathematical modelling graphically depicts the
size and direction of swells moving around the globe.
The quest for perfect surf has given rise to a field of tourism
based on the surfing adventure. Yacht charters and surf camps offer surfers
access to the high quality surf found in remote, tropical locations, where
tradewinds ensure offshore conditions. Since winter swells are generated by
mid-latitude cyclones, their regularity coincides with the passage of these
lows. So, the swells arrive in pulses, each lasting for a couple of days, with
a couple of days between each swell. If the arrival of a swell coincides with
a rising tide, the size of the waves can jump by a foot each set. Since bigger
waves break in a different configuration, a rising swell is yet another variable
to consider when assessing how to approach a break.
Wave intensity classification
Surf breaks can be grouped according to their
intensity. There are two variables to consider in determining
the intensity of a surf break: the shape of the tube and
the angle of the peel line. Tube shape indicates the degree
of upthrust, which is roughly proportional to the volume
of water being thrown over with the lip. The angle of the
peel line reflects the speed of the tube. A fast, "down
the line" tube has a peel line with a smaller angle than a slower, "bowly" tube.
Classification parameters
The geometry of tube shape can be represented
as a ratio between length and width, such that a perfectly
cylindrical vortex has a length to width ratio of 1:1,
while the classic almond shaped tube is nearer 3:1. When
'width' exceeds 'length', the tube is typically described
as "square"
Understanding a Rip Current
If you plan to surf in the ocean, knowing how to recognize and avoid rip
currents will increase your safety dramatically.
