ARE WAVES MADE?
Waves are formed by wind blowing over the water surface. The three
things needed to make waves are the wind speed; it's duration and
fetch (the size of the wind area). If the wind duration is more than
24 hours, the swell is fully developed and even if it blows for a
longer time at that speed, the waves will not get any bigger. If the
fetch is more than 200 miles or so, then the wave becomes fairly well
developed. If the wind blows for less than 24 hours or the fetch is
smaller than 200 miles the waves will be smaller. Lastly but most
importantly is the wind speed. The stronger the wind the bigger the
wave. Also waves made in a stronger wind will last over a longer
period of time.
TO RECOGNIZE A SWELL MAKING AREA.
On a weather chart there are high and low
pressure systems. They are separated by isobars (the lines on the
chart). If you see on a weather map an area with the isobar lines
close together and straight for more than 200 miles and the pattern is
not moving very quickly, then this would probably mean it is a good
swell making weather pattern.
How does the swell move?
Waves move away from the swell making area in 'wave groups'. If you
have winds stronger than 35 knots the waves will have a bigger wave
period and move quickly through the water. The swell will move in
roughly the same direction as the wind, but will spread out at an
angle of 15 degrees. This spreading out is why swells die out. After a
swell travels about a 1000 miles it will be half its original size.
Over 1000 miles the swell holds it size for longer.
In the above weather chart you can see that the
isobar lines at the bottom are close together and stay straight for
more than 200 miles. This is a perfect swell making pattern, with
strong winds and big waves.
AND SHALLOW WATER WAVES.
As waves pass from the oceans to the shallow continental shelf they
will change from being deep water waves to shallow water waves. This
causes a drag on the wave and slows it down. When the water becomes
less than one and a half times the wave height, it is likely to break,
which is what happens on a beach.
If a wave approaches a beach at an angle, the part
closest to the beach is in shallower water and therefore travels
slower than those further away so the whole wave front tends to be
turned into the beach. When the wave reaches the beach, it will be
parallel to it. At a headland, waves are turned towards the point and
break along its side at a much bigger size than on the beach. Also, on
individual sand bars the surf will break at a bigger size than
anywhere else. This makes ideal surf conditions.
ARE ROGUE WAVES MADE?
If there are two swells coming from different areas
they could become in sync and so the wave height becomes the sum of
the two in sync waves. Therefore two waves which are 3 feet in height
if in sync could produce a wave of 6 feet.
Read more about
CAN I FIND A WEATHER CHART?
The best source of charts is on the
Internet. There are heaps of charts to choose from. You can also get
hold of satellite pictures and weather forecasts in addition to
computer generated swell forecasts.
Check out these charts
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