INTRODUCTION
As surfers, we quest for perfection - that elusive pristine barrel in the foreground, corduroy lines beyond; lines stacked upon one another, producing waves that break with a ceaseless rhythm that's so precise, all you have to do is take off and pull in. In this section, we provide some basic knowledge about swell formation, storm tracking and the tools to interpret various sources of weather information
Simplistically, there are two things a surfer needs to know when going surfing - wind and swell details. The speed and direction of the wind; and the size and direction of the swell. This dictates the quality of their experience. With real-time Web based models, getting this data is easy. However, there is a learning curve involved in interpreting it, whether from a barometer, a hand-drawn weather chart or fancy digital model that morphs around on your computer screen.

A storm off Cape Town. This
satellite map shows big swell
radiating outwards.

IN A NUTSHELL
The quick guide to swell formation
The air we breathe causes the waves we surf. Air has weight. Therefore, it exerts downward pressure on the ocean. Where the air is dense, there is more pressure pushing on the sea (high pressure). Where the air is rising, there is less pressure on the sea because the air is lighter (low pressure). The average pressure over the sea is about 1013 millibars. Any area where the pressure is higher than this would be a High Pressure area. Any area below that is a low pressure. Areas of low pressure can become storms. In the right conditions, these can intensify into cyclones. Areas of high pressure are often called anti-cyclones
To counteract the imbalance in pressure, air in a high pressure area (being pushed outwards as the air pushes down on the sea) moves towards areas of low pressure, where the rising air is creating a vacuum at sea level. The rising air in a low pressure sucks air along the surface of the sea to replace the air that's rising
When the air moves, wind is formed. The bigger the difference in pressure between High and Low areas, the stronger the wind. The stronger the wind, the choppier the ocean gets. The choppier the ocean gets, the bigger and quicker swell is formed. The area around a low pressure area usually has the steepest gradient between high and low pressure. It is the area where the wind is strongest, and therefore the most likely source of groundswell. When groundswell moves away from the storm, the further it travels, and the better the surf when it finally reaches land
Three variables are key to the formation of big swell: wind strength in the storm, life span of the storm and distance over which the wind blows, otherwise called "fetch". The longer the fetch, the more chance of big, deep swells forming. But to ensure deep, powerful groundswell, all three variables must be satisfied. Assuming distance and duration are sufficient, the key determining factor to swell size (and power) is wind speed. The stronger the wind, the more chance that huge swells are formed, within reason. Sometimes, really strong winds waste energy because white-capping occurs when the wind causes the steep mountainous swells within the storm to semi-break, when peaks collapse
In the storm, per square metre of ocean, Energy is proportionate to (wind speed to power of 4), while Height is proportionate to (wind speed to power of 2).

Open oceans get bigger swells, not lakes. Most land-locked lakes are limited, chiefly by the fetch. Most are not wide enough for the generation of groundswell, although you can get some pretty big, short-period swell in lakes
However, true, deep, long-period swells are the berries. Those separated by long wavelengths, containing energy that digs deep in depth, gliding for thousands of kms across the ocean in groups or "sets" of between two and 13.

This is the surfer's holy grail because, by the time the swell finally reaches shore, the waves are clean and lined up, with regular intervals between each wave, and a lull between each set. Getting close to that perfect swell.

THE DETAILS How storms are formed The earth is divided into bands of predominant pressure zones. The equator gets the most solar radiation from the sun. It's hot and humid, and the air is continually rising in a wide band around the equator. The equatorial belt is a low pressure zone, where hot, humid air rises and begins to sink on either side of it as it reaches colder altitudes The regions just north and south of the equator, where cooled air sinks to the surface are the horse latitudes, the subtropical High pressure zones. For our purposes, we'll only look at the southern hemisphere. The southern belt lies somewhere between 15 degrees South and 35 degrees South. This region surrounds the globe with a belt of denser, cooler air characterised by areas of High Pressure, where SE trade winds blow. The sinking air has completed a cycle that started when it rose from the equator, cooled and sunk down again.

Below the temperate zone - from around 40 degrees South to around 70 degrees South - lies the temperate zones, or cyclonic belt, a band around the globe where the winds blow perpetually from a westerly direction. In this region, which comprises mostly ocean, air from the temperate zones is being warmed by the ocean and is starting to rise again. As the air rises in pockets across the ocean in the form of low pressure cells, air is pulled in from the north (the high pressure areas of the temperate zone) in a predominantly NW direction and from the south (the high pressure area of the south pole, where cold polar air is sinking) in a predominantly SE direction. This cold polar air is being pushed down and outwards (northwards) from the poles with some energy, because the pole is an area of extreme high pressure, where the air is dense, dry and freezing. This polar air travels along the ocean in an easterly direction, and it feeds into the rising air of the cyclonic belt from the south side. However, the air feeding in from the North is warmer, and the contrast between the colliding temperate air and polar air often has spectacular results - the rapid and violent escalations of a storm, fed by massive columns of spiralling air spun ever faster by strong North and South flows of warm and freezing air How the storms start is a huge area of study. Warm air is constantly travelling down from the North, and freezing air is constantly moving up from the south. The cyclonic belt is the region where they meet, but it takes some event, or slight variation in climactic or oceanographic conditions to induce the spiralling ferris wheel of a cyclonic storm. Storm can form from patches of warmer or cooler ocean, kinks in air pressure at the surface, or kinks in the upper atmosphere. The jet stream, a high velocity band of air that flows West to East between 8 and 12 kms above the sea, also has an effect on the surface below, usually acting as a mirror to events at sea level. For instance, an area of divergence in the jet stream occurs when the air speeds away from a constricted, bunched up (convergent area). This accelerating air in the upper atmosphere is often the source of a surface low pressure, because the upper air starts off the momentum by sucking air up towards it from the surface In the southern hemisphere, our winter brings more swell from the Roaring Forties (the start of the westerly cyclonic belt) than in summer. In winter, the southern hemisphere is tilted away from the sun, and the band of westerly winds and associated cyclones (including the jetstream) shift further north. In summer, the hemisphere is titled towards the sun, and the storms track further south. Reading the storIf you know where high and low pressure systems are situated, and can track their movements, you can work out the direction and strength of the wind and the size and direction of the swell. You'll obviously be informed about the seasons, knowing the propensity for storms to form in the first place The barometer has been a vital tool in measuring weather. Without the aid of satellites, seafarers and coastal dwellers relied - many still do - on the barometer as a way of determining weather patterns. The barometer, which reads atmospheric pressure, could detect changes in the weather. If a barometer indicated a rapid drop in air pressure, the needle swung towards the "stormy" section, and God-fearing folks battened down the hatches. This was because a storm, or intense low pressure cell, was approaching. The faster and further the drop in pressure, the worse the weather and the bigger the swell. After the storm, the barometer would indicate an increase in pressure, with the needle rising towards the "fair" weather section. This meant that the rain would abate, the clouds would clear and the swell would subside.  Although the barometer is a great tool, there is one thing that it cannot always detect - the influence of weather that is far way, particularly the arrival of groundswell formed in the deep ocean. It can only give us readings for local conditions, which are often not influenced by sudden drops in pressure out to sea. Luckily, we have a tool called the synoptic chart that maps the movement of air pressure over wider areas. You can get updated versions of the South African synoptic chart, whether hand-drawn or computer simulated, from a number of sources on the Web (see the surf report). Most daily newspapers carry a printed version.

How to read a synoptic charTake a look at the map (right). The snaking contours lines, especially the circular clump, resembles a tattoo on a Maori warrior. The lines indicate air pressure and the numbers on the lines (isobars), are units of pressure called millibars
Millibars show the air pressure at that particular point around the pressure system. High pressure cells have a "higher" number, and low pressure cells have a "lower" number. The lines are no different to how contour lines on a topographical map show hills or valleys. The closer the lines, the steeper the gradient between areas of high and low pressure.

L - Low pressure cell       H - High pressure cell

If you understand the next few paragraphs, the doors of perception will open and all will be revealed. As discussed, gravity is behind the way air flows from High pressure (heavy air) to Low pressure (light air). Gravity exerts influence by giving weight to air. But there is another powerful force at work - the centrifugal force of the spinning earth. As you know, the earth turns on its own axis, from west to east, creating a continous, centrifugal force. 

In the southern hemisphere, this force causes high and low pressure systems to move in the same direction, from West to East. The force of the rotating earth combined with the efforts of air to move from high to low pressure causes each "cell" of pressure to spin. Winds blow clockwise around the low and anti-clockwise around the high. It so happens, thanks to those sharp folks at the weather bureau, that this direction is usually the same as the direction of the isobar lines on the synoptic chart (see pic). Note that in the northern hemisphere, these forces are mirrored, with pressure systems and winds moving in the opposite direction.

Winds spin clockwise around low pressure

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