KEEPING IT SIMPLE

Welcome to the beginner’s guide for surf forecasts. Taking the time to learn and understand the basics of how to read a surf forecast will help you piece together what you can expect when you arrive on the water. Here we take a look at what makes up a surf forecast and how to read it.

WHAT IS SURF FORECASTING? 

Surf forecasting is a collection of meteorological data that has been put through complex algorithms and swell models to predict local surf conditions in advance. 


WHERE DOES THE INFORMATION COME FROM?

All surf forecasting websites use at least some of their data from the same source. This source is the National Oceanic and Atmospheric Administration (NOAA). 

This is a US government funded service and provides the data for free, allowing surf forecasting websites to collate the data and combine it with their own algorithms and swell models. These tools allow them to display it in a way that is useful for surfers. 

The main sites are Surfline and Magicseaweed.


LEARN THE BASICS

There are a host of surf forecasting websites to choose from. A good place to start is taking a look at a few (see below), and finding one you like the look of. You should choose a site that suits you based on your location and the depth of knowledge you want from it.
 

Take look through the list below and find a site you feel comfortable with. You should find the layout easy read, even if you don’t quite understand it all yet. How each website displays its data is key to the user understanding what the surf report actually means.

Hotswell Magicseaweed Swellnet Windfinder Surfline Surf-forecast.com


HOW TO READ A FORECAST

 

KEEP IT SIMPLE

For now, concentrate on the three main areas which will provide you with the most valuable snippets of information.

1. WAVE

2. WIND

3. TIDE

These bits of information will only prove their value when you can relate what you see on the screen to what you see on the beach; so keep that in mind while you’re reading any forecast.  

Once you understand these three basics you can start digging deeper, but we’ll get to that later.

1. WAVE

WAVE HEIGHT

Not to be confused with swell height. Wave height is the average size of the waves you may expect to see at the beach.

Wave height is typically measured in feet although most forecasting sites will allow you to switch between feet and meters. 

See a separate guide where we discuss using body parts to measure wave height for easier and often more accurate wave height assessment. 

2. WIND

WIND DIRECTION

Wind direction is shown by an arrow icon. The direction of the arrow represents the direction the wind has travelled from

Learning the difference between what a favourable wind direction is (and what isn't) plays a massive role in the quality of the surf.

WIND STRENGTH

Wind strength can be just as important as wind direction. Each spot will handle various wind strengths differently. Some areas will be better suited to strong off-shores, others may be protected or sheltered at certain stages of the tide. Generally speaking little or no wind is ideal.

3. TIDE

TIDAL MOVEMENT

For each 24 hour period there are two high tides and two low tides. Understanding which tidal state suits the beach best, or favours the shape of waves you like to ride, will allow you to plan when to surf.  

Some people may prefer waves which are steeper, faster and break quicker. These waves may only occur in certain tidal states.

If you can remember surf sessions where you found the waves hard to catch, too fat and lumpy or waves that did not peal well despite ideal conditions, the tide may have been the influencing factor. 


CONCLUSION

Understanding these three basics and relating what you see online and what you see on the beach is key to managing your expectations and getting to grips with accurately reading forecasts.

RIP

rip is a flow of water out to sea

Every year 20 00 people are rescued and at least 20 people drown in rip related scenarios around the United Kingdom. The deadly nature of rip currents doesn't come from rips themselves - but lack of knowledge:

Never swim against the current. 

A rip current is a narrow channel of water that can flow hundreds of metres out to sea (that's way beyond the surf zone). As water surges up the beach with a breaking wave, it flows along the shoreline until it finds the path of least resistance back to sea. These paths of least resistance can be headlands, cliffs, reefs or gaps in beach sand banks. Once the water finds these paths, it will flow back to sea at speeds of up to 2.5 metres per second. That's over 100 metres in a minute. 

For surfers, rips are a fantastic way of getting out back (beyond breaking waves) quickly and effortlessly. For those who are unaware or unsuspected, they can be quickly dragged out to where they don't want to be. Without a basic understanding of rip currents, most people in this situation would immediately start swimming back to shore - but not even gold medallists can keep that up; and so most deaths occur because people have been swimming against the rip, without going anywhere, and tiring to the point of exhaustion. 

WAVE

wave is a pulse of energy through water

WHAT IS A WAVE

So far we've talked about tidal waves, but the waves we're most interested in as surfers are officially known as surface waves because they are formed by wind blowing over the surface of the sea. For simplicity, we'll just call them waves. 

Out at sea windy storms occur, which cause friction between the air and water molecules. This friction creates a wave that travels away from its source (like dropping a pebble in a bowl of water). The winds out at sea are very strong and blow across huge areas of water, creating waves that can travel across entire oceans. As the waves travel out from the eye of the storm, they organise themselves into well defined groups. These groups are known as sets, and this organised structure gives the waves even more power - making them perfect for surfing. 

The common misconception about these waves is that the water is flowing across the ocean. In reality, the water molecules flow in a spiralling orbiting motion within one wavelength, and this motion transports energy to the next wavelength and it's column of orbital motions. It is this energy that flows across the ocean - not the water itself. When the energy reaches the shallows, the lower part of the orbital columns are compressed; forcing them to slow down. This braking action makes the top of the wave pitch up, and when the sea depth is 1.3 times the height of the wave, it breaks - and this is where you want to be. 


WHAT IS SWELL

If there is enough time between the storm creating the wave and the wave reaching land, the waves will organise themselves into sets. For a wave to join a set, it must travel at the same speed and have the same energy as the other waves in that set. The energy and speed of waves are directly linked to the period of the swell; the time in seconds between two consecutive waves. Generally speaking, the longer and stronger the wind blows over the sea, the longer period that swell will have. 

The period of a swell can give us a lot of information. Short period swells (below 10 seconds) typically denote low energy and messy conditions. These swells cannot travel as far, as they have not had time to organise themselves into sets. Short period swells are often found in areas where the wind is still blowing strongly. This is often the situation in Aberdeen; and as you have probably seen windswell is held in pretty low regard by surfers because of these conditions. When swells travel further, the period grows longer and the wind has more time to transfer energy into the water - this means the waves will be taller when they reach shallow water.

Doubling the period will increase the height of swell by 50% - to explain this we'll use an example. If we compare two 1.2 metre swells one with a 10 second period, and one with a 10 second period. The 10 second swell will grow to almost 2 metres waves on the beach. In comparison the 20 second wave will grow to a good 3 metres on the beach. Long period swells, also known as groundswells, contain more energy, and so can travel further from the storm that created them - which increases the chance of nice offshore winds and better surfing conditions. 

To calculate the speed of most waves, multiply the period by 1.5. Using this formula, longer period waves travel faster - this also explains why big wave surfers use jet skis to catch waves. 


HOW DO SEABED & TIDE AFFECT WAVES

So, just like us, every wave is unique and breaks in a variety of different shapes and sizes. When a wave approaches shallow water, the shape of the seabed underneath has a huge impact on how the wave breaks. This is important for surfers because it can make the difference between a gentle roll and a hollow barrel. As a rule of thumb, the shallower the seabed the longer and slower the breaking form will be. On the other hand, if the seabed rises steeply, the sudden change in depth makes the wave break over a short distance with a steep face. 

This seems like a fairly easy concept to get to grips with, but in reality the seabed is full of architectural irregularities. This is where tide comes in - the depth of water often has a profound affect on how waves break in each seabed landscape. Take a flat beach with steep banks near the shore (high tide line), long and slow waves will form at low tides. As the tides approach high water the water level will rise over the steep banks, and the waves will be fast and steep. And just to confuse matters even more, I'll add in a curve ball. All waves are accompanied by strong currents that shift the sand banks of a beach break. This means that the tide:wave combination changes year in and year out - unless the break is impermeable to the changes of the sea. 

There is one type of break that is robust to the changing sea, this is a reef break. Reef breaks can be found close to shore and deep at sea. They often cause abrupt changes in the bathymetric landscape, resulting in fast, steep waves. These breaks are extremely tide dependent.  If the tide is too high, the wave may simply flow past without touching bottom. If the tide is too low, the top of the reef may be completely out of the water - making it unsurfable. This means that many reefs can only be surfed at mid-tide. 


THURSO

 

As we have discovered in stream - the seas of the Pentland Firth are notorious for their power and their danger. The infamous strait is also home some world-class waves. This is because when powerful Atlantic swell storms in  from the North West, a reef at Thurso East moulds the swell into picture perfect right hand* barrels. 

Thurso East forms waves on all tides, but it is best surfed at midtide when the barrel provides Europe's longest ride* (*with the exception of tidal river bores) - our own North Shore. 

*Just to refresh - a right hand break is a wave that breaks from left to right when you're surfing it. 


HOW DOES WIND AFFECT WAVES

So what makes waves actually surfable? The main factor is wind - i.e. the movement of air from areas of high to low pressure. When hot air rises, it creates low pressure at ground level and and wind blows in from colder areas to replace the lost air. This is seen on huge global low pressure weather systems, or closer to home in the sea breeze. 

As the sun warms up throughout the day, the land and sea heat at different rates. The sea has a greater ability to absorb the sun's warmth and it heats up and cools down at a greater rate than land. At the beginning of the day, the land is cooler than the sea, so wind blows away from the coast to replace the rising sea air. This is an offshore wind - which is ideal for clean surfing conditions. The wind blowing against the incoming waves helps prop up the face, allowing it to travel into shallower water and creates a steeper form i.e. the only reason to wake up early. 

The early morning offshore doesn't last forever, because as the sun rises it begins to heat up the land. By midafternoon the land is much hotter than the sea and this creates a low pressure over land, and a high pressure over sea. The colder sea air moves towards the coast and its lower pressure. This is an onshore wind - which often brings messy surfing conditions. Onshore winds create choppy windswell along with the original groundswell, causing waves to break sooner without letting them peel. 

As with everything, there are exceptions. If offshore winds exceed 40 kilometres per hour they deteriorate the groundswell waves. High offshore winds also mean you are paddling into the wave - which is very tiring (and usually just as cold). The one silver lining is that the lineup will probably be empty.

STREAM

stream is the horizontal motion of water

WHAT IS STREAM

Stream is the movement of water back and forth along the coast. This flow is powered by the wave that makes the tide – this can often mean that stream is misleadingly referred to as tide. If you sail you’ll often use tide for the vertical movement of water in harbours, and when you talk about tide out at sea you are really referring to stream (the horizontal movement of water). But to avoid any more confusion –we’re going to stick with stream.

Both vertical and horizontal motions of water (tide and stream) are created by the same wave flowing around the United Kingdom, and so they share various qualities. But to start with, we’ll talk about stream’s unique quality – the stream cycle. In most places with a pretty regular coastline and semidiurnal tide – the stream will flow for around 6 hours in either direction. In each direction, the stream will speed up for 3 hours and slow down for 3 hours. The direction of stream changes when the flow has slowed down and is at its weakest – this is slack water. The length (in time) of slack water is how long it takes for the tides to change.

Now we’ll look at the links between tide and stream. The biggest connection is time, slack water is always the same time before and after high tide. The time of slack water is unique to every inch of coastline, but the direction of the stream at high tide follows the tidal wave around the United Kingdom. This means the tidal stream flows north at high tide on the west coast, and on the east coast it flows south at high tide. In tidal rivers, the stream will flow upriver as the tide is rising, and downriver (out to sea) as the tide is falling.

As you can imagine, spring and neap tides can make a huge difference to stream. On springs, when the tidal range is greatest, the strongest streams occur and slack water is very quick. On neaps, when the tidal range is least, the maximum flow is much slower and slack water is longer.


HOW TO SPOT STREAM

Even on the calmest of days, when the sea is completely still, water is always moving. This is true even at slack water. Here are a few tips to spot the direction of stream.

Look out for...

Ships at anchor and buoys.

The anchor chain is usually tied to the bow (front) of boats, and when there is no wind the boat will spin around the anchor chain until it is facing the direction of flow. This is also true of fishing buoys. At slack water you can watch the boats spin around their anchor to face the new direction of flow.

pier legs and posts.

When water flows past a stationary object it creates a disturbance downstream – think of rocks in rivers. If you can see where the disturbance is, you can work out where the stream is coming from. The bigger the disturbance, the greater the speed of flow of the stream.

driftwood.

If you can grab a piece of driftwood from the high tide line, throw it as far offshore as you can and watch which direction it drifts. You can also estimate the speed of the stream by walking alongside the piece of driftwood. By counting how many seconds it takes to cover the distance, you can then work out speed.

speed = distance/time

swimmers.

If you can see swimmers casually swimming in one direction, the chances are they’re swimming with the stream. However if you can see swimmers furiously paddling in one direction, the chances are they’re swimming against the stream.


WHAT IS THE GULF STREAM

Another important stream is the Gulf, which has nothing to do with the tidal stream. The Gulf Stream is one of the strongest ocean currents on earth - it transports 150 million cubic metres of warm water per second from the Gulf of Mexico to the United Kingdom (and beyond). The Gulf Stream can be 10 kilometres wide and reaches speeds of 5 miles per hour.

The current is formed from two factors. The simplest factor is wind - southwesterly winds blow the water north towards the United Kingdom. The more complicated factor of the two is the NADW (North Atlantic Deep Water) channel. Water in the North Atlantic becomes denser because of cold Arctic winds and a rise in salinity (saltiness of the water) as icebergs form and expel the salt back into the ocean. This denser, saltier water sinks to the bottom of the seabed and flows south to the equator (the NADW channel). To keep the sea levels the same, water from the equator flows north to replace the water lost in the NADW channel. This flow of water from the equator is the Gulf Stream. 

As more icebergs melt into the ocean, the North Atlantic becomes diluted and is less saline (salty); gradually decreasing the effect of the NADW channel and thus the Gulf Stream. This means less warm water arriving to the United Kingdom, which means we'll definitely need thicker wetsuits with the progression of global warming. Without the Gulf Stream, the winter sea temperature in the United Kingdom would drop by a chilly 5 degrees Celsius.  


PENTLAND FIRTH

 

At the very top of mainland Scotland, near Thurso, there is a channel where some of the fastest tidal streams in the world can be found. This is the Pentland Firth - a narrow stretch of dangerous water between the mainland and Orkney. As the tidal wave passes around the north of Scotland it is funnelled through the narrow Pentland Firth (which - to add confusion - is not technically a firth). This funnelling generates pressure and thus the tidal stream can begin to flow at rates of 5 metres per second. 

These currents can have speeds of nearly 20 kilometres per hour and so cause eddies downstream of all the islands. As the fast flowing waters hit Stroma they are compressed and flow around the northern tip at even higher speeds. This leaves an area of low pressure on the other side of the island, and the gap is filled by water flowing upstream; creating an eddy. When the eddy meets the fast flowing stream, the contrasting currents create powerful eddlyines and the Swilkie whirlpool is created. Swilkie comes from the Norse "Svalgr", which means "the Swallower". 

Many yachts will wait for neap tides to cross the Pentland Firth as the currents can often overpower both sail and motor if there are rough seas and spring tides. The Pentland Firth also poses a threat to surfers, as the huge speeds within the straits make rip currents off the coast of Thurso, and the rest of the North East corner, particularly dangerous.

For all the challenges of the Pentland Firth, there are also valuable opportunities with green energy. The tidal power of this stream can generate 16,000 gigawatts of electricity a year with today's technology - enough to account for half of Scotland's energy consumption.    

TIDE

tide is the vertical motion of water

As the earth rotates on its axis, the changing gravitational pull from the moon powers two giant waves flowing around the coast of the United Kingdom. The distance between the peak and trough of these waves is just about 600 kilometers. When the peak reaches a beach it is high tide, and when the trough reaches a beach it is low tide. It takes around 6 hours 12 minutes and 30 seconds for the peak to reach the beach after the trough; and this is the time between low and high tides. 

The two waves begin their course around the British isles at Lands End. One wave travels north to the west coast of Scotland, over and around the tip of Scotland, then on down the east coast. The second wave travels east, up the English Channel and the two waves meet just outside London at the Thames Estuary. When there is a trough (low tide)  at the Thames Estuary, there is also a low tide in north Wales and north-east Scotland (i.e. Aberdeen). At the same time, there is a peak (high tide) along the west coast of Scotland and Yorkshire. 


HOW TO SPOT TIDE

It is extremely difficult to spot tide in just a few minutes because the water moves insidiously to the naked eye. However, there are some clues that can help you in the absence of Google or tide tables. 

Look out for...

a line of detritus. 

The high tide often leaves a visible line of seaweed, shells, driftwood and (unfortunately) plastic. Bear this in mind when planning beach cleans, a low or receding tide will be best!

sand texture.

The sand above the high tide will be rough and for the most part dry, whereas the sand in the intertidal zone is washed smooth by the receding tide. 

vertical structures.

 if you are near piers, harbours, seawalls, or cliffs: look out for marine organisms and seaweeds - the high tide is the highest point these grow at and the surface above is almost always lighter. 


WHAT IS A TIDAL DAY

There are some key timings for a semi diurnal tidal cycle (when there are two troughs and peaks a day); there is 06:12:30 between high and low tides, 12:25:00 between highs, and 24:50:00 for a full cycle. The hours represent quarter, half and full rotations of the earth and the minutes represent the simultaneous orbit of the moon. To make sense of this, you can take a step back and look at the United Kingdom from a global level.

So, first off, what makes the tide change? If you think of an imaginary line through the centres of the earth and the moon; the positions A and C experience the strongest gravitational pull – where the sea bulges out of the seabed and forms a high tide. On the other hand, positions B and C have the weakest gravitational pull – where the sea flattens against the seabed and forms a low tide. If these bulges stay in position relative to the moon, whilst the earth spins on its axis, the effect is a giant wave with two peaks and two troughs flowing around the globe.

If the United Kingdom is at position A at midnight (00:00:00) it would get to position B at 6 am and move from high to low tides. Fast forward another 6 hours, and at midday the United Kingdom will have another high tide. At 6pm the United Kingdom will have another low tide, and at midnight there will be another high tide. Or at least that would be the case if the moon stayed still whilst the earth completed one full rotation on its axis.

By the time the earth has spun around once, the moon has moved from its original position, to position X – and this means the earth has to spin for another 50 minutes before it can be realigned with the moon. This means that it takes 25 minutes to realign after a half rotation; which is why there are 12 hours and 25 minutes between high tides.

These timings are consistent in a semi diurnal cycle, but there is one main issue in this theory – land. If there were no obstacles (e.g. the United Kingdom and all other land masses) and the sea flowed over a completely smooth seabed, the tidal wave would flow as described above. However, because we have irregular coastlines and seabeds that interrupt the journey of the tidal wave, each continent and island have their own unique tides and waves.


WHAT IS A TIDAL MONTH

While the moon is arguably the most important factor in a tidal day; the sun is the most important factor in a tidal month – and this all depends on where the moon is on its 29.7 day orbit of the earth.

When the moon and sun are aligned with the earth together, the combined gravitational pull of the moon and sun is stronger, causing a greater tidal range. This means the high tides can be exceptionally high, and the low tides can be exceptionally low. These tides are called spring tides (confusingly they have nothing to do with the season of spring and refer to tides that “spring” forth with power), and happen twice a month – just after full and new moons. In springs the exceptionally low tides mean that a greater expanse of sand is exposed for longer – in some places beaches can double in size; allowing for huge beach parties to take place i.e. full moon parties.

A week after spring tides and a week before, we have neap tides. Neap (meaning without power). These neap tides happen when the moon is perpendicular to the alignment of the sun and earth’s alignment, so the combined pull is weakest. Neap tides have a low tidal range, which means that difference between low and high tides is less pronounced.

If you look at a tide table, or better yet a tidal graph, you can decipher whether you are going from springs to neaps, or from neaps to springs. Look at the heights of high and low tides over a few days – if the numbers are going towards each other you are going from springs to neaps; and if the numbers are going away from each other you are going from neaps to springs. On a daily basis if the second high tide is higher than the first you are going from neaps to springs, and if the second high tide is lower than the first you are going from springs to neaps.

Because a daily tidal cycle is 24:50:00, high tide is fifty minutes later each day – this equates to six hours later each week. This also means that each spring and neap high tide is around the same time. For Aberdeen this means on springs, high tides are almost always around 1.30am/pm (+- 50 minutes), and on neaps, high tides are almost always around 7.30am/pm (+- 50 minutes).

With this knowledge, you should be able to roughly work out the time of high tide by knowing the phase of the moon. Below we’ve added the spring and neap times (am/pm +- 50 minutes) for some of our most used surf spots:

Thurso:
Springs – 12
Neaps – 6
Peterhead:
Springs – 1
Neaps – 7
Fraserburgh:
Springs – 12 .30
Neaps – 6.30
Newquay:
Springs – 5
Neaps – 11

HOW DO WIND & AIR PRESSURE AFFECT TIDE

High and low tides are not always the height predicted in the tide table from the positions of the earth, moon and sun and their alignments. This is because the current weather conditions of the day can have a huge impact on the tide. The two main variables of this are air pressure and wind.

A low air pressure system and onshore winds will combine to create exceptionally high tides.

Low air pressure occurs when warm air rises, which decreases the pressure on the surface of the sea. A single milibar drop in air pressure can raise the local sea level by 1 centimetre. So what does a low pressure air system look like? Well, it’s pretty easy to spot – think atrocious weather and you’re pretty much there. As the air rises it also cools down, forming clouds that create wet and windy conditions.

A high air pressure system and offshore winds will combine to create exceptionally low tides.

High air pressure occurs when cold air sinks and exerts a greater force on the sea (squishing it to the seabed), which prevents the tide rising to its expected height. The weather conditions of high air pressure systems are also pretty easy to spot – think blue skies and low/absent winds i.e. a perfect summer day. If a high air pressure system happens during springs (a full or new moon), there will be extremely low tides – an offshore wind will lower the tide even more.