Reading Swell Charts: How to Forecast Surf Conditions

Whether you surf, kiteboard, SUP, dive, or spearfish, if you are serious about your sport, reading the marine forecast and swell charts will become essential to making sure you are on the water, in the right spot, when conditions are best.  At many beaches, waiting for the surf report to come out at 7am means joining 100 extra guys in a paddle battle for waves.  Understanding how to read a swell chart and come up with your own forecast will put you out in the water before the sun and the crowds.

The Basics

A wave is affected by two major factors, swell and wind.  Wind is responsible for building the wave, and also beating it back down.  In a simple explanation, when the wind blows hard across the water, it builds a swell.  This can happen when there is a very windy day at your beach, or if there is a Hurricane 2000 miles offshore, with winds blowing waves in all directions.  When the wind blows in the same direction as the swell, the waves build.  When the wind blows the opposite direction as the swell, the waves, having to travel into a head wind, get slowly beaten down and smaller in size.  Swells travel in all directions.  The key is finding a time when a swell will hit your beach, and the wind will blow offshore, or out to sea, creating nice glassy waves.

Swell Chart Resources

There are a few swell charts and websites out there that are very useful when it comes to predicting wind and swell.  Below are a list of a few we like to use: – Great Global Map of the Swell. Wind Forecasts don’t tend to be the most accurate. – This site has a great swell prediction model that is easy to read for newer surfers and riders.  Color coded red, blue, and green for choppy-glassy.  Sometimes they will miss a swell, though.  Tend to predict on the conservative side and sometimes call for a waste high glass, and it turns out to be shoulder. – By far the most accurate swell forecast we’ve found.  Only 2 day forecast for free, but when the swell is one day away, this is usually my number one way to predict how big the surf will be the next day.  Wind forecasts tend to be fairly accurate as well, but we always double check with NOAA. – Global map of links to all the Marine Forecasts for local areas.  This tends to be our most accurate wind forecast.  Thermal winds will slip under their radar from time to time, but for the most part they are great for wind forecasts up to 2-3 days out.

If you are new to water sports and monitoring the weather, you might be a little overwhelmed and not have any clue what the swell and wind numbers even mean.  So, how do you read a swell chart and make sense of all the numbers?

Swell – Heights, Direction, and Period

The first questions you have to ask are, “How big will the surf be?  Will the swell hit at my beach?  Where will it be biggest?”  For everyone, the answer is going to be different.  You’ll need to know two things before you start to look at the swell charts.  What beach or reef do you surf?  What direction does the shoreline face?

Waves will only hit certain beaches, based on the direction they are traveling.  So, if you surf at an East facing beach, you will not get any swells that have any kind of West in the direction.  In this case, west is land, giving no possibility for a swell to hit your beach from that direction.


For the sample beach, a NE, E, and SE swell will show up.  The East swell will be the strongest, will all the wave energy being directed straight into the beach.  On an East Swell, an East facing beach will have a larger wave than a SE facing beach.  And vice versa, on a South swell, a South facing beach would have a much bigger wave than an East facing beach.

Now, in the event you run into a swell that is sideshore, accurate swell heights start to get tough.  Typically a sideshore swell will generate a lot of current, and you never know how it will turn out until you look at it.  A change in swell direction of only 10 degrees could make the difference between a fun wave and an unrideable wave.

What is Swell Period or Wave Period?  Swell Period is the number of seconds between waves.  The longer the period, essentially, the fatter the wave, and more water to push you when the wave finally reaches shore and breaks.  Swell periods of 7 seconds and less are all just wind generated swells, most likely caused by a local wind or storm.  Swells of 10+ seconds tend to have much more energy when the wave breaks.  These waves are traveling from a much further distance away and tend to be a much longer line.  A rule of thumb is that if the swell height is borderline and the period is short, it will probably not be much fun for you.  But, if the period is longer, you might find the swell is a little larger than you thought!  Longer Period, Larger Wave!

The Second Part of the Equation: WIND!


The wind is typically the hardest and most critical to predict.  Most of the weather forecasts are only good for wind about 2 days in advance.  The wind changes so easily, it is very hard to predict accurately more than 48 hours out.  So, if you live along a coastline that bends and curves, wait until the day before to make the final decision on where the waves will be the glassiest.

Glassy waves are found when the wind is blowing offshore, or out to sea.  As you can see from the diagram below, an East facing beach will have glassy conditions as long as there is west in the wind.  Surfing during hard sideshore winds can be hit or miss.  Typically the current is racing down the beach, but if the wind is gusting a little more offshore for an hour, the faces will clean up.  If it switches a little onshore, you’ll be stuck in the washing machine.

Winds less than 10mph usually don’t bother the swell TOO much, though a slight light offshore breeze is icing on the cake compared to a slight 10mph sideshore breeze.   Whitecaps generally appear at 15mph+.


No matter what your sport, you’re going to need to learn to read the weather forecasts and make your own judgement call.  We all are faced with decisions every week, “Where will the biggest waves be?  Will it be glassier at another beach?”  By understanding the swell charts and what they mean, you’ll be a step ahead of the rest of the crowd, catching your share of waves before most people even have time to see the report and drive to the beach.

I hope this helps some of you all catch better waves in the future!  Enjoy it out there.

Stay Warm!

Matt Patton – www.HeatedWetsuits.Com