Sunday, August 16, 2015

The Art of Sea Kayaking: Forecasts

This is part of a series of posts covering what it takes to paddle on the open ocean, exposed to swell and away from easy landings. I'll discuss the techniques and ideas I feel are important to understand in order to safely paddle in such a dynamic environment with the focus on how to approach thing instead of simply how to do things. While my intention is to help guide folks who are newer to the sport and possibly neophytes on the ocean, I hope some of the wisdom I share gives even the most seasoned paddler more to think about. This is not meant to teach any specific skills, but rather to inform people on what they should be learning and give some suggestions for going about it. Many of these things are covered in typical classes (some are not), and I highly encourage instruction from a skilled teacher. But I also know many paddlers learn through experience - properly so - and hope these concepts will lead to better learning experiences.

There's a sequence to these posts for a reason, so if something seems unfamiliar try starting at the beginning. Make sure to read the disclaimers and warnings in Part 1: Introduction. And feel free to ask any questions or share your own thoughts in the comments.

Part 2: Technique
Part 3: Rescues and Rolling
Part 4: Surf Zone
Part 5: Forecasts
Part 6: 
Part 7: Seamanship
Part 8: Working With the Water
Part 9: Rock Gardening


The Theory

Weather. Like it or not, you have to deal with it. While forecasts may not be perfect, these days there is a ton of information easily available to paddlers to help them anticipate conditions and be prepared for the worst. Most people do check the weather before they go paddle. They might even check the marine forecast if they live on the coast. But there’s a lot of information packed into those quick little descriptions and most people don’t really know how to interpret it. Let’s start by breaking down the basic information you want to have and then look at where to find it and how to use it. There’s a list of useful links at the end if you want to jump right to that.

Of all the weather factors, wind has the greatest effect on kayakers. For most marine forecasts wind speed is given in knots (kt) and normally in a wide range, like 10 to 20 kt. First, you have to know what knots means, otherwise the forecast is useless. A knot is a nautical mile per hour and a nautical mile is a little longer than a statute mile – what we use on land. That makes knots a little stronger. 1 kt = 1.15 mph. So 10 kt is about 11 mph and 20 kt = 23 mph. What does that wind speed mean to you?

You need to correlate a certain speed of wind with its effect on you as a paddler, and the best way to do that is after your paddle. When you get home from your local lake or bay paddle, look up what the winds were and start to equate the numbers to the experience. Did you have trouble with the wind? Was it annoying but tolerable? Did it force you to turn around? What did the water look like? We all have a general sense of what a strong wind is, but we can’t necessarily place a number on it. It’s time you learn how to do that.

10 kt of wind is a nice breeze but won’t affect your day much. 15 kt is enough to slow a kayaker down. Many paddlers have trouble making headway into a 20 kt wind (and there’s going to be whitewater everywhere). That means a forecast like 10 to 20 kt has a big range and you have to be ready for the high end.

It also makes a big difference which way that wind is blowing. Of course it’s much easier to paddle with the wind, but your chosen route might not give you that option. If you start out with the wind, you’ll have to fight it on the way back – and what if it gets stronger? If you head into the wind at the beginning you’ll be able to turn around if it gets too strong. Onshore winds are most common but offshore winds can be dangerous because they’ll literally blow you out to sea.

But it’s not just the wind’s effect on you that’s important. You need to know and prepare for what it will do to the ocean. Whitecaps start forming a little over 10 kt. At 20 kt there are breaking waves all over the place. The windwaves – the shorter, steeper waves that stack ON TOP of the swell – will be 2 to 4 ft. Even if you’re running with the wind, it will be a bumpy and chaotic ride.

Just how rough also depends on how long the wind’s been blowing and from what direction. It takes time for wind waves to build up, so if there has been a 20 kt wind for three days straight it will be rougher out there than if it’s been building during the day and falling overnight (common along coastal areas). It also depends on whether it’s blowing in off the open ocean where it has more water (called fetch) to build up or if it’s blowing out to sea, in which case the waters nearest shore will be somewhat protected.

Time and experience, along with a little observation, will tell you what different wind speeds really mean to you personally. You need to know that before you can use any forecast to make decisions. And while there’s a lot to consider about the wind, the swell forecast is also more complicated than it first appears

Let’s start with the ‘easy’ part: wave height. For NOAA forecasts, the height is measured from the peak of the wave to the trough of the wave (if you’re a physicist like me, that’s twice the amplitude). Four feet may not seem big, but if you’re sitting in your kayak at the bottom of the swell then the peak of the wave is over your head. It’s also an average, so some waves will be bigger and some smaller. And it’s the forecast for the swell out in the ocean – what the surf is doing on shore could be vastly different.

The period of the wave is actually one of the most important parts when trying to predict the size of the surf. Technically, the period of a wave is the time between one peak and the next, usually measured in seconds. More practically, it’s the length of the wave. That matters because when a wave breaks on the beach (or your head if you’re sitting in the wrong place) the volume of water that comes crashing down depends on both the height and the length (think of it like a box: a tall, skinny box doesn’t hold as much as a medium, wide box). A fifteen second period wave will have about twice as much energy as an eight second period wave. That also means that the wave will jack up to a lot taller than four feet when it breaks (because of all that extra water in there). So the size of the surf will often be much larger than the size of the swell, and the longer the period the bigger it will be.

But all that depends on the direction. Many beaches are partially shielded by points of land or reefs. If a beach is protected from the direction the waves are coming, it might actually have little to no surf at all. By choosing the right beach, I’ve launched on twenty foot days with only little ankle-biters to contend with. And I’ve had some great surfing with 2 ft at 18 second waves.

Another thing to consider is that swells come from long distances, often storms thousands of miles away. It might take two weeks for the energy from a typhoon in Japan to hit the west coast of the U.S. At the same time, we might also be getting a swell from last week’s storm off Mexico. We often have two different swells, sometimes more, arriving at the same time from different directions. These mixed swells will create more variability in a system, often longer lulls and then bigger sets out of nowhere. A beach protected from a NW swell might be exposed to a S swell.

Finally, the NOAA forecast often lets you know if there’s some weather that could affect mariners. Fog is a common one. Rain is listed as well. While a little water in the sky doesn’t affect kayakers that much, fog can be a big deal. Losing sight of land can lead to disaster if you aren’t prepared, so always be prepared for fog.

Slightly related but a different topic, you should also look up any relevant currents and tides. Many coastal areas don’t have significant currents, but any place with islands, channels, or restricted passages can have currents that completely change the game. Low and high tides mostly affect where you can land and launch – and how much mud you’ll have to slog through to reach the water. Both tides and currents can be looked up ahead of time, but do keep in mind that they are also predictions and the real conditions can vary significantly. Tide predictions are often affected by weather in general and snowmelt rates in particular near river mouths and estuaries, and changed tides equals changed currents.

Getting back to wind and waves, those are the basic concepts. Now let’s take a look at an actual forecast and how you might want to use the information.

The Practice

National Weather Service Marine Forecast

238 AM PDT FRI AUG 14 2015      

  PZZ455-141645-  CAPE MENDOCINO TO PT ARENA OUT 10 NM-  238 AM PDT FRI AUG 14 2015    

A few technical notes before we dig in. This particular forecast covers an area almost seventy miles long and ten miles out to sea. That’s a lot of ocean and it’s not all going to have the same weather. Some areas will be worse and some better. It takes a while to get a sense of how a specific area relates to a general forecast. Until then, err on the side of caution and assume the worst. You might also notice the ‘Small Craft Advisory’ in this forecast. The standard for that varies by region. It’s normally waves over ten feet and winds over 20 kt. We don’t have that here but we get the advisory anyway, probably because it’s summer and people are used to milder conditions and more non-locals are likely to be hitting the water. Like everything else about these forecasts, it takes some time and experience to interpret what appear to be simple numbers and statements.

The forecast for TODAY starts with the typical NW winds 10 to 20 kt. I probably see that more than anything else here in California. As mentioned above, the 10 to 20 range covers a lot of different wind. The NW is the direction the wind is COMING FROM, again our usual here in CA. This could mean a relatively mild day or it could mean a fairly rough day. The general description talks about a building high pressure and steep waves. Combine that with a small craft advisory for the following day and I think a rough day is more likely so I’d plan for that. But it’s vague enough that I’d want more data.

We normally paddle much closer to shore than ten miles out, so our wind is often closer to what coastal towns experience than what the marine forecast calls for. The forecast for the town of Mendocino called for 12 mph winds. If I were planning a paddle, I’d look to stay near shore and start out heading north.

Another great place to get more detailed wind forecasts is from sailing sites. Sailors obsess over winds the way surfers obsess over waves, so a good sail forecast will be much more detailed in both location and timing compared to a general mariner’s. These are often location specific so do a google search for winds and sailing in your area and see what you can come up with.

But let’s move on to the waves. The swell for TODAY is waves NW building to 4 ft at 11 seconds. As with the wind, the direction, NW, is the direction the waves are COMING FROM. Building says that the swell is increasing – important to know that whatever it looks like in the morning it is expected to be bigger later on. 4 ft is the height of the swell – but not necessarily the surf. 11 seconds is a moderate period (7 or 8 is short, 20 is really long).

One important thing to note is that the swell is predicted to increase overnight and into the next day. Generally larger waves travel faster than smaller waves, so quite often when the swell is building you’ll find that some of the larger sets hit much earlier than the main swell. In this case, there’s a good chance you’ll have a few 6 ft waves TODAY and some 8 ft waves hitting TONIGHT. Be prepared for those outliers.

There’s also the S swell that is forecasted for TONIGHT. 2 FT is pretty small, even at 12 seconds, but it’s enough to change the dynamics on the beaches or areas that are protected from the NW. It also adds to the overall variance in size of waves. If you were out rock gardening, it would mean you should spend a little extra time watching features before you commit yourself. Every ten minutes, every twenty minutes, you’re likely to get some waves significantly bigger than usual.

For my area, this is a relatively small swell from a typical direction. Some surf sites might be working, lots of rock gardening will be possible. Before I chose my location I’d like a little more data.

This time our surfer friends come through. Their sites and forecasts almost always give us what we really need for the swell: exact direction and surf height. NW is pretty general, and some breaks work when it’s more westerly and some when it’s northerly. Surf sites will often break down swell direction into degrees, so instead of simply saying it’s from the NW, they’ll tell you it’s from 278 degrees. That’s a lot different than 321.

They also tell you the size of the surf, which is important if you plan to launch or land from the beach. It will let you know if that long period component is going to make the waves big near shore. Keep in mind that each beach is different so small surf at one beach in the forecast doesn’t mean it will be small everywhere. If you can’t find a surf forecast for your exact beach, look for a nearby one, but more importantly – look for one facing the same direction.

For all of this, keep in mind that forecasts are just someone’s best guess of what will happen. Some are more reliable than others, but they all have errors. One good thing to get in the habit of doing is to look at the actual conditions at the moment. Look at buoy data to see what the swell is doing. Look at wind readings to see how it’s blowing. If a forecast called for a small craft advisory starting in the afternoon, but you see that it’s already 20 kt with 6 ft swell at 8am, you can be sure that the heavy weather is already here. On the other hand, if I’m headed out for a short paddle and the wind is currently calm down at the beach, I might try to rush out and get my time in before it hits.


All of this is really for day paddles. If you’re going on an expedition where you’ll be out for days or weeks at a time you’ll need a much better sense of weather patterns for an area and how to draw conclusions with minimal information. These days, some of the big-time expeditioners use satellite communications to stay in touch with a weather researcher back home who puts together all the info and creates a specific forecast for their route. You don’t have to go that far, but it doesn’t take much to look up a few sites and know how to interpret the information there.

Get used to looking up forecasts before you go. Many disasters have started with kayakers on a beach deciding things look fine at the moment even though the prediction is for things to deteriorate. You make your go/no-go decisions based on the future, not the present, and you always consider the high side of the forecast, not the low. It will save you time, make your paddling easier and more fun, and keep you safer.

Useful Links:
Wind Forecasts: Sailflow; Intellicast 
Surf Forecasts: Magic Seaweed; Surf-Forecast
California Resources: BASK Trip Planner;

Got any great forecast resources? Share a link in the comments!

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