Swell, current, tides and weather

Subject:  Swells, currents, tides and marine weather


So, how do we go about reading a “marine weather” forecast, interpreting what is said and then figuring out when to cross the Columbia river bar, i.e. the infamous graveyard of the Pacific.  (There’s an app for that?)

Yes there are numerous apps out there including your marine weather forecast VHF radio but, you need to know a little on how to interpret the information given.

In the case of the “Western Flyer” leaving Portland and heading down to Los Angeles, California prior to getting ready to cruise Mexican waters we want to know two things:

1)  Good boating weather – that only needs to last until we make the next port and if there is a river bar present when is a good time to cross.

2)  Our first bar crossing is the Columbia river bar – how do we know when its a good time to cross?


1)  Example of a marine weather forecast:  Tonight N winds 10 to 15 knots, wind waves 2 ft, NW swell 6 ft at 11 seconds.

Gusts to 15 knots in the evening.

And since the forecast generally is broken down into TONIGHT, TOMORROW, THE NEXT DAY AND THE DAY AFTER you get a chance to read if the weather is going to be getting better or worse.

Example:  Look for what the wind in the forecast is doing, will we see more or less winds (tonight; 10 to 15 knots; by Friday the forecast shows that winds will increase to 20 to 25 knots)

Example:  Now look at the what the swells in the weather forecast are doing; tonight NW swell 6 ft at 11 seconds; by tomorrow we have a W swell 3 ft at 10 seconds with showers likely.


2)  SO WHAT DOES THIS MEAN?  3 ft at 10 seconds or 6 ft at 11 seconds – more on this later.

3)  FINDING THE INFORMATION – First get yourself one or more good marine weather resources and then get educated on marine weather.


Marine Weather Pro by AccuWeather is one of several apps that I am currently using to provide me with current weather informaton.  Live Weather app is second.   Columbia River Bar Pilots (columbiariverbarpilots.com) is an on line resource as well as Weather Underground at http://www.wunderground.com

Let’s take a look at each one separately:  

Marine Weather Pro by AccuWeather – Once I load the app and set the layers up enabling all live weathers stations and the option to long press anywhere on the map for sun rise/set I am almost in business.

There are three color icons that I can click on a map to give me a) flood and ebb tide information; tide information; floating buoys that provide information such as water temp; air temp and buoy location.

By long pressing anywhere on the map this app provides the marine forecast for the area waters – today (Monday) through Friday.

What we learn by reading this forecast are three things:  velocity of winds; height of wind waves and direction of swell.

Live Weather app – Current live weather information provided by this app is very different.

Example:  For the Columbia River Bar, 20 NM W of Columbia River Mouth, OR I see that winds are currently at 0 to 2 knots; waves are WNW 4.6 ft at 10 second period, air temp is 60.1 F, water temp is 63 F, current conditions are 59 degrees F, sunrise is at 5:48 a.m and 9:00 p.m. is sunset.  Note the differences from the forecast above.

Columbia River Bar Pilots (columbiariverbarpilots.com) –  One link takes you straight to a NOAA forecast; another link takes you to National data buoy center; another link to Tides Online; another link to the Pacific Swell chart and so on.  Lots of information but you still have to do some interpreting.

Weather Underground at http://www.wunderground.com  – I like this one because its easier to read; for example, Marine Weather for PZ 210 i.e. Southern WA and Norther Oregon coast I see a weather synopsis; by scrolling down I see the Columbia River bar information; by doing a long press on the map you get a day to day forecast from NOAA; marine weather links to nearby waters out to 60 nm and even 60 nautical miles to 250 nautical miles offshore.

By just continuing to scroll down you see open sea buoy information; tide heights for all the local areas; Tide information High/Low); keep scrolling down and you see current information which is what I am now interested in.

For Baker Bay entrance, E of Sand Island Tower, Washington Current (this is Illwaco, WA area the marina that we will be spending our second night in waiting for slack tide to cross the bar)  According to the current tidal information

Slack Flood Begins at 4:14 PM on 2014-07-21

If we want an AM crossing I see that at 6:08 AM another slack flood period begins – current speed at that time is 0.00 knots.

REMEMBER THIS:  Cross the bar only during slack water or on a flood tide

You can download an adobe pdf file titled Crossing the Columbia River bar at http://www.uscgboating.org for add’l information on crossing the bar, tides, rough bar warnings, danger areas etc.

QUESTION 1:   Good boating weather – that only needs to last until we make the next port and if there is a river bar present when is a good time to cross.

ANSWER:  Above are weather apps that we will use and where to find the information; also where to find information about when slack tide will occur.  Hope this helps.


QUESTION 2 ABOVE:  SO WHAT DOES THIS MEAN?  3 ft at 10 seconds or 6 ft at 11 seconds.

When you start reading the buoys, you’ll hear the term period.  The period of a swell refers to the time between each wave in a set (size, speed and overall condition of a swell)  If a buoy says 3 ft at 10 seconds; that means it took 10 seconds to pass between the top of the first wave (which was 3 feet) in the set and the top of the second wave in the set.

(6) six feet at 11 seconds – ( It took 11 seconds to pass between the top of the first wave (6 ft) in the set and the top of the second wave in the set.

WIND AND WAVES (From boatsafe.com)

The system called the Beaufort Scale was developed in 1805 by the British Navy.  It is a guideline that we can use for example:

Force   Wind Speed         Description      Sea Conditions                                         Waves

0                0                            Calm           Smooth like a mirror                               0

1                1-3 knots                Light Air      Small ripples                                        1/4 to 1/2 ft.

2                4-6 knots            Light Breeze       Short, small pronounced                Same

3                7-10 knots          Gentle Breeze      Lg wavelettes w/ some crests      2 ft

4                11-16 knots         Moderate Breeze   Inc. larger, some white caps        4 ft

5                17-21 knots          Freeze Breeze        Moderate, many white caps        6 ft

6                 22-27 knots          Strong Breeze        Lg waves, extensive w caps        10 ft

7                  28-33 knots           Near Gale              Heaps of waves, some breakers    14 ft

8-12            We screwed up somewhere in our forecast if we find ourselves looking at these.

In order to avoid big waves:

Avoid shallow water

Don’t go upwind in big waves

Use land as a natural breakwater

You can estimate the height of waves by knowing your eye height above the water.  If while at the top helm we are at 10 ft above the water then guess what, if you’re looking at a wave on the horizon is it bigger or smaller in height?

Watch the weather reports – Not just for one day but for the week before and after.  Know this, if the wind is 10 knots from the southwest this is good but, say if for the past week the winds were blowing 10 knots from the northeast – then the significant wave height that we will see will be double what it should normally be for the conditions.








About trawlercat

Retired and now moving on from the cruising life jeeps, adventure bike, gardening, and travel. Always in search of the next great adventure!
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