Marine Weather

In the mid-latitudes of the Northern hemisphere, weather systems generally move from west to east. Areas of high atmospheric pressure are generally clear and without precipation, while areas of low atmospherc pressure generally include clouds and precipation.

Red Sky in the Morning, Sailor take Warning

When you view the east horizon at sunrise, you are most likely viewing an area of high atmospheric pressure area that has gone by and will likely be followed by an area of low atmospheric pressure. In which case, not a good weather forecast.

When you view the west horizon at sunset, you are viewing the atmospheric conditions that is likely to arrive tomorrow. A clear sky indicates an area of high pressure, in which case, a good weather forecast.

The primary source of Marine Weather Services in Canada is Environment Canada.

In addition to marine weather forecasts, the department also publishes a National Marine Weather Guide as well as Regional Marine Weather Guides geared to the different regions of Canada. These guides provide very valuable information about conditions that are unique to certain parts of the country.

If you have access to the internet, windy.com is an impressive site with accurate forecasts.

Red Sky at Night, Sailor's delight

Enviromental Concerns for Boaters

Fog (Visibilty)

Of utmost importance when out on the water is being able to see where you are going. Fog is one of the more significant weather hazards you will have to deal with.

Wind

When describing Wind, reference is made to the direction from where it is blowing, i.e. a west wind is blowing out of the west. In marine forecasts, wind speed is expressed in knots (nautical miles per hour) at ground level (surface winds).

Because of friction with the surface, wind velocity generally increases with altitude. The surface conditions (relative smoothness) will also have an impact on the velocity of surface winds. For example, the surface winds on open water will tend to higher that the surface winds on land. 

Green is 30 kts. (see colour scale)

If you are a sailor, wind can be fun, particularly if it is moderate and there are no significant waves. Waves are generated by the wind.

Waves

 Sea surface conditions (waves) are influenced by 4 factors;

        • wind speed

        • time (that the wind is blowing out of the same direction)

        • fetch (the distance travelled by the wind over open water)

        • depth of water

First, the speed of the wind. The stronger the wind, the more it disturbs the water surface. Secondly, the length of time the wind has been blowing out of the same direction. Thirdly, the amount of water (the distance) the wind has been blowing over open water from the same direction. That distance is referred to as “Fetch”.

The other factor impacting the sea surface is the depth of water. When waves move from deep water to shallow water, friction with the bottom slows their forward motion. As the forward motion of the waves slow, they become steeper and higher. If the water gets more shallow, the waves begin to break.

When a boater observes waves that are becoming steeper and breaking, it can be an indication of shallow water. But breaking waves can also be caused by strong winds. Breaking waves that are caused by high winds are often referred to as whitecaps. Whitecaps begin to appear when the wind speed reachs 10 knots and increases as the wind speed increases.

Lightning

Lightning is almost always associated with thunderstorms. Lightning is powerful, unpredictable and dangerous. When it comes to weather phenomena, it is also a complex topic.

From a mariner’s perspective, the concern is with a significant buildup of energy in the atmosphere looking for a place to discharge or looking for the shortest and fastest route to ground. The ground is the water that your boat is sitting in. For a sailboat, the shortest way to the water (ground) is your mast (the conductor). From the top of your mast, lightning will instantaneously find it’s way to water (ground), using the best and most direct conductors. Or in other words, the path of least resistance.

If you are out on the water in a thunderstorm, the best advice is to stay low and away from the conductors.

When heading out on the water, boaters should know what to expect from the wind.


Marine Weather Wind Warnings:

Strong Wind Warning – 20-33 kts

Gale Warning – 34-47 kts

Storm Warming – 48-63 kts

Hurricane Warning – Greater than 63 kts.


Check your local forecast before casting off.

windy.com
Wind and Waves