- Slides: 101
Boating Course Weather Canadian Power & Sail Squadrons
General As an operator of a small vessel you can not safely ignore the weather. Even an elementary knowledge of theoretical meteorology can add greatly to piece of mind, comfort, and competence while afloat.
There are professionals whose job it is to collect, analyse, and interpret weather data and to disseminate this information to users.
The object of this section is to provide a basic explanation of weather hazards and to describe marine weather forecasts and warnings, and how to obtain them.
Publications that will be useful on the British Columbia coast Marine Weather Hazards Manual and The Wind Came All Ways – Owen Lange
Mariner’s Guide – West Coast Weather Services. These publications are available through Environment Canada’s Meteorological Service
For those who wish further instruction in meteorology, the CPS Fundamentals of Weather is recommended.
This presentation is available for download from my personal web site. The address is: weathercat. ca
Weather Hazards Five Phenomena that can be hazardous to operators of small boats.
n Wind n Waves n Poor Visibility n Lightning n Hail
Wind – The atmosphere in motion. Measured in knots for marine use (1. 15 mph, 1. 85 km/h). Winds may be steady or gusty. A gust is a sudden increase in wind speed of 10 knots or
A squall is an increase in speed that lasts 2 minutes or more. Both gusts and squalls may also be accompanied by a change in wind direction.
A cat’s paw is the name given to the patches of ripples betraying the presence of slightly more wind on an almost calm day.
In a similar manner, an approaching patch of darker, disturbed water on a windy day can reveal the approach of a gust or a squall when there may be no other clue to its presence.
Only apparent wind is felt on a moving boat. This is a combination of the wind and the boat’s movement.
An example would be a wind from directly astern. In this case the boat’s speed is subtracted from the true wind speed to give the apparent wind speed.
There is a very good article on the web relating to apparent wind, you can find it at the following address: http: //johnellsworth. com/writing/nautical/understand_appwind. html
Wind without waves is usually only a problem when manoeuvring in a confined area. If a boat is well secured, it would take very strong winds to cause damage.
Sudden unexpected changes in speed or direction cause problems however. Marine winds are greatly affected by topography, and tend to follow the
Expect changes in the wind when leaving protected areas or when approaching prominent topographical
Showers may be accompanied by gusts or squalls, whether or not a thunderstorm is occurring. When a shower approaches, prepare in advance for a short period of strong and gusty winds.
Waves – Energy transferred from the air to the water. Note that the water will move at only about 3% of the wind speed.
Wind Waves – generated by the wind blowing over the water surface. Swell Waves – left over wind waves that have moved away from their source area.
Wind wave heights are directly related to the wind speed, time (duration) of the wind, and distance (fetch) it blows over the water in a straight line.
Stronger winds require shorter fetches and durations to raise the same wave, and a storm force wind can produce 1 -2 m waves only a mile offshore in about 15
Wave Trains Significant wave height is the average of the highest third of the waves Most frequent wave height……… 0. 5 X sig wave height Average wave height……………. . 0. 6 X sig wave height One wave in 10…………………. . 1. 3 X sig wave
Wind waves may be superimposed on swell waves.
Waves that oppose a current, such as at a river mouth, have a shorter wavelength, are steeper, and break more often than waves that do not oppose a current.
Waves moving into shallow water (depth less than 1. 5 times the distance between adjacent crests) also shorten and break. Both conditions may be
Fog is cloud that forms at ground level. The term is commonly used to describe any reduction in visibility.
Radiation Fog Requires clear skies, light winds and sufficient moisture, conditions most commonly found under a ridge of high pressure in
Called radiation fog because it is caused by radiational cooling. The air cools overnight and will become saturated given sufficient moisture.
The winds must be light but not calm, a bit of mixing is required to form radiation fog, otherwise the condensation will result in heavy dew.
Radiation fog is often thin and patchy and tends to form in, or flow into and fill low lying areas.
Dispersion usually begins as the sun warms the ground which then warms the air near the surface.
Advection Fog Horizontal movement of air. 80% of sea fogs are this type.
Contact with a cooler surface causes a moist air mass to cool below the dew point and fog will form.
This type of fog is usually widespread, deep and persistent. It may last for days and may not dissipate until the wind changes direction.
Frontal Fog Rain falls out of the warm air behind a warm front and into the cold air below.
When the air reaches saturation fog and or cloud will form. This type of fog will dissipate when the front passes through.
Frontal Cross Section
Lightning Electrical discharge in the atmosphere accompanied by thunder.
Lightning does not often strike small vessels and when it does, usually electronic equipment is damaged, but rarely does anything major happen to the hull or crew.
A properly grounded mast or antenna provides a cone of protection which usually extends over the whole hull of a small vessel.
A lightning strike is carried from the mast or antenna through heavy grounding wire to the keel or grounding plate, then to the water.
Cone of Protection
During a thunderstorm, stay clear of the mast or antenna, and of the wiring and rigging attached to them.
Avoid metal objects and hunch as low as possible in the centre of the cockpit or cabin.
Hail poses the same risks afloat as ashore. May do minor damage to boats if the hail stones are large enough. Can also cause eye damage if you look up when hail is falling.
Weather Forecasts Meteorological Service of Canada (MSC) produces marine forecasts for both coasts, nearshore and offshore, and for all the larger lakes of the country.
Marine Weather Forecasts Where do we find information ? How do we interpret the information ?
Weather information is available from: Television – The Weather Network AM Radio – 1130 CKWX Internet – Environment Canada Telephone - Recoded Messages VHF Radio
South Coast n n n n 03 - Fanny Island 21 - Sheringham Point 22 - Tofino 23 - Estevan Point 24 - Nootka 25 - Solander Island 26 - Quatsino 27 - Sartine Island 28 - Pine island 29 - Herbert Island 30 - Egg Island 31 - La Perouse Bank ( Weather Buoy) 32 - South Brooks (Weather Buoy) 33 - Cape Scott (MAREP Station) 61 - Chatham Point North, Middle and South Nomad Buoys not shown
Georgia Basin Weather Buoys and Stations n n n 01 - Sentry Shoal (Weather Buoy) 02 - Halibut Bank (Weather Buoy) 03 - Fanny Island 04 - Cape Mudge 05 - Campbell River 06 - Powell River 07 - Grief Point 08 - Chrome Island 09 - Port Alberni 10 - Sisters Island 11 - Ballenas Island
Georgia Basin Weather Buoys and Stations n n n 12 - Entrance Island 13 - Merry Island 14 - Pam Rocks 15 - Point Atkinson 16 - Sand Heads 17 - East Point 18 - Kelp Reef 19 - Discovery Island 20 - Race Rocks 21 - Sheringham Point 61 - Chatham Point
Synopsis and Forecasts Issued at 0400, 1030, 1600 and 2130 hours Forecast valid for 24 hoursupdated if conditions change
Synopsis and Outlook Wind Speed Terms Light 0 to 11 knots Moderate 12 to 19 knots Strong 20 -33 knots Gales 34 -47 knots Storm 48 -63 knots
Synopsis and Forecasts- VHF Weather Channels Victoria- WX 3, 21 B n Strait of Georgia South n Howe Sound n Juan de Fuca Strait n Haro Strait n West Coast Vancouver Island South Comox- WX 1, WX 3, 21 B n South End of Texada Island to Northern Vancouver Island n Adjacent Mainland
Synopsis and Forecasts- VHF Weather Channels Tofino- WX 1, WX 2, WX 3, 21 B West Coast Vancouver Island Prince Rupert- WX 1, WX 2, WX 3, 21 B North Coast, Queen Charlottes WX 1 (162. 55 MHz), WX 2 (162. 40 MHz), WX 3 (162. 475 MHZ), 21 B (161. 65 MHz)
Synopsis and Forecasts. Sources Continuous Marine Broadcast – Phone n Mt. Helmcken – 250 -363 -6880 n Bowen Island/Mt Parke – 250 -3636492 n Comox – South Area – 250 -3390748 n Comox – North Area – 250 -9745305 n Tofino – 250 -726 -3415
Marine Weather Information - phone n Nanaimo -250 -245 -8899 or 8877 n Campbell River -250 -286 -3575 n Port Hardy -250 -949 -7148 n Victoria -250 -363 -6717, 250 -3636492 n Vancouver -604 -666 -3655 Television n The Weather Network Internet n http: //www. weatheroffice. gc. ca/
ec. gc. ca/weatheradio
Marine Warnings Strong Wind Warning (20 -33 knots) Issued for Southern inner coastal waters between Good Friday and Rememberance Day. Gale Warning (34 -47 knots)
Storm Warning (48 -63 knots) Hurricane Force Wind Warning (64 knots or greater) Monitor VHF Channel 16, “Securite, Securite” Switch to WX or 21 B
Weather Procedures for Safe Boating Before Setting out: Check current weather and sea conditions by contacting other vessels in your area of interest. Obtain the latest marine forecast and warnings for your region.
Obtain tide and current information. Decide if you and your boat can navigate safely in the weather and sea conditions expected.
While Under Way Monitor Channel 16 for announcements of CCG weather broadcasts.
Periodically obtain weather information from Weatheradio Canada. Monitor the water ahead for signs of wind changes.
Note progressive changes in the sky, and monitor the direction the clouds are moving. Note changes in wind speed and direction.
Note changes in waves or swell. Recording all these observations in a log book is a good way of quickly building up a store of knowledge of your area.
Weather Tips Manoeuvring When manoeuvring in a confined area at low speeds, turning into the wind will considerably reduce the amount of room required to make the turn, compared with turning downwind.
Clouds Approaching showers may include wind gusts or squalls. Rapid building of large cauliflower-shaped clouds indicate a possible thunderstorm within an hour or
The approach of dark, rolling, threatening clouds may herald a thunderstorm within the next few minutes.
Cumulonimbus (CB) Base of the Cloud with Mammatus
Cumulonimbus (CB) with anvil top
The gradual thickening, and lowering, of clouds may foretell several hours of rain and poor visibility developing in one to three hours.
Sometimes there is also a ring around the sun or moon that is observable before the clouds become too thick.
Cirrostratus (CS) with complete
The appearance of a red sky or a rainbow may indicate deteriorating weather if it is early morning or improving weather if it is late in the day.
Wind Consider if a change in the wind was forecast, or if it is a new development.
Consider if a change in wind was caused by some topographic feature altering the flow of the air. Is the altered wind direction now going to oppose a current?
Waves An increasing swell usually indicates the presence of a large weather system in the direction from which the swell is coming, and it may be approaching.