Boating Course

WeatherCanadian Power & Sail Squadrons

GeneralAs 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.

WindWavesPoor VisibilityLightningHail

Wind

Wind – The atmosphere in motion. Measured in

knots for marine use (1.15mph, 1.85km/h).

Winds may be steady or gusty.

A gust is a sudden increase in wind speed

of 10 knots or more, lasting only a few

seconds.

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/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 can cause problems however.

Marine winds are greatly affected by

topography, and tend to follow the shore line.

Expect changes in the wind when

leaving protected areas or when approaching prominent

topographical features. (Local

knowledge)

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

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 1-2m waves only a mile

offshore in about 15 minutes.

Wave TrainsSignificant 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 height

One wave in about 1000 …………1.7 X sig wave height

Maximum wave …………………2.0 X sig wave height

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 hazardous to small

vessels.

Poor Visibility

Fog

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 the fall.

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.

Radiation Fog

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 FogRain 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

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

HailHail 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

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 CKWXInternet – Environment

CanadaTelephone - Recoded

MessagesVHF Radio

Forecast Regions

South Coast

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

Georgia Basin Weather Buoys and Stations

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

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 hoursForecast valid for 24

hours- updated if conditions change

“Securite, Securite” on Channel 16, Switch to WX or 21B

Synopsis and Outlook Wind Speed Terms

Light 0 to 11 knotsModerate 12 to 19 knots Strong 20-33 knots Gales 34-47 knots Storm 48-63 knots Hurricane 64 knots or more

Synopsis and Forecasts- VHF Weather ChannelsVictoria- WX 3, 21B

Strait of Georgia South Howe Sound Juan de Fuca Strait Haro Strait West Coast Vancouver Island South

Comox- WX1, WX3, 21B South End of Texada Island to Northern

Vancouver Island Adjacent Mainland

Synopsis and Forecasts- VHF Weather ChannelsTofino- WX1, WX2, WX3, 21B

West Coast Vancouver Island

Prince Rupert- WX1, WX2, WX3, 21B

North Coast, Queen Charlottes

WX 1 (162.55 MHz), WX 2 (162.40 MHz), WX 3 (162.475MHZ), 21B (161.65 MHz)

Synopsis and Forecasts- Sources

Continuous Marine Broadcast – Phone Mt. Helmcken – 250-363-6880Bowen Island/Mt Parke – 250-363-6492

Comox – South Area – 250-339-0748

Comox – North Area – 250-974-5305

Tofino – 250-726-3415

Marine Weather Information - phone Nanaimo -250-245-8899 or 8877 Campbell River -250-286-3575 Port Hardy -250-949-7148 Victoria -250-363-6717, 250-363-

6492 Vancouver -604-666-3655

Television The Weather NetworkInternet 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 21B

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 WayMonitor 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 TipsManoeuvring

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 so.

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 halo

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?

WavesAn 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.

End