Boating Course Weather
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Transcript of Boating Course Weather
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