Sailors need to know about potential weather problems before casting
off. The first step for being prepared for weather problems is to
determine the weather forecast. If the forecast calls for heavy
weather, delay casting off until it passes.
There are many sources of weather information. The media provide
weather reports but the information may not be enough. It usually
is not timely nor specific to a sailor's needs.
The National Weather Service (NWS) continuously broadcasts complete
information over its network of FM weather stations. The NWS focuses
on specific locales and provides accurate marine weather conditions.
The NWS updates its forecasts as new information becomes available.
National Weather Service broadcasts can be received on inexpensive,
narrow-band, FM receiving sets. NWS broadcasts are also available on
the weather channels on VHF-FM marine radios. It is recommended that
a VHF-FM radio or a narrow-band receiving set be aboard a sailing
vessel when cruising medium to large bodies of water.
In some areas, recorded marine weather forecasts are available by
telephone. Call while preparing to cast off. Then call again just
before leaving for an updated forecast. Check with the service as
to how often it updates its forecasts.
Although it is important to know what weather to expect, it is also
important to know how to tell when the weather is changing when out
on the water. Wind is one of the most important weather elements
sailors must deal with. When the wind builds up, large waves usually
result.
Waves differ according to water depth. Wind over shallow water like
small inland lakes generate small shallow waves that are close
together and really do not pose a serious problem to medium size
sailboats. Wind over larger bodies of water like the Great Lakes
generate steep waves with short troughs which can pose serious
hazards to sailing vessels. Waves over deep water like the oceans
have more gradual slopes and the troughs are farther apart and make
for a smoother sail depending on the vessel.
To determine weather change in the northern hemisphere, it is useful
to know where the high and low pressure areas are in relation to the
vessel. Lows are a source for bad weather. Highs that are moving
toward the lows may have strong winds creating large waves and heavy
weather.
One way to locate the highs and lows in the northern hemisphere is
to implement Buys-Ballot's law. The usual procedure is to stand with
your back to the wind. Next, turn 45° to your right and the low is
usually to the left, while the high is to the right. If the low
pressure is to the west, expect bad weather.
