Meteorology
Weather Information
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Anyone taking a boat to sea should have some insight into what the weather is going to do. It is unwise for a sailor to rely totally on the Shipping Forecasts prepared by the Met Office and broadcasted by the media.

These forecasts cover huge areas and are thus bound to be general, rather than specific. A sailor should supplement this broad picture with more detailed local information. For current times of all forecast sources available in your region outlined below, consult the National Press.

Local Conditions - Sea Breeze

In local weather conditions, especially during the summer months, much of the coastline experiences sea breezes. The heat of the sun warms up the land, which causes the air above it to warm up and rise. Cooler air from above the sea is drawn in to replace it. (see diagram)

This sea breeze usually starts during the late morning and reaches its peak in mid-afternoon. One of the telltale signs of a sea breeze is the line of cloud along the coastline in an otherwise clear summer sky.

If there is already an onshore wind blowing, its strength will be increased by the sea breeze whereas if the gradient wind is onshore, the effect of the sea breeze will be to reduce or even cancel it.

On days that have experienced sea breezes the opposite effect is felt during the evening. The land and the air cool much faster than the sea and so the land breeze becomes established.

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Click on the image above to view regional internet weather


Sources & Type of Information
H.F. & VHF Radio

Shipping Forecasts on BBC Radio 4 (200 kHz and 15OOm) are the main source of weather information for the sea areas between South Iceland and Cape Finisterre. They are broadcast every six hours and include gale warnings in operation, a general synopsis, and forecasts for the different sea areas and reports of actual weather from selected stations.

In the South East Asian Regions
Bangkok Meteorology Service broadcast a regional weather forecast hourly in English and Thai on 6765.1 kHz.
Singapore Radio also broadcast a regional weather forecast on their calling channels 804, 821 and 1219 throughout the day and can be telephoned in Singapore on 4813668 during business hours for further Information.
If you are heading for Indonesia and Micronesia, Darwin Radio VID have daily High Seas Forecasts covering these regions on all their working frequencies

A little practice and some form of shorthand are needed to write down all the relevant information in the time available. Weather forecast maps and forms are useful aids. Shipping forecasts provide good background information for the sailor, but the information is often not very specific.

Inshore Waters Forecasts on Radio 3 (medium wave and VHF) are broadcast less frequently but serve to build up the general picture of coastal conditions. Once again, the forecasts cover huge areas at a time.

Land area forecasts do not give any detailed information on wind strength or direction but give a useful indication of general weather trends.

Local Radio Stations
Most local radio stations provide weather forecasts, which is useful for sailors, since they are local. Many of the stations located in popular sailing areas have special forecasts for sailors and windsurfers.

TV Forecasts
Met satellite pictures and computer graphics have made TV forecasts one of the clearest forms of general weather information. They cannot give local detail but provide an invaluable picture of the overall weather pattern.

Telephone Forecasts
Marinecall offers dedicated recorded message forecasts for yachtsmen at premium rates, with a complete regional framework of service.

Local Press
Newspaper forecasts are inevitably out of date, when compared with many of the other sources of information. Whilst they give a general background to the weather pattern they should not be relied on by sailors as a sole source.

Coastguards and Harbor Masters
The local Coastguard station (if appropriate) and the Harbor Master's office are useful sources of information and often have local updates from other nearby sources.

Gale Warnings
These are broadcast if a gale is expected somewhere in the sea area and do not necessarily apply to the whole of that area. Of more use to the sailor is the Strong Wind Warnings broadcast on local radio when winds at Force 6 or above are expected.

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Main characteristics of High and Low Pressure areas.

A movement of air causes gradient wind from regions of high pressure to regions of low pressure. Britain's weather pattern tends to be very changeable as they are largely influenced by areas of low pressure coming in from the Atlantic, bringing with them strong winds.

In the summer, this pattern is interrupted by the appearance of anticyclones or large areas of high pressure, which bring warmer settled weather and lighter winds.

Depressions are areas of low pressure with air circulating in an anti-clockwise direction rather like a whirlpool. On weather maps they appear as swirls of isobars (the lines joining places of equal pressure). The closer the isobars to each other, the stronger the wind. Low-pressure systems tend to bring with them wind, cloud and rain.

High-pressure systems or anticyclones bring with them light, variable winds and warm weather. The air moves clockwise around the system and in an outward direction. High-pressure systems have no definite path of travel and may linger for several dAY at a time before being pushed out of the way by depressions.


Significance of major changes in Barometric Pressure

We have already seen that anticyclones are large areas with little change in pressure which result in good, settled weather. We have also seen that the closer the isobars on a synoptic chart, the stronger the wind. These are just two practical examples of the relationship between changes in barometric pressure and wind strength. The principal reason for keeping a barometer at a sailing club or yachting center is so that a clear indication of the rate of change of barometric pressure may be available. Rapidly falling or rapidly rising pressure provides a sure guide to a change in weather conditions brought by the strong winds.

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Beaufort Wind Scale

Designed as a means of grouping associated sets of wind strengths and sea states, the Beaufort scale serves as a form of code or "shorthand" for all who go to sea. Thus if a forecast indicates a Force 4, you can have a good idea not only of the wind speed to expect, but also the sea state which will be generated in open water. You will also have an idea of what sort of sailing you can expect, according to your ability.

Beaufort
Force

General
Description

Sea Criterion

Land Criterion

Windspeed in knots

0 Calm
Sea like a mirror
Calm; smoke rises vertically
 Below 1
1 Light air Ripples with appearance of scales are formed but without foam crests Wind direction shown by smoke drift but not by wind vanes 1 to 3
2 Light breeze Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break Wind felt on face, leaves rustle: ordinary vane moved by wind 4 to 6
3 Gentle breeze Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses Leaves and small twigs in constant motion. Wind extends light flags 7 to 10
4 Moderate breeze Small waves becoming longer, fairly frequent white horses Raises dust and loose paper: small branches are moved 11 to 16
5 Fresh breeze Moderate waves, taking more pronounced long form; many white horses are formed. Chance of some spray Small trees in leaf begin to sway. Crested wavelets form on inland waters 17 to 21
6 Strong breeze Large waves begin to form, white foam crests are more extensive everywhere Probably some spray Large branches in motion: whistling heard in telephone wires, umbrellas used with difficulty 22 to 27
7 Near gale Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. Whole trees in motion; inconvenience felt when walking against wind 28 to 33
8 Gale Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind Breaks twigs off trees; generally impedes progress 34 to 40
9 Severe gale High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility Slight structural damage occurs (chimney pots and slates removed) 41 to 47
10 Storm Very high waves with long overhanging crest. Resulting foam in great patches is blown in dense streaks along the direction of the wind. Whole surface takes on a white appearance. Tumbling of sea becomes heavy and shock-like Visibility affected Seldom experienced inland; trees uprooted; considerable structural damage occurs 48 to 55

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