When voyaging, or living aboard, the weather is much more a part of daily life than it is on land. In Cambridge, we would look out of the window and decide whether to take an umbrella or sunglasses. Maybe we'd check the forecast to see if Thursday's a good day to go to the park.
Now, a shift in the wind can make the difference between a comfortable night at anchor or sleepless hours worrying about being blown onto the beach. On passage, knowing what's coming makes a dramatic difference to the length and comfort of the trip.
We have various ways of knowing what's coming:
- the sky and the sea : Despite having huge amounts of information available electronically, sometimes the best forecast for the next few hours comes from how things look and feel. Big black clouds to windward, an ocean swell ona calm day, a sudden change in the wind, all can suggest a change on the way.
- the barometer : One of the oldest forecasting tools, the barometer measures the pressure, or weight of the air above us. Since changes in pressure relate closely to weather, we monitor how fast or slowly the barometer is moving. A rapid fall is bad news.
- The radio: We can get the shipping forecast on BBC Radio 4, of course. In the UK, we get inshore forecasts from the coastguard on the VHF radio four times a day. Offshore, we can get weather information on our long range radio (the SSB, or Single Side Band set), and there's an amazing Canadian chap, Herb, who, as his hobby, provides weather routing advice for yachts crossing the Atlantic.
- The internet: Only available to us on shore, but full of weather info. In the UK, the MetOffice is our main source. We use the land forecasts, the inshore waters, and the shipping forecast.
- 'GRIB' files by EMAIL: We can get small files over our radio email link and there is a service called 'saildocs' which automatically emails us weather information each day. The most useful of these are called 'grib' files, which divide the world into small squares and predict the wind, pressure and rainfall in each square for the next 7 days. This is done by some powerful computer models in the US and UK, and the results are publically available. Saildocs looks at these, extracts the data for the bit of the world you are interested in and sends it to us. We can then interpret these with a little graphical software program - we use GRIB-US which will manage the data and produce an animated picture over the coming week.
- NAVTEX: All across the world, there is a network of radio stations transmitting weather forecasts at various times. We have a small black box that receives these signals, decodes them and stores the forecasts. This means that we can get a forecast up to about 200 miles offshore.
- Weatherfax: Our SSB (long range radio) can pick up weatherfax transmisions, which are sent continuously on certain frequencies. The computer can decode these and show us the resulting fax, which gives the pressure charts that we can interpret and make our own forecast.