Passages and their planning consist of the three Ds: departure, duration and destination, but they must include the factors mentioned under voyage planning: understanding currents, and a long-term overview of wind trends. It’s important to bear in mind the general wind trend if the passage is five days or over, because though the specific forecast may deviate from the prevailing, or expected pattern, there will be a high probability it will revert to the norm at some point during the passage...
Wind pilots provide a pattern of wind direction, but they are a historic record of wind direction and strength. They are by no means a forecast.
In recent years I have noticed much greater variations from the wind pilot’s historic data, as global warming affects the world’s climate, a factor that therefore needs to be borne in mind.
We now need to consider weather forecast charts, to see how the weather systems impacting our passage are moving, and their strengths and directions.
Start looking at the weather charts 10-14 days before departure to get a feel of how the weather systems are developing, then plan an intended route a day or two before actual departure. As the passage progresses, check the weather charts daily and modify the route accordingly to take account of forecast changes.
It’s important to remember it is a forecast not a guarantee of weather to come. It will not show very local weather variations, such as small intense thunderstorms, so be wary especially in the tropics. A squally thunderstorm can creep up on you, suddenly increasing winds from five to 40 knots in just minutes, then be gone again 20 minutes later. If you get caught with your cruising chute up you will get it down again but perhaps in more than one piece.
As a rule of thumb, you can expect 90–95% accuracy for a forecast over the next 24 hours. This reduces to 75- 80% in the following 48 hours and to 60-65% for 72 hours; 40-50% for 96 hours and 25-30% for 120 hours.
If your passage plan takes you along a coast ensure you have a pilot guide or a large scale wind pilot to make sense of local wind patterns and variations.
Kraken Yachts’ partner in offshore communications, Ed Wildgoose, Mailasail’s managing director talked to me about the satellite, phone systems and weather forecast suppliers that are available to keep the bluewater cruiser informed anywhere in the world. Communication options, GRIB file providers and GRIB file viewers is a complex subject that merits an article in its own right. Still, I cannot stress enough the benefits of satellite communication especially for up-to-date weather forecasting and cyclone tracking. I consider sat comm connection as safety equipment second only to a life-raft, and a very close second at that.
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