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Conditions and forecasts

Marine weather: forecasts, observations and decisions

Review the Beaufort scale

The essentials

Marine weather planning combines an appropriate forecast with recent observations and a conservative decision. Pressure tendency, wind direction and strength, cloud, visibility, sea state and fronts provide related evidence; no single sign proves what will happen. The plan should state limits, alternatives and a time to reassess as the forecast and actual conditions evolve.

By · Reviewed 2026-09-08 · independent learning guidance

Scope: The source examples are UK marine forecasts. Use the current official marine forecast and warnings for the waters you are actually sailing, then set limits for the boat and crew.

Which forecast information matters to a small craft?

Use an official marine forecast for the relevant area and period, then note wind, sea state, weather, visibility and warnings. Check issue and validity times so yesterday's forecast is not mistaken for current guidance. Local effects around headlands, valleys, coasts and strong tides may make conditions differ from a broad-area summary.

What does pressure tendency tell you?

A barometer trend can support the wider weather picture, especially when the rate of change is considered, but pressure alone does not specify the wind or prove a particular front. Compare the observed tendency with the forecast, sky, wind and timing. Unexpected divergence is a reason to update the plan rather than explain it away.

How does weather become a go-or-no-go decision?

Translate the forecast into effects on this boat and crew: wind against tide, shelter, visibility, temperature, daylight, sea room and the difficulty of the destination. Set limits before departure, identify an easier alternative, and preserve enough time and fuel to change the plan.

  • Check source, issue time, validity and area.
  • Compare forecast with observations throughout the passage.
  • Choose limits for the actual boat, crew and route.

Primary references used for this guide

Compass is an independent revision publisher. These maintained official, regulatory and standards-body references anchor the scope above; always check their current operational material for a real passage.

Check your understanding

Weather questions

3 selected answers

In navigation, what is 'fetch'?

The distance over water for which wind blows in a broadly consistent direction—one factor in wave development

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What is a lee shore and why is it considered dangerous?

A shore towards which the wind blows — dangerous because wind and waves can reduce sea room and drive the vessel towards danger

Read the answer

What is a weather shore?

A shore from which the wind is blowing; it may reduce local fetch to leeward but does not guarantee shelter

Read the answer