Module 13 - Meteorology
Shipping Forecast Terminology
What you will learn
Decode a UK Shipping Forecast phrase into wind, timing, weather, visibility and sea-state implications, using the stated issue and validity times.
Shipping Forecast words have defined meanings. Decode them in order and relate timing terms to the forecast issue time, not to when you happen to hear or read the bulletin.
The Met Office issues the Shipping Forecast four times daily for 31 sea areas around and approaching the British Isles. Each issue gives any gale warnings, a general synopsis and area forecasts. Read the printed issue time and valid period before interpreting the compressed wording; a recording or cached page can otherwise sound current when it is not.
Wind direction names where the wind comes from. Veering is a clockwise change, such as southwest to west; backing is anticlockwise. Force numbers describe the forecast wind range. ‘Imminent’ means within six hours of issue, ‘soon’ means six to 12 hours from issue, and ‘later’ means more than 12 hours from issue within the forecast period.
The visibility categories are very poor below 1,000 metres, poor from 1,000 metres to 2 nautical miles, moderate from 2 to 5 nautical miles, and good above 5 nautical miles. ‘Fog’ may appear as a weather description, but the official visibility category below 1,000 metres is ‘very poor’. Sea-state words also have ranges: smooth is below 0.5 m, moderate is 1.25–2.5 m and rough is 2.5–4 m.
Worked example
A 0500 UTC forecast says the wind will increase Force 6 ‘soon’, and the exposed leg is planned for 1400 UTC.
- 1Calculate the ‘soon’ window from the issue: 0500 + 6 hours = 1100; 0500 + 12 hours = 1700.
- 2The planned 1400 leg sits inside that 1100–1700 window, so plan for the increase rather than the starting force.
- 3Check the actual valid period, later updates, warnings, local effects and observations before deciding whether to depart or alter the plan.
Sense check: The arithmetic is based on the forecast issue time. Hearing it later does not move the forecast event window.
| Term | Defined meaning | Decision cue |
|---|---|---|
| Veering / backing | Clockwise / anticlockwise wind-direction change | Work out the new exposure and point of sail |
| Imminent | Within 6 hours of issue | May affect the early passage |
| Soon | 6–12 hours after issue | Compare with the route timetable |
| Later | More than 12 hours after issue | Check whether the vessel will still be exposed |
| Very poor | Visibility below 1,000 m | Plan for restricted visibility and greater navigation workload |
| Poor / moderate / good | 1,000 m–2 M / 2–5 M / above 5 M | Relate the range to lookout, pilotage and traffic |
| Smooth / moderate / rough sea | Below 0.5 m / 1.25–2.5 m / 2.5–4 m | Apply vessel, tide, fetch and route context |
Decode one area forecast before applying it
At 0500 UTC an issue says: ‘Southwest 4 or 5, increasing 6 soon, veering west later. Moderate. Rain then showers. Moderate or good, occasionally poor.’
1. Anchor the clock
‘Soon’ is six to 12 hours after the 0500 issue: approximately 1100–1700 UTC. ‘Later’ begins more than 12 hours after issue.
2. Decode wind
The wind comes from the southwest, increases to Force 6, then changes clockwise towards west.
3. Decode conditions
Moderate sea state means 1.25–2.5 m; rain gives way to showers; visibility may occasionally fall into the poor band.
4. Apply
Compare that sequence with the passage timetable, local effects, tide, lee shores, harbour approaches and alternatives.
Sense check: If the forecast was heard at 0900 from a recording, ‘soon’ still runs from the 0500 issue time, not from 0900.
Common mistake or limitation
- Reading a westerly as wind travelling west; forecast direction is the direction from which it blows.
- Starting ‘soon’ or ‘later’ from the time the forecast was heard rather than the printed issue time.
- Calling visibility below 1,000 metres ‘fog’ as the category; the marine visibility category is ‘very poor’, while fog is weather.
Recap
- Forecast wind direction is where the wind comes from; veering is clockwise and backing anticlockwise.
- Imminent, soon and later are timed from issue: within 6 hours, 6–12 hours and more than 12 hours.
- Below 1,000 metres is ‘very poor’ visibility; sea-state words have separate wave-height ranges.
Optional quick check
Section 3 of 6
A forecast issued at 0500 UTC says conditions will change ‘soon’. Which window does that mean?
Sources and factual review
Reviewed 19 August 2026 - Day Skipper Revision.
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