Module 13 - Meteorology
Weather and the Sailor
What you will learn
Build a weather evidence loop for an exposed coastal passage: obtain current information, map it to the route, set decision triggers and keep checking reality.
A forecast is time-bounded evidence, not a promise. Coastal-level judgement connects official information and observed change to the route, tide, vessel, crew and available refuges.
Weather changes the risk of the whole passage. Wind direction can create a lee shore, wind against tide can steepen the sea, rain or fog can raise pilotage workload, and cold, motion or delay can reduce crew capability. The useful question is therefore not only what weather is forecast, but what that evidence means at each exposed leg and harbour approach.
Before departure, record the relevant warnings, issue time, valid period and area. Translate the forecast wind, sea state, weather and visibility into route consequences, then identify an earlier reefing point, shorter route, alternative harbour or no-go trigger. The MCA advises checking weather before departure and obtaining regular updates when out for any length of time.
During the passage, compare updates with pressure tendency, cloud, visibility, wind and sea actually observed. A mismatch is information: it may mean a system is early, late, stronger, weaker or locally modified. Act while the safer option still has sea room and daylight rather than waiting for certainty.
| Evidence | Coastal-level question | Decision it can change |
|---|---|---|
| Issue and validity | Is this current for the route time? | Depart, delay or obtain a newer issue |
| Wind and sea | Where do direction, tide, fetch and exposure combine? | Timing, sail plan, route and sea-room margin |
| Visibility and weather | Which leg or entrance gains workload? | Pilotage method, watchkeeping and refuge |
| Observed trend | Is reality following the expected sequence? | Continue, shorten, divert or return |
Turn a forecast into a route decision
The inshore forecast gives southwest 4 or 5, increasing 6 soon, rain and moderate visibility. The destination entrance is exposed to the southwest and the ebb will oppose the wind.
1. Anchor the evidence
Confirm the forecast area, warnings, issue time and the exact period covered by ‘soon’.
2. Map the exposure
Mark when the route reaches the headland, opposing stream and exposed entrance.
3. Set triggers
Choose observable limits for reefing, using a nearer harbour, delaying or turning back.
4. Keep checking
Compare updates and observations with the expected sequence, then act before the fallback closes.
Sense check: A forecast inside the yacht’s nominal limits may still be unsuitable for this crew, tide, route or harbour entrance.
Common mistake or limitation
- Using a weather-app symbol or model number without checking its issue time, validity, warnings or marine coverage.
- Treating a forecast as a guarantee instead of comparing it with current observations and later issues.
- Waiting for a limit to be exceeded before deciding where to shorten, divert or stop.
Recap
- Use current official information with its warnings, issue time, validity and coverage.
- Translate weather into consequences for the actual route, vessel and crew.
- Monitor against pre-decided triggers and preserve an alternative.
Optional quick check
Section 1 of 15
Which passage note is most useful before departure?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Meteorology
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