Module 13 - Meteorology
Weather and the Sailor
What you will learn
Build a weather evidence loop for a coastal passage: obtain current official information, relate it to the route and crew, set change-of-plan triggers, and keep monitoring.
A forecast is decision evidence, not a promise. The skipper combines its issue time, validity, coverage and warnings with the route, tide, vessel, crew and conditions actually observed.
Weather affects more than sail choice. Wind direction can turn a coast into a lee shore, wind against tide can steepen the sea, poor visibility can increase the navigation workload, and cold, rain or motion can reduce crew capability. The useful question is therefore not simply ‘what is the weather?’ but ‘what does this evidence mean for this route, boat and crew at this time?’
Before departure, obtain the relevant current marine forecast and warnings. Record the issue time, valid period and geographical area before translating wind, sea state, weather and visibility into the exposed legs, tidal gates, harbour entrances and alternatives on the plan. The MCA also advises checking the forecast and obtaining regular updates when out for any length of time.
During the passage, compare the forecast with the barometer, cloud, visibility, wind and sea state actually observed. Decide in advance what would trigger an earlier reef, a shorter route, a different harbour, delay or return. That turns monitoring into an action loop instead of passive weather watching.
| Evidence | Question to answer | Decision it can change |
|---|---|---|
| Issue and validity | Is this information current for the passage time? | Depart, delay or obtain a newer issue |
| Wind and sea state | Where will direction, tide, fetch and exposure make conditions harder? | Route, timing, sail plan and sea-room margin |
| Weather and visibility | Which legs or approaches gain navigation and crew workload? | Pilotage method, watchkeeping and alternative harbour |
| Warnings | Does an official warning affect the route or period? | Reassess the passage rather than treating the base forecast alone |
| Observed trend | Are pressure, cloud, wind, visibility and sea matching the expected sequence? | Continue, shorten, divert or return while options remain |
Turn a forecast into passage decisions
The inshore forecast gives southwesterly 4 or 5, increasing 6 later, with rain and moderate visibility. The final leg is exposed to the southwest and the destination has a narrow entrance.
1. Check the evidence
Confirm the forecast area, issue time, valid period, warnings and what ‘later’ means in that product.
2. Map the exposure
Mark when the route becomes exposed, how wind and tide may combine there, and which harbour approaches become harder.
3. Set triggers
Choose observable limits for departure, shortening the route, using an alternative or turning back before options narrow.
4. Monitor
Compare updates and observations with the expected sequence, then act while the safer alternative remains available.
Sense check: A forecast that remains technically inside a vessel’s limits may still be unsuitable for this crew, tide, route or harbour entrance.
Common mistake or limitation
- Using a screenshot or app icon without checking when the forecast was issued, what period it covers or whether warnings have changed.
- Choosing the most favourable model output rather than the authoritative marine information relevant to the route.
- Checking once before departure but setting no observable trigger for shortening, diverting or stopping the passage.
Recap
- Start with current marine information, its warnings, issue time, validity and coverage.
- Translate weather into route, tide, vessel, crew and harbour consequences.
- Keep comparing forecast and observations, using pre-decided change-of-plan triggers.
Optional quick check
Section 1 of 6
Which pre-departure note is most useful for a coastal passage?
Sources and factual review
Continue studying Meteorology
This public lesson is part of Revision Module 13. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.