Module 13 - Meteorology

Yachtmaster Offshore Standard: Weather Evidence and Action

What you will learn

Run a weather decision cycle that connects current forecast evidence and observed change to route exposure, crew capability, an early action trigger and a usable fallback.

Yachtmaster meteorology is not pattern naming alone. The skipper must time-stamp the evidence, test whether reality follows the expected sequence and change the passage while safer options remain controllable.

The RYA theory scope includes taking and interpreting forecasts, plotting weather systems and making weather predictions with a barometer; the practical examination may assess meteorology as part of skippering. Written revision can rehearse the evidence and decision structure, but it cannot demonstrate live observation, vessel handling, crew leadership or command competence.

Start with an evidence ledger: source, warning status, issue time, valid period, forecast area, expected sequence and limits. Add observations at stated times — calibrated pressure, wind, cloud, visibility, temperature and sea state — and distinguish a measured fact from an interpretation. An app icon or remembered phrase without its issue and validity is not a defensible forecast record.

Compare expected and observed sequences. A front, trough or local effect may be consistent with several cues, but one pressure change, cloud type or wind shift does not prove the diagnosis. Pressure tendency and wind timing do not by themselves prove which system is present. When sources or observations disagree, name the conflict and act for the safer credible case while obtaining a fresh official forecast or warning.

Translate the weather into passage consequences: lee shore, wind against tide, harbour exposure, pilotage workload, speed loss, daylight, crew fatigue and refuge access. Set triggers before the exposed leg, such as a pressure tendency, wind or sea state, visibility, crew state, latest diversion time or minimum arrival margin. The trigger exists to create action, not merely another note in the log.

Close the loop with a short brief: facts, uncertainty, action now, roles, fallback and the exact evidence that can reopen the original route. The MCA advises checking the weather before departure, obtaining regular updates on longer trips and considering refuge if conditions deteriorate. All values below are fictional revision data; use current official and local information and the vessel's procedures for a real passage.

Worked example

A fictional 0500 forecast says southwest 4 or 5, increasing 6 later. The yacht records 1012.4 hPa at 0900 and 1007.1 hPa at 1200; by 1200 the observed wind is already Force 6 with a building sea.

1Pressure change: 1012.4 − 1007.1 = 5.3 hPa in the preceding three hours.
2The Met Office station-report band for 3.6–6.0 hPa in three hours is falling quickly. It is not the more-than-6.0 hPa very-rapid band.
3‘Later’ means more than twelve hours from the 0500 issue, so the forecast wording places the increase after 1700 within the forecast period. Force 6 observed by 1200 is a material mismatch with that timing.
4The pressure tendency and early wind increase are two cues, but they do not by themselves prove which front or feature is present. Cross-check a current forecast, warnings, synoptic chart, cloud, visibility, temperature and sea state.
5Protect the route and fallback for the stronger or earlier credible case now; do not wait for a perfect diagnosis before reducing exposure.

Sense check: The arithmetic classifies the measured tendency. It does not turn the barometer into a complete forecast or prove that the original route remains safe.

Yachtmaster Offshore Standard: Weather Evidence and Action
Decision field	Evidence to record	Command question
Forecast status	Warnings, source, issue, validity, area and defined timing words	Is this current for the route and time?
Observed change	Timed pressure, wind, cloud, visibility, temperature and sea state	Is reality following the expected sequence?
Passage consequence	Exposure, tide, speed, daylight, crew and refuge margin	Which safe option becomes harder next?
Trigger and fallback	Observable limit, latest decision time, action and owner	What happens now, and what evidence can reopen the plan?

Run a closed-loop weather brief

The watch reports an earlier wind increase and the crew ask whether the passage can continue to the exposed entrance.

1. Anchor
State the current warning, forecast source, issue and validity, route area and observation times.
2. Compare
Name what matches, what conflicts and which parts are measured facts, interpretation or unresolved assumptions.
3. Apply
Convert the credible weather cases into sea state, speed, tide, visibility, crew and harbour consequences.
4. Act and reopen
Give the helm and crew an action, fallback and monitoring roles, plus the exact evidence and margin required before reconsidering the route.

Sense check: If the brief cannot say when the original route closes and what can reopen it, the weather information has not yet become a command decision.

Common mistake or limitation

Treating a pressure fall, cloud sequence or wind shift as proof of one weather system rather than evidence to cross-check.
Quoting the latest forecast without its issue time, validity, warning status or relevance to the route time.
Waiting for the forecast limit to arrive before choosing where to reef, shorten, hold, divert or return.
Giving the crew a technical diagnosis without an action, roles, fallback and reopening trigger.

Recap

Time-stamp forecast and observation evidence before interpreting it.
Use several independent cues and name conflicts; one cue does not prove a system.
Translate weather into route, tide, crew and refuge consequences.
Act at a pre-decided trigger and brief the condition that can reopen the route.

Optional quick check

Section 14 of 15

The pressure falls 5.3 hPa in three hours and Force 6 arrives earlier than the forecast timing. What is the strongest Yachtmaster response?

Sources and factual review

Reviewed 20 August 2026 - Compass Revision editorial 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.

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