Module 13 - Meteorology
Barometer trends: evidence for a Yachtmaster passage decision
A barometer or barograph supplies one important strand of short-range weather evidence. A pressure trend must be read with the current marine forecast, wind, cloud, visibility, sea state, the vessel's position relative to weather systems, and the instrument's calibration; a rising or falling value is not a complete forecast on its own.
The Met Office classifies three-hour pressure tendency in station reports: 0.1–1.5 hPa is rising or falling slowly, 1.6–3.5 hPa is rising or falling, 3.6–6.0 hPa is rising or falling quickly, and more than 6.0 hPa is rising or falling very rapidly. These labels describe the measured tendency; they do not by themselves prove a particular front, storm strength, or safe operating limit.
Log pressure at a consistent interval suited to the passage and compare the change with successive forecasts and observations. A Yachtmaster decision states what trend would prompt an earlier reef, route change, shelter, delay, or fresh forecast check, while preserving a contingency if the expected weather sequence does not appear.
- Treat the pressure trend as evidence to combine with forecasts and observations
- 0.1–1.5 hPa in 3 hours = rising or falling slowly
- 3.6–6.0 hPa in 3 hours = rising or falling quickly
- More than 6.0 hPa in 3 hours = rising or falling very rapidly
- Use a consistent risk-based logging interval and pre-agreed action triggers
- Standard pressure = 1013 mb (hPa)
Watch for this: A change in tendency may be consistent with a frontal passage, but confirm it against the forecast, wind, cloud, temperature, visibility and sea state before changing the plan.
Sources and factual review
Reviewed 12 August 2026 - Compass Revision editorial review.
Apply meteorology to a skipper decision
The full module connects pressure, forecasts, fronts, observations and local effects to passage limits and contingencies.