1. Start with warnings

Look first for current official warnings and advisories from the responsible national meteorological service. Check the area, start time, duration and the exact hazard. If you have to cross more than one forecast zone, read each one. An attractive forecast for your departure marina does not describe the exposed leg offshore.

2. Read the time and the trend

Forecasts are time-dependent. Note the issue time, the valid period and the units before comparing sources. Ask whether wind or sea state is building or easing during your expected passage, not merely what is forecast at departure. An older forecast may be superseded by a later warning.

3. Look beyond average wind

Check gusts, wind direction, wave height and direction, swell, visibility and any local effects. The same wind can be much harder when it opposes waves or current, or when the route offers little shelter. Compare the conditions with the vessel, crew, daylight and available alternatives.

4. Compare with observations

Recent observations from buoys, coastal stations and nearby vessels can show whether the current situation resembles the forecast. One observation does not invalidate a regional forecast, but a meaningful mismatch is a reason to inspect the latest update and use extra caution.

5. Make the decision reversible

Write down a departure threshold, a later update time, a diversion and a clear reason to postpone. Do not let a favourable number in one app replace the official warning picture or your own seamanship.

Primary sources: NOAA/NWS Marine Weather Services and the Met Office guide to marine forecasts. These explain products and terminology; always open the live forecast for your actual area.

Wind direction changes the passage

Direction matters as much as strength. A beam reach, a long upwind leg and a following sea can feel very different under the same forecast wind. Consider how the direction will change along the route and over time, and where you could seek shelter.

Wave height needs context

Wave height alone does not describe the sea. Check wave period and direction, the mix of wind waves and swell, and whether waves are likely to steepen in shallow water or against a current. A forecast can also smooth out short-lived local effects. Compare the forecast with recent buoy observations when available.

Build a margin

Before departure, assess conditions against your particular vessel and crew. Include a margin for gusts, uncertainty, fatigue, darkness and the distance to shelter. A fixed universal “go/no-go” wind speed would hide these differences.

Primary sources: NOAA/NWS Marine Weather Services links to forecasts, observations and warnings; the Met Office marine guide explains terms used in coastal forecasts. Use their latest local products for operational decisions.

Check that you are comparing like with like

Match location, time zone, forecast hour, units and the exact variable. A forecast issued six hours later is not simply another vote on the same conditions. A point forecast and an official zone forecast also answer different questions.

Start with the authoritative warning picture

Review official warnings and marine forecasts for the route first. Model graphics can add detail, but they do not cancel a warning. Check whether the disagreement is about a small numerical difference or a change that would affect safe departure, a critical waypoint or your return options.

Reduce exposure to the uncertain part

If the forecast spread covers the time you would be farthest from shelter, a later departure, shorter leg or more conservative route may be more robust. Record what would make you reassess: an updated warning, a shift in observations, or a new forecast run.

Keep the forecast live

A passage plan needs a scheduled refresh. If you will be offshore or have limited connectivity, identify in advance how you will obtain the next forecast and warnings. NOAA/NWS, for example, publishes marine text products designed for low-bandwidth use in its covered areas.

Primary source: NOAA/NWS Marine Weather Services lists official coastal, offshore, high-seas, observation and low-bandwidth text products. This article is a decision framework, not a live forecast.