A weather app’s headline wind number is useful only when you know what it represents. It may be an average over a period, while short gusts can be materially stronger. The number may describe one grid point rather than a narrow channel, headland or the full passage.
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.