Coastal sailing combines regional weather with highly local effects. A forecast for the departure harbour may not describe a headland, tidal race or the entrance you reach hours later. Build the weather plan around where the boat will be, not where it starts.
Divide the passage into decision segments
Mark departure, exposed headlands, narrows, potential bars or shallow approaches, diversion ports and arrival. For each segment, estimate a time range using realistic boat speed. Read every official forecast zone crossed and include the next zone if a diversion might take you there.
Add tides and current to the weather
Consult current local tide tables and tidal-stream information from the relevant hydrographic or port authority. Wind opposing a strong tidal stream can steepen waves, especially in constricted water or near a headland. A favourable tide at the start may reverse before you reach the difficult point. Do not treat a tide prediction as a weather forecast or an offshore wave grid as a harbour-entry forecast.
Check the arrival before departure
Look at the entrance’s forecast wind direction, swell exposure, visibility, daylight and tide around the likely arrival window, including a delayed arrival. Confirm local restrictions, pilotage information and an alternative you can reach without depending on the same weather window.
Set gates you can still act on
Before an exposed section, compare actual wind and sea with the newest bulletin and observations. Decide in advance what change means returning, diverting or waiting. A refuge that is safe in one wind direction may not be suitable if it shifts; assess access conditions as well as distance.
Departure card
- Official zones and warnings for the full route.
- Estimated time at the headland, narrows and destination.
- Wind, sea, visibility and tide/current at those times.
- Latest safe diversion point, alternative port and next forecast update.
Official sources
- UK Met Office: Guide to marine forecasts
- UK Maritime and Coastguard Agency: Weather and tide information
- NOAA/NWS: Marine forecast zones
Important: This is practical passage guidance, not a forecast for your specific departure or a navigational route. Personalised forecasts with AI and experts are in closed testing. Before and during a passage, check the latest official forecasts and warnings for your area; the skipper decides in light of actual conditions, vessel and crew.
Keep height of tide and tidal stream separate
For each critical approach, keep two records: water level relative to the chart datum, and the stream direction/speed for that place and time. High water at a reference port is not a universal slack-water time. A tide curve must not be repurposed as a current forecast. Local approach instructions and restrictions are a third, separate source.
Test the alternative against the same hazard
A nearby diversion may face the same swell or require passing the same headland. Compare its entrance orientation, ETA range and current restrictions before describing it as a refuge. Mark the last point from which it remains achievable; route length alone does not establish a usable alternative.
- RYA: passage planning — Passage preparation and route, vessel and crew context.
Editorial review of this material: 27 September 2026. This date concerns the page content; check current forecast issue times and validity at the original sources.