Two forecast displays can disagree because they use different models, update times, spatial resolutions or interpretations of the same data. The disagreement is useful information: it tells you to look more closely, especially when a departure decision depends on a narrow weather window.
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.