A forecast is not a measurement

Nobody has measured tomorrow. Weather forecasts come from computer models that estimate what the atmosphere will do next. Different models often produce different answers, especially several days out.

When sources disagree, we use the one that has performed best in our testing for these waters. Rather than averaging forecasts together, we show the source we trust most for that specific piece of information.

Tides are different

Tides are not forecasts in the usual sense. They are based on the predictable movement of the moon and sun, refined by decades of measurements at local gauges.

A tide table for next August is nearly as dependable as one for tomorrow. It is the most reliable data in the app, which is why we take it directly from the agencies that maintain the gauges.

What each source supplies

• Wind, gusts, temperature, visibility, and daylight — Open-Meteo. In our testing against real buoy observations, it was the most accurate source we evaluated and consistently provides gust forecasts, which not every provider does.
• Chance of rain — National Weather Service. We switched after comparing multiple sources at several harbors. For boating decisions, understating the chance of rain is generally more problematic than overstating it.
• Tides — NOAA CO-OPS, the same network that supports published U.S. tide tables. For waters outside NOAA coverage, we use WorldTides.
• Waves, swell, and water temperature — Open-Meteo Marine. Waves here are modelled rather than measured: the buoys that report wave height sit well offshore, not in the Sound. Where the model has no water temperature, we use the nearest NOAA gauge.
• Warnings and advisories — National Weather Service. Marine advisories come directly from the marine forecast zone that covers your harbor. A Small Craft Advisory is a marine product and may not appear in land-based forecasts.
• Weather icons — OpenWeather. Also serves as a backup weather source if Open-Meteo is unavailable.
• Place names and coordinates — Nominatim, built on OpenStreetMap data.

How fresh the data is

The line under the harbor name, such as “Conditions as of 3:58 PM,” shows when the observation was reported by the weather service, not when the page was loaded.

If the data is from a previous day, Aweigh makes that clear. A forecast that has quietly gone stale is worse than one that admits its age.

What this does not do

Aweigh compares the forecast against limits you choose.

It does not know your boat, your crew, your experience level, or what the water looks like out the window. The decision to go is yours, and the conditions you see on the day always matter more than anything on a screen.