Methodology

How theviz turns weather history into a visibility forecast

Calm water today does not mean clear water today.

1. Offshore swell and weather

The forecast on theviz reads multiple global wave and atmospheric models. It uses significant wave height, period and direction, as well as wind and rainfall-related context, rather than relying on a single source or a single headline swell figure.

2. Site-specific exposure

Each named site has an exposure geometry. The model estimates how much offshore wave energy reaches that location, accounting for direction, shelter and the greater ability of long-period swell to wrap around headlands.

3. Bottom stirring and settling

Waves that reach the seabed can mobilise sediment. To follow that, theviz estimates near-bottom wave motion, accumulates recent stirring, and lets the suspended load decay over a site-specific settling period. This gives the forecast memory.

4. An ensemble, not a single number

Each weather-model combination is run separately, and theviz then reports a median, a 10th–90th percentile range and threshold probabilities. A wide range means the weather models disagree.

5. Separate clarity from safety

Visibility is not a safety score. Entry/exit, surge, wind, surface chop and current are evaluated separately; a good clarity estimate never overrides a limiting condition.

Limitations

Not every local process is modelled directly by theviz, including site-scale currents, stormwater plumes, plankton blooms, thermoclines or detailed bathymetry. It is an aid to judgment, not a substitute for local observation, formal forecasts, marine notices or personal experience.