Weather on board
Where Zora's forecast comes from, how the boat keeps it for when you are offline, and what it cannot tell you. To show the weather, see Weather.
Where the forecast comes from
The forecast on the chart is NOAA's GFS unless you choose another model on the layer's chip (see Change how a layer is drawn). GFS is a global weather model. Its values sit on a grid a quarter of a degree apart, about 15 nautical miles north to south. It runs four times a day, at 00, 06, 12 and 18 UTC, and each run looks 120 hours ahead. The waves come from GFS's own wave model. A layer's settings name the model it is drawn from.
A value on the chart is the model's figure for its whole grid cell.
The Weather screen is a different forecast: Windy's, fetched live from the internet each time you open it.
How the boat keeps it
Every screen reads the forecast from the boat, which keeps what it has fetched on its own storage.
With Keep the forecast current on, the boat looks for the newest forecast every 15 minutes, and 30 seconds after Zora starts. It downloads the parameters you chose, over the period you chose, the nearest hours first and across all of them at once. A download cut short when the connection drops still leaves you the next hours of everything. Hours already past are skipped.
So download while you have a connection, in the marina or near the coast, and the forecast goes offshore with you.
A parameter you did not choose is downloaded only when you look at it, and only while there is a connection.
The boat stops downloading when its storage has less than 1 GB free, to keep room for everything else Zora stores.
Tidal current
Zora works out the tidal current on the boat from a tidal atlas, for any hour you ask, with no internet. Set is the direction the water flows toward, in degrees true.
The atlas stops short of the coast. Close inshore there is no value to show.
Your barometer
When the boat has a barometer, Zora watches how the pressure moves over the last hour and the last three hours, and tells you with a notification: Weather Pressure falling, Weather Pressure falling quickly or Weather Pressure falling rapidly, and the same for rising. Falling quickly comes as an alert, falling rapidly as a warning. Zora works this out on the boat, with no internet. It needs an hour of readings first, so the first notification comes an hour after the barometer starts reporting.