GRIB Files

Download, import and merge GRIB weather files over your sailing area, then replay the forecast hour by hour on the map — including offline.

Where to find it

Map › Forecast button (top of the map, with a GRIB badge once a file is loaded) › GRIB tab.

The forecast panel has two tabs: - OpenMeteo — the online API forecast (wind / pressure / waves). - GRIB — the subject of this page: load a GRIB file that takes over from the API and feeds the whole app (map, routing, AI agent).

Hierarchy

Forecast
└── GRIB tab
    ├── No GRIB loaded
    │   ├── Download section
    │   │   ├── Zone source: Route / Zone
    │   │   ├── [Route] Auto-fetch GRIB (Open-Meteo)
    │   │   ├── [Route] Download GRIB (ECMWF / GFS / AIFS)
    │   │   └── [Route] SailDocs Request
    │   │   └── [Zone] Draw zone on map → Auto-fetch GRIB
    │   ├── Import section
    │   │   ├── Import GRIB file (local file / drag-drop)
    │   │   ├── Fetch from URL (direct URL)
    │   │   ├── Watch folder (folder monitoring)
    │   │   └── + Merge a GRIB (when a GRIB is already loaded)
    │   └── Cache & budget
    │       ├── GRIB Cache (save / reload)
    │       └── Data Budget (size/time estimator)
    └── GRIB loaded
        ├── View mode: Wind / Pressure / Waves
        ├── Day selector + time-step slider (Play/Pause)
        ├── Filename + close (clear GRIB)
        ├── Merged GRIBs (source stack)
        └── Route Weather along the track

Understanding the principle

What a GRIB is for

What it's for: A GRIB is a compact weather file (wind, pressure, waves, swell, sometimes currents) on a geographic grid across several forecast steps. While a GRIB is loaded it replaces the API forecast everywhere in the app: map display, routing calculations, and the context handed to the AI agent. It is the ideal source at sea, where you download one light file once (over satellite or harbour wifi) and then sail on it offline.

How to use it: 1. Open Forecast, then the GRIB tab. 2. Pick a way to obtain a file: direct download, SailDocs e-mail request, local import, or URL. 3. Once the file loads, the GRIB badge appears and the panel switches to the GRIB view automatically. 4. To go back to the online forecast, clear the GRIB (close button next to the filename).

Tips & limits: A GRIB only covers the area and forecast steps you downloaded; outside that, the app has no data. The larger the area, resolution and duration, the heavier the file — see Data Budget to size it for your onboard link.

Choosing the area (Route / Zone)

Zone source: Route or Zone

What it's for: Define the geographic footprint of the download — either the envelope of your active route, or a rectangle you draw by hand.

How to use it: 1. At the top of the Download section, toggle between Route and Zone. 2. Route: the app automatically computes the bounding box of your waypoints, so you need at least 2 waypoints in the active route. 3. Zone: click Draw zone on map, then click-and-drag on the map to draw a rectangle. The coordinates (S–N / W–E) appear under the button.

Options & settings:

Tips & limits: In Zone mode, while no zone is drawn an amber hint is shown. The Auto-fetch GRIB button only appears once a zone is defined. Draw tightly: an oversized zone needlessly bloats the file.

Downloading a GRIB (Download section)

Auto-fetch GRIB (Open-Meteo)

What it's for: The fastest way to get a weather grid: the app pulls Open-Meteo data directly over the chosen footprint and loads it as a GRIB, with no e-mail or file to manage.

How to use it: 1. Choose Route (active route) or Zone (drawn rectangle). 2. Click Auto-fetch GRIB (Open-Meteo). 3. Wait ("Fetching weather grid…"); the file loads and the view switches to GRIB.

Options & settings: - The tooltip shows an estimate of grid points and resolution before download. - The resulting file is automatically saved to the GRIB cache (reloadable later offline).

Tips & limits: Requires an Internet connection. If the route has fewer than 2 waypoints (or no zone is drawn), the app shows "Add waypoints to your route first".

Download GRIB (ECMWF / GFS / AIFS)

What it's for: Download a GRIB from the major deterministic models via ready-made profiles: ECMWF HRES (reference for offshore routing), GFS (up to 16 days), and AIFS (ECMWF's AI model). Available in Route mode.

How to use it: 1. Expand Download GRIB. 2. Pick a Profile from the list (see table). 3. Check the estimate (model, resolution, number of files, max forecast hour, estimated size). 4. Click Download now and follow the progress bar (wind/waves). Cancel stops it at any time.

Options & settings — available profiles:

Tips & limits: ECMWF caps at 10 days; GFS extends to 16 days for long-range planning — but past D+7 the value is synoptic only (trend, not detail). The downloaded file is added to the GRIB cache.

SailDocs Request

What it's for: Generate a pre-filled SailDocs e-mail request to receive a GRIB by e-mail — the classic method at sea over a low-bandwidth satellite link. Available in Route mode.

How to use it: 1. Expand SailDocs Request. 2. Pick a preset (see table) or Custom to set model / resolution / parameters yourself. 3. Copy the request (Copy to clipboard) or open it directly (Open in email). 4. Send the e-mail to query@saildocs.com. SailDocs replies with a GRIB by e-mail that you then import via Import GRIB file.

Options & settings:

In Custom mode: - Model: GFS, ECMWF or RTOFS. - Res.: 0.25° / 0.5° / 1.0° / 2.0°. - Params: WIND, PRESS, WAVE, GUST, CUR (currents, RTOFS only).

Tips & limits: Requires at least 2 waypoints to compute the footprint. The Currents (RTOFS) preset is the free way to get ocean currents up to ~5 days. It is the only GRIB stream not downloaded inside the app: it goes through your mailbox.

Importing a GRIB (Import section)

Import GRIB file (local file)

What it's for: Load a .grb / .grib / .grib2 file already on your machine (received from SailDocs, PredictWind, zyGrib, etc.).

How to use it: 1. Click Import GRIB file and select the file. 2. The GRIB loads; the GRIB badge appears.

Tips & limits: Accepted extensions: .grb, .grib, .grib2, .grb2. If the file holds no usable data, a "No weather data found" message appears. The imported file is also saved to the cache.

Fetch from URL

What it's for: Download a GRIB from a direct URL (e.g. a NOAA/NCEP .grb2 file) without a local file.

How to use it: 1. Click Fetch from URL. 2. Paste the URL in the field, then Fetch (or press Enter). 3. A progress bar appears; × cancels the download.

Tips & limits: The URL must be valid (otherwise "Invalid URL"). Paste a direct link to the .grb2 file, not a web page.

Watch folder (folder monitoring)

What it's for: Monitor a folder on your disk and automatically import any new GRIB that appears in it — handy if a third-party tool drops files there regularly.

How to use it: 1. Click Watch folder for GRIB files and choose a folder. 2. The watched folder shows with a green dot. Each newly detected GRIB is imported ("Imported: …"). 3. Stop ends monitoring.

Tips & limits: Works only in Chrome/Edge; otherwise a message states the feature is unsupported. If folder access is lost, re-select it.

+ Merge a GRIB (source stack)

What it's for: Combine several GRIB files into a single forecast. The first file loaded stays the primary source (reference grid and time base); later files fill in missing fields — for example adding a wave or currents GRIB on top of a wind GRIB.

How to use it: 1. Load a first GRIB (it becomes the P primary source). 2. The + Merge a GRIB button appears: click it and select a second file. 3. The Merged GRIBs stack lists the sources and, for each, the fields it contributes (wind, pressure, waves, swell, currents…).

Options & settings: - P = primary source (reference grid). - S1, S2… = secondary sources. - The × at the end of a row removes that source from the stack.

Tips & limits: Ideal for layering an (atmospheric) wind file with a currents/waves file covering the same area. The stack only appears once at least two files are merged.

Cache & budget

GRIB Cache (save / reload)

What it's for: Every downloaded or imported GRIB is automatically kept on the device. The cache lets you reload a file offline without re-downloading it — essential at sea.

How to use it: 1. Expand GRIB Cache: the list of kept files appears (name, reference date, number of steps, size, parameter badges). 2. Click a row's download icon to reload that GRIB. 3. A row's trash icon deletes that file; the summary trash icon (Clear all) empties the whole cache.

Options & settings: - Per-file parameter badges: wind, press, waves, swell, and a "no wind" warning if the file lacks wind. - An expired tag on files whose reference date has passed. - Refresh: refreshes the list.

Tips & limits: An "expired" file remains reloadable, but its data is old — avoid it for a navigation decision. The cache uses disk space (total size shown); clean it up regularly.

Data Budget (estimator)

What it's for: Estimate the file size and download time for your onboard connection, and get a SailDocs request sized for that budget. Essential on a satellite link billed per MB.

How to use it: 1. Expand Data Budget. 2. Select your connection at sea (see table). 3. Choose a profile (Micro / Coastal / Offshore / Passage). The app auto-suggests the profile suited to the chosen connection. 4. Read the estimate: grid points, parameters, forecast steps, resolution, estimated size, download time (and $ cost if the link is billed). 5. A ready-to-use SailDocs request is generated: Copy or Open in email.

Options & settings — connections:

Profiles: Micro (sat) · Coastal · Offshore · Passage — from lightest (wind only, low resolution) to fullest.

Tips & limits: An amber warning shows if the file is too large for the connection ("reduce resolution or area") or if the download will be slow ("consider the Micro preset"). On Iridium GO!, stay on Micro/Coastal.

Replaying the GRIB (once loaded)

Views, days and forecast steps

What it's for: Animate the GRIB forecast over time and choose the parameter shown on the map.

How to use it: 1. At the top, choose the view mode: Wind, Pressure or Waves. 2. Select a day (Today, Tomorrow, …) then fine-tune with the time-step slider. 3. Use Play/Pause to the left of the slider to auto-animate the sequence.

Options & settings: - Below the view selector, the sub-options mirror those of the forecast (wind styles: barbs, arrows, particles…; wave sub-modes: height, decomposition, cross-sea…). - The filename shows at the bottom, with a close (×) to clear the GRIB and revert to the online API forecast. - The number of steps and the list of present parameters are shown (source: "GRIB file"). - With a route of ≥ 2 waypoints, a Route Weather strip summarises conditions along the track.

Tips & limits: The animation only plays the steps contained in the file; outside the GRIB's time window or area, nothing is shown. To go back to the online forecast, click the close button next to the filename.

API budget (online)

What it's for: At the bottom of the panel, a used / limit counter tracks your consumption of online weather calls (Open-Meteo and ensembles). GRIBs loaded from the cache or a local file do not consume this budget — which is exactly why they shine on long passages.

Tips & limits: If you approach the limit, prefer reloading from the GRIB cache rather than fresh online downloads.

See also

• Weather layers
• Model comparison
• Ensemble forecast