Sources of weather and oceanographic data

The data referenced below is available from Saildocs, Great Circle-Squid or Expedition. These are the main sources of data used by the sailing community and are all available in Expedition. In addition, much data is feely available on the internet, especially for US and European waters.

Saildocs is a free source of grib data designed to satisfy Rule 41(c) and can be used to retrieve other information.

Great Circle - Squid is a complete weather service with satellite images, observations and model data. Offical supplier to the Volvo Ocean Race.

SailFlow is a source of weather observation data.

Expedition has an integrated grib server, mainly to provide data not available from Saildocs or Squid. For example, GFS 1/9°, UM-Global, ICON, ECMWF HRES and Ensemble, GDPS, Arpège, NBM Oceanic and Copernicus Mercator.

Expedition also supports several other services and has links to freely available observation and model data (MyGrib and MyImage).

Important note

Whilst racing, services such as routing or weather data that is not free of charge or easily available to all boats are not allowed by Rule 41(c) (outside help) of the RRS. See Case 120 in the Case book. However, Case 120 clarifies that rule 41c may be changed for any particular race by the notice of race and sailing instructions.

Weather maps and observations

Weather maps, satellite and radar imagery are available from many sources, including MyImage in Expedition and Squid.

Weather observations are available from many sources, including BOM, NOAA NDBC and SailFlow in Expedition.

Expedition supports Rainviewer radar data. Rainviewer is a free service, so we encourage people to support them with Patreon.

Windy may be the best of the online weather viewers, with GFS, ICON, ECMWF, Arôme & NAM data. It is also available as Android and Apple apps. Flowx is another very nice app and includes Expedition WRF data.

Grib data

Data and sources we have found useful over many years of racing:

Global models

From experience, 0.25° is a good compromise for global model data offshore

0.5° is usually too coarse, but is an option for slow connections.

1/8°-1/10° data may be more useful, but file sizes will be larger. Doubling the resolution will increase file size by about a factor of 4

Comparing models

Comparing models is difficult

One model will never always be better than the others and the task for the navigator is deciding which, if any, is most appropriate for the day.

Model Accuracy can be useful to compare how different models performed during a race or at a given location. Of course past performance isn't always a good indicator of future performance ...

Another very important aspect is timeliness. The sooner the data is available, the more useful it is. Although starting the model run earlier will miss late observational data.

The Expedition server update status can be queried from within Expedition. As a general guide, data starts to become available after about these times after the main synoptic hours:

ICON 0310
GFS 0410
Arpège 0400 (varies)
GDPS 0430
UM 0440
ECMWF 0710
ECMWF Ensemble 0810
NBM varies
Mercator 1000


13km resolution and 127 levels
Available 4x daily at 1/9° or 1/4° resolution to 384 hours


10km resolution and 70 levels
Available 4x daily at about 1/10° resolution
00 & 12z runs are available to 168 hours, 06 & 18z runs to 60 hours
UK Met Office - Powered by Met Office Data


13km resolution and 90 levels
Available 4x daily at 1/4° or 1/8° resolution
00 & 12z runs are available to 180 hours, 06 & 18z runs to 120 hours
ICON data is generally available earlier than GFS and UM
DWD Germany
Licence and copyright


9km resolution and 137 levels
Available 4x daily at 0.4° resolution
00 & 12z runs are available to 240 hours, 06 & 18z runs to 90 hours
HRES is a medium range model, so is available later than other models
Licence and copyright


15 km resolution and 84 levels
Available twice daily at 0.15° resolution to 240 hours
Environment and Climate Change Canada, licence terms


7.5-37km resolution and 105 levels,
Available at 1/2° resolution globally and 1/10° for Europe
Available to 60, 72, 102 or 114 hours depending on run
Meteo France
Licence and copyright


T681 (about 20km) and 60 levels
US Navy model


National Blend of Models - a blend of many models
Available 4x daily at about 10km resolution (NBM Oceanic)

Regional models

The local government high resolution models are generally very good and are usually the default choice

Expedition also provides WRF simulations for areas where high resolution data is not available or hard to obtain. They can be also useful as a second forecast for comparison.


BOM Access
Expedition WRF



Cape Town

Expedition WRF


Expedition WRF


Arôme & Arpège
HIRLAM & Harmonie, FMI, KNMI &
SMHI Sweden
Expedition WRF, some areas are on demand for regattas

Japan, Hong Kong, Philippines

Expedition WRF, on demand
Hong Kong tidal current data

New Caledonia and Polynesia



Expedition WRF


NOAA HRRR, RAP & NAM. HRRR is very good
GLERL - Great Lakes winds and currents
Expedition has integrated current models for various areas

Ensemble forecasts

Ensemble forecasts are used to help understand uncertainty in forecasts

Ensemble forecasts consist of an unperturbed control run and a set of perturbed members, in which the initial conditions and model physics are perturbed from the control run. For the ECMWF Ensemble forecast, this consists of a control and 50 perturbed members.

On average, each of the perturbed members will have lower skill than the control or deterministic forecast, although any individual forecast might show a higher skill.

Examples include ECMWF Ensemble, UK MOGREPS, NOAA GEFS and CMC GEPS.

ECMWF Ensemble is available from Expedition. Licence and copyright.

GEFS is available from Great Circle-Squid.


Copernicus Mercator

Global ocean currents, available at 1/12° resolution
Higher resolution data available for north west Europe and the Mediterranean
Copernicus Marine Environment Monitoring Service


Ocean currents and sea temperature, available at 1/12° resolution


Wave model

BSH Baltic & North Sea tidal currents

Expedition has integrated current models for various areas, including Proudman European tidal currents and SHOM tidal currents for France


Copernicus ERA5 hourly data on single levels from 1979 to present

Licences and attribution


  1. Copyright statement: Copyright "© European Centre for Medium-Range Weather Forecasts (ECMWF)".
  2. Source
  3. Licence Statement: This data is published under a Creative Commons Attribution 4.0 International (CC BY 4.0).
  4. Disclaimer: ECMWF does not accept any liability whatsoever for any error or omission in the data, their availability, or for any loss or damage arising from their use.
  5. Where applicable, an indication if the material has been modified and an indication of previous modifications.

Copernicus Marine Environment Monitoring Service (CMEMS)

  1. Licence
  2. Global ocean analysis and forecast
  3. Mediterranean Sea analysis and forecast
  4. Atlantic - European North-West European Shelf analysis and forecast