GRIB files in GPSNavX and MacENC

Posted on Auteur Francis

The menu Weather report in these two applications allows you to request a GRIB weather forecast file and then view it on the open map. The function Request GRIB send a request to the server Saildocs.com returning to the mailbox file requested. You can then get the file in attachment and store it to the location of your choice (²).

The function Show GRIB will then allow you to view the file on the map and scroll through the forecasts. You can usefully refer to MacENC Video Tutorial No. 3 on the website.

Here is a short technical summary of the weather module integrated in these two apps.

Types of data

There are several types of data to choose from :

  • Surface wind and Pressure
  • Surface 500 mb
  • Waves (Height and Direction)
  • Water Temperature
  • Air temperature
  • Precipitation rate

In GPSNavX : Forecasts are provided by intervals of 12 hours out to 3 days. The files cover a 50 ° x 50 ° area, corresponding to the chart displayed at the request (Minimum scale 1/750.000).

In MacENC : Three sub-menus allow you to define the characteristics of the files :

  • Out to : 3, 5 or 7 days
  • Intervals : 3, 6, 12 or 24 hours steps
  • Resolution (grid) : 0,5°, 1,0° or 2.0°
The size of the downloaded files and therefore the cost of transmission will depend on these choices (i.e.. Satellite phone).
The files cover a 50 ° x 50 ° area, but the function Reduced area, if checked, Reduces the area to 20° x 20°, to limit the file size.

Which forecasting models ?

All prediction come from GFS 0,5° NOAA except waves that originate from the WW3 1,0° (¹).

However, since version 8.10, MacENC adds a Surface wind / pressure request with high-resolution model COAMPS from the U.S.. Navy (¹), with a resolution of 0.2 ° (12 nautical miles) with 6 -hour steps range up to 48 hours steps, and this exclusively for the three zones below :

 

zones US COAMPS

Zones U.S. COAMPS

Remarks :

MacENC uses the mail protocol as many yachtmen use the email wireless service XGate with a satellite phone at sea to download GRIB files. This also applies to other access providers (Vizada, Geolink, MailaSail) Moreover, The advantage of using an email connection is the support for mid file restart, in the event the sat phone connection is lost during transmission.

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(¹) See " Forecasting Models " in the Glossary for technical explanations.

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Related articles :
(²) Receiving GRIB files in GPSNavX and MacENC
On website : Weather files 1/2

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