Saildocs GRIB code service

A basic GRIB data service is available from Saildocs. Files are extracted on a per request basis from the US NOAA/NCEP global GFS computer model and can cover any requested area, worldwide. The resulting file size depends upon the amount of data requested but can, in principle, be  anywhere from 1 kb to megabytes. For most normal cruising requirements, file sizes of a few kb may be sufficient and need not exceed 10 - 15 kb.  Radio email services are available using Airmail software on one's laptop in conjunction with either the Winlink or SailMail systems, or even both. (Currently, SailMail will now handle GRIB files up to 10 kb for Pactor-2 users, and 30 kb for Pactor-3 users.

For detailed information for use with Airmail see the Notes on using Saildocs

provided by Allan Riches of Brunei Bay Radio. Also see the page produced by Richard Clifford for members of the RCC. for information on the use of Airmail by HF radio..

Output is available up to 16 days ahead although I would only recommend using up to 5 to 7 days which I regard as a reasonable limit for useful (rarely accurate) forecasting although this limit is slowly being pushed out beyond that time.

The US NWS runs its computer model 4 times a day using data at 00, 06, 12 and 18 hours UTC.  A note concerning the output issued by Saildocs is on another page..

Requesting a GRIB file

The procedure described here uses Saildocs and is somewhat cumbersome to use but extremely flexible.  

The format for a Saildocs GRIB request is a little cryptic. Follow the instructions below carefully. The format, which MUST be exactly followed, for a basic GRIB file request is:

 send gfs:lat0,lat1,lon0,lon1|dlat,dlon|VTs|Params

lat0,lat1,lon0,lon1 are the latitude longitude limits (whole degrees followed by N/S or E/W

NOTE the "gfs" can be replaced by "GRIB". the result is the same, except for the way in which date/times of forecasts are shown. Experiment and choose which you prefer.

dlat,dlon is the grid increment in degrees (e.g. "1,1" for a 1-deg by 1-deg grid), if omitted the default is "2,2", The minimum increment is 0.5 degree

NOTE. The 0.5 degree data might not always be available. This is a result of the route by which SailDocs extracts the information from the NOAA system.

VTs is a comma separated list of valid times (e.g. "24,48,72"), if omitted the default is "24,48,72". Available valid times are 0, 3, 6,12,.........180 hours on a 0.5 degree grid. 192,204..384 hours on a 2.5-deg grid.

Available Params are PRMSL for mean sea-level pressure, WIND for the gradient surface ((10-meter) wind, HGT for 500mb height, SEATMP for sea-surface temp, AIRTMP for air temperature (2M altitude), and WAVES for wave-height (from the WW3 model).

The model data is updated shortly before 06:00z for the 00z model-run and every 6 hours.

For example, to request a GRIB file which covers 20N to 60N and 0E to 20W, on a 2-degree grid for valid times of 24 to 72 hours, containing  surface pressure and wind, send the following email to query@saildocs.com

Type anything you wish as subject - but do not leave it blank.

Then, in the message type (do not forget the word send).

send gfs:40N,60N,0W,20W

Note that this is identical to:

send gfs:40N,60N,0W,20W|2,2|24,48,72|PRMSL,wind

IMPORTANT: Do not insert any spaces, Saildocs uses spaces to delimit parameters. The vertical bar character is the shift backslash key. There is not much format checking done, and it is not user friendly.  At some stage the system may be revised so that requests are generated with some sort of fill-in-the-blanks window, similar to that used by Navimail.  At this stage it is probably best to copy the above formats using Edit - Copy and then amend details of  location and  times as required.

For simplicity, copy and paste the above message, then put in your own values for Lat, Lon, the times and the spacing - ie I often use 1,1.

Data from other NOAA and US Navy models is available, send a (blank) email to: gribmodels@saildocs.com for details.

NOTE re Word-Wrap

It is essential that the whole message is on one line of the email message. This is because the CR/LF acts like a space and is a delimiter. This is particularly important to note if you ask for a large number of times and use requests for repeat messages.  In Outlook Express - use Tools - Options - Send - Mail Sending Format - Plain text settings. Ensure that the automatic Wrap text figure exceeds the number of characters in the request.

A long request-line can be broken with a "=" character as follows: send gfs:20N,60N,160W,120W|2,2|6,12,18,=
24,36,48,72,96|PRESS,WIND time=12:00

A shortcut is also available for a long list of forecast-times, for example: send gfs:20N,60N,160W,120W|2,2|6,12..96|PRESS,WIND
This means 6, 12 hours and then repeat the same 6-hour interval out to 96 hours.

The ",...," must appear exactly as that, ie  comma-dot-dot-dot-comma -and tells Saildocs to repeat the previous (6 to12) interval out to 96. This should allow any command to fit on a single (short) line. 

Loading and Viewing

Having received the email reply, save the attachment to a folder.  Open Viewfax by double clicking on the icon, then use File - Open.  It is then possible to view the charts in sequence or at random. A chart viewed using Viewfax will look like this:

NOTE. One short feather = 5 knots, one long feather = 10 knots.  The arrows "fly" with the wind.

Repeat Requests and Cancellations

For a daily repeat, use the same format but change the "send" to "sub".  For example: send the following email to query@saildocs.com

 Subject: anything you like

Then the following message

sub gfs:40N,60N,0W,20W|1,1|24,48,72,96,120

This will enter a request which will be replied to daily,  shortly after 0615 UTC. The area is 40-60N, 0-20W, spacing is 1 deg lat/lon and times are for 1, 2, 3,

4, 5 days ahead.

By default you will receive this information daily for 14 days. To change this add a space and "days=5" for a 5-day subscription, or "days=0" for an indefinite subscription, for example:

sub gfs:40N,60N,0W,20W|1,1|24,48,72,96,120 days=5

To cancel a request, send the same message except change "sub" to "cancel". The GRIB code must match exactly, even if it is incorrect.