Getting weather info: What you need, how to get it
There are three basic types of weather data: Text bulletins, grib data, and weather charts. This note will describe the best usage of each and how to obtain them via Sailmail.
Weather forecasts are produced by most of the countries in the world for their local area including national waters, and the larger countries take responsibility for the oceans of the world. Not all are created equal however, and not all forecasts are readily available.
Saildocs is Sailmail's weather server, which provides bulletins and grib data available via email and also by direct internet via our "Viewfax" software for Sailmail members.
Text bulletins:
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Written weather bulletins contain warnings and forecasts and are available for most oceans and coastal waters. The warnings are important part here, the forecasts-- especially offshore-- tend to be very general and limited to just a few days. These bulletins are generally small in size and readily available via text email, requested from the Saildocs catalog (Airmail's Windows menu, Catalogs).
The most general high-seas forecasts are the "Met Area" forecasts. Metarea forecasts are found under "Metarea" in the Saildocs catalog. These are produced by the country responsible for each area, and vary in quality and detail. A map showing the various Metareas is on the web at http://weather.gmdss.org/metareas.html
Coastal and offshore forecasts are also produced by various national Met services, those that are known are indexed in the Saildocs catalog under various regional categories.
Any of these text bulletins can be requested as a single copy, or "subscribed" to for a daily copy (or more often) sent automatically. The Saildocs catalog allows the time and interval to be specified, and copies are only sent if the text of the bulletin has changed since it was last sent.
Tropical storm bulletins from NOAA's national Hurricane Center (NHC) consist of various bulletins for five named storms, labeled "storm #1" through "storm #5". These codes are used on a rotating basis as each new storm is identified. Using subscriptions makes this easy to manage: In the Saildocs catalog, under "Tropical" and "Atlantic", subscribe to all five "Atlantic Public Advisory" bulletins (for example), for 180 days (or however long is relevant) to be sent every 1 hour at 00:00 utc. Saildocs will send a first copy, then check the bulletin every hour. If the bulletin has changed then Saildocs will automatically send the updated bulletin. If you don't pick it up before it changes again then the Sailmail server will replace the old copy with the newer one.
In summary: text bulletins offer little detail, but are easy to get and are very important because they will include storm warnings.
Grib data:
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Grib (gridded-binary) files are coded weather-data files, which display weather maps when opened from Airmail. Gribs do not contain explicit warnings other than your interpretation of the data, but do provide great detail and forecasts well beyond the practical limit of 4 to 6 for reasonable accuracy.
To request a grib file, open the Saildocs Catalog, select the "Grib Files" catagory on the left, and verify that "GFS" is selected below the map-- that is the global forecast model.
Move the map around with the slider-buttons (bottom and right edges), and zoom buttons ("+", "-"). Click-and-drag to create a blue rectangle, that is your lat-lon area selection. Now click "Request", this opens a new box with details of your grib-request.
For a first request try this: In the "data grid" box (lower-left) set delta-lat to "2" (2 degrees between data points). Set forecast time to 6 or 12 hours, days to 3 to 5, and select "PRMSL and "WIND", pressure and surface wind. Check the size in the lower-left, 10K or less is a good size to being with. To reduce the file-size change 6 hours to 12, or increase delta-lat. Click "Post request", connect and retrieve your file. The reply-message contains the data file, double-click it to open it in the viewer. Also read the notice info in the message.
The GFS model is the primary global model, but other data is available: NAVGEM is the US Navy global model, not considered as reliable but useeful as a "second opinion". (ECMWF is the other major global mode but unavailable without large fees). WW3 is the global wave model, but the basic wave parameters can be included with a GFS request. COAMPS is a regional model for NE Pacific and NW Atlantic, higher res and shorter forecast times. RTOFS is a global current model, and OSCAR shows historical currents for the past 5-days, updated every 5 days.
The NDFD forecast is important, because it is the only forecaster-generated weather forecast available in grib format. This is experimental and limited in coverage and duration, but a valuable source for shorter-term forecasts within the coverage area.
More information on available grib models is available from http://saildocs.com/gribmodels or by sending a (blank) email to: gribmodels@saildocs.com
Weather charts:
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You can also copy broadcast weatherfax via Airmail's fax window, which uses the same pactor modem except in a special fax mode. Fax charts are a US Coast Guard broadcast (from the states), not Sailmail, and doesn't use any Sailmail time. Power on the radio and modem, click the "fax" button instead of terminal window, select the Boston (Marshfield) station, select a frequency and copy the chart. You can just let it run, Airmail will copy each chart and stick it into your inbox. Same schedule as a traditional fax machine, click the "clock" button in the fax window to open the (PDF) fax schedule.
To receive a weatherfax image, find the appropriate station and note the times for the charts you want then open Airmail's fax window (fax button or Modules menu), select the station and frequency and let it run. It will start and stop automatically, and save the received images as incoming messages. You can change frequencies as the fax is being received, to get the best image. Most stations transmit charts in a block, one chart every 10 min's or so, so just copy the whole block and sort out what you want later.
These weather charts are image files, too large for sending by email via radio connections. However satellite users can retrieve images via email with the latest Airmail versions, under "Images" in the catalog. Note however that the files are still large, so will take 2-3 minutes per image via Iridium for example which adds up to a lot of airtime cost (unless you have an Iridium GO with the unlimited data plan).
revised 2016-11-18 Jim Corenman