The gruppenfuhrer of weather sources is Frank Singleton with his Weather
site for Sailors. He has recently improved his Baltic coverage and is completely comprehensive
on how to get information afloat. The following section summarises my experience, but I suggest you use Frank’s site as the main
jumping off point.
The DWD (German Met Office) are probably the most accurate predictor
for the region, as like the French and the Brits, they run their own Weather model. They publish two day, and three day forecasts on the Web. They are in German,
but the language is easy to pick up.
Also on the Web, the Danish Met office (DNI) has recently updated its site. It publishes forecasts in English for sea areas up to 1
day ahead, and general area forecasts for up to 5 days ahead. It also
publishes accurate graphical wind
flow forecasts (just select your sea area). In Sweden, coastal forecasts are available by VHF or on the Web.
The most useful invention for the cruising sailor are GRIB files. Sailmail, a cooperative venture between sailors and radio hams, has an automatic system which will
extract wind forecasts from the US model and email them to you. The major advantage, apart from being a free service, is
that the files transferred are small, as you use separate viewer to access the files. This keeps costs down if you are accessing
the net via a mobile. The downside is that the data is not interpreted by a human, so you run a little risk. Some charting
systems (e.g. Transas) incorporate a GRIB viewer, or you can download one from the downloads section on the Sailmail site. Full instructions on how to use these things are
on the GRIB section on Frank’s site.
We've found that Sailmail works reliably, and is generally pretty accurate. Our observation
is that if anything it tends to underestimate the wind slightly, and the absence of weather fronts on the charts is a pity as you cant tell if its going to rain!
The situation has improved in the last couple of years with the advent of GRIB.US. This uses the same weather sources as Sailmail, but provides an enhanced and much easier to use viewer, which can be used to download the files interactively. The GRIB.US files include rain information, from which you can often infer the missing fronts. It also has a very useful metogram facility. Although the initial package download is large, and needs the even larger Microsoft .net package (no Mac facilities as yet), the file transfers are comparable. In fact, you can view the Sailmail fies in GRIB.US's viewer, and vice versa.
The Germans use Beaufort forecasts, but all the wind forecasts in Denmark and Sweden are in meters/sec, rather than knots. A sufficiently
accurate conversion to knots is to multiply by 2 i.e 10 m/s
= 20 kn or, for a good approximation, divide m/s by 2 to get the Beaufort force.