Marine forecasting


There is an abundance of marine forecasting websites to choose from so what is the best one available?

Like any working mechanism in a marine application, redundancy is always a good thing and the same principle applies to forecasting the sea conditions around the British Isles. Now, we don’t want to be “picking the best forecast” from a range of websites and going to sea on the strength of one, possibly inaccurate, forecast.

The best place to start is the Met. Office website. The area forecasts and inshore waters which are broadcast via VHF and are available via the Met. Office website give a good indication for the day’s expected sea conditions. The “sea state” prediction which goes from smooth, slight, and moderate up to high, very high and phenomenal are excellent indicators of sea state, but they have limitations due to the wide area of coverage and the exact time to expect the predicted forecast to occur. Let me explain. As fronts move in off the Atlantic there are short periods of time between each front when the wind and sea state change and also become relatively calm. Predicting these little “weather windows” and the duration of such can be extremely useful as the duration of the lull could be long enough to make a dash for your next port.

Our next “port of call” on the interweb should be the more detailed forecasts which use data from the Global Forecasting System, WaveWatch3 model and others. Passage Weather and XC Weather are both very good by displaying the wind barbs showing wind strength in 3hourly intervals up to 6 days ahead. Magic Seaweed and Weather Guru are surfing based forecasts but give swell direction and period, along with wind strength and direction for hundreds of surfing locations throughout the country.

For immediate access to the current conditions or if you are waiting for the swell from a previous low pressure system to reduce, XC Weather and the NOAA Buoy Data both give updates, usually every hour, from weather stations and buoys.

If you can install software on your computer, there are a number of free downloads available which give direct access to GFS and WW3 data. These are generally called GRIdded Binary viewers or GRIB viewers. In principle, you select an area on a map you are interested in, select the GRIB parameters which can include, wind strength and direction, barometric pressure, precipitation, snow, CAPE index, temperature, then you select the resolution of the GRIB file you want. For coastal cruising, 1/2 degree resolution is best but for blue water cruising you can use 1 degree resolution which will halve your data download. For 6 days of 1/2 degree GRB file for all of the UK, the file size would be around 200 – 350 kilobytes. GRIB.US, ZyGRIB and other grib viewers are available for free linked from this website. I would highly recommend using a GRIB forecast as the best method of predicting, to a fair accuracy, wind and sea conditions – just make sure your data is up to date. Most GRIB file forecast update every 6 hours.

If you have an Android or Apple smartphone then many of these websites mentioned have apps which aggregate the data into a pocketable format with some of the apps available even offering GRIB file access.

All the websites mentioned above are available directly from this website. I hope this has been of some use to you as you plan your next voyage, usual disclaimer applies.