An Essential Marine Forecast Page for Sailors

Many sites on the Web give weather links and range widely over the science. Some are listed at my General Weather and Sailing Links page. I have tried to point to sites that are likely to be of help to sailors and to give alternatives because sites do have problems from time to time. I have also tried to indicate the uses to which some of the information can be put.

The target is very much a moving one and I will try to keep this and other pages updated although the links will never be exhaustive or definitive. I will try to answer queries but I am likely to be away sailing for long periods during the "Summer" half of the year. Short emails will help my cell phone bill. Comments on the links on these pages, particularly their availability may be sent either to Frank Singleton or to Martin Stubbs.

Links to meteorological information on the Internet are not guaranteed and therefore must not be relied upon. Although increasingly reliable, the Internet is not part of an operational service, pages can and do change at no notice - even on official Met service sites.

ISPs can and do take their systems off-line for maintenance with no prior warning. In particular, the system should never be relied upon as a sole source of information when at sea. In an operational sense, it is supplementary rather than complementary to the GMDSS.

Although satellite phone services are reasonably reliable nowadays, those using cell phone can have reception problems around the coast, say weathern Scotland and beyond a few miles out to sea. improved aerial systems can help but, for such occasions as distress calling and helping others in difficulty, there is still a place for GMDSS communications.

Many sites provide information that has copyright restrictions and, in general, the information must not be used for commercial gain unless permission has been obtained either from the Meteorological Service concerned or from the provider of the information. All links are believed to be correct when provided. I cannot guarantee that they will remain so.

The two main world centres are the UK Met Office and the US National Weather Service, Washington, which provide, by mutual backup, the worldwide service to aviation. Their numerical weather prediction models (NWP) are probably the most advanced in ‘’’operational’’’ use. That is why many sites lead inevitably to products originating from the UK Met Office or the US NWS.

There are, of course, many other Met Services, see the pages on ECMWF and other Weather Centres and the links to International and National services.

Many of these organisations run NWP models and, for various reasons, output will differ from one to another. Comparison between models is a useful way of gaining impressions about the value of a forecast on a particular occasion.

Charts come in three forms.

• First, and most familiar to many, are charts that have some human input in the drawing of the isobars and fronts so that there is experience added to the computer output.

• Secondly, there are charts which are unadjusted computer output of the predicted pressure fields, but with fronts added by a forecaster.
• Finally, there are charts which are pure computer output of mean sea level pressure, and various upper air fields, these being un-amended by a human forecaster.

Weather forecasts in text for the open sea are provided under the SOLAS Convention, by nominated countries worldwide. These can be obtained by VHF, MF and HF Radio, NAVTEX, INMARSAT-C and, nowadays, via the Internet.

More localised Inshore waters forecasts are usually produced by relevant countries and broadcast on marine VHF, sometimes by NAVTEX and on the Internet. National Weather Services producing these forecasts have access to the various NWP models so that these forecasts should be well founded.

This is one of the leading National Weather services/ The Met Office Home page, includes its scientific programmes with detail about weather prediction models, climate change research, observations and so on. There are also some forecasts, including movie loops of charts, and satellite pictures. Abbreviated Hourly observations from United Kingdom land stations are available including a one week archive of the data. There is a similar archive for Global Data as well as a specialist Marine observations page.

For those who want to learn some basic synoptic meteorology, there are some useful pages on the site. These page are commendably clear and should be part of any Yachtmaster, Coastal Skipper or Competent Crew course notes.

There are good pages on identification of clouds, how they are formed and the associated weather. Some links to Met Office information pages and forecasts are as below.

The UK Met Office Analyses (ASXX) and 24-hour prognoses (FSXX) for 00, 06, 12 and 18 UTC are issued every six hours. The analyses are now usually available on the Internet some four hours following the data time and the 24-hour forecast charts after another hour. The Prognoses are based on the computer output, but amended by forecasters in the light of their knowledge and experience. See the page on Numerical Weather Prediction (NWP) to read more about computer output.

The UK Met Office Prognoses for 36 hours to 72 hours are produced in the same way, but only issued twice a day using midday and midnight data. They are available on the Internet some 6 or 7 hours after the data time..

Prognoses for 96 and 120 hours are issued once a day at about 2300 UTC. These 4 and 5-day forecasts are based on the UK Met Office computer model but with a long sideways look at output from other Met Services output, including that from the ECMWF, the US NWS, France and Germany. The product issued is a 'preferred' solution for the fourth and fifth day and may differ considerably from the raw computer output from the UK computer model.

There are several sources for these charts and, if one link fails, then another may work. The size of each chart is about 60 Kbytes which is significant if using a mobile phone connection. To help those with limited bandwidth there are small versions. See my page of charts on the Internet.

These charts are UK Met Office NWP output simply with the addition of fronts. They also show areas of rainfall and extensive cloud. These cloud areas are those expected due to fronts, and other large scale uplift of air that occurs with areas of low pressure, rather than areas of convection cloud. Apart from the cloud, the rainfall areas and the colour presentation, these charts should be very similar to those on MetFax. The addition of cloud areas makes these charts somewhat "fussy" and some might find that it detracts from their usefulness.

The site contains links to give 5 day forecasts for USAF bases in Europe and for European cities.The updating of the charts via Sembach is based on operational requirements and can be rather variable. It is quite often possible to get more up-to-date charts from the UK Met Office or by accessing the more specialised computer output from the UK Met Office NWP model.

See the chart page for Analyses and forecasts from Sembach

A particularly useful site of all is the US National Weather Service Marine forecast pages. Charts from the US and many other centres can be found on several good sites, such as the Georg Mueller's site and the Institute of Global Environment and Science site.

Meteosail has a well laid out and comprehensive set of links to charts of vector wind arrows and a miscellany of other information worldwide. Apart from a few areas, it is not clear which weather service or services have provided the wind vector information. Clearly, they must be from one of the major NWP models, most probably the US GFS model. Other data sources are obvious from the product shown.

The US Navy site has a number of products of interest to sailors. Some eg UK Met Office Charts replicate what is already on this page. One very useful product is a set of charts giving isobars and wind vectors. These are from the US Navy NWP model known as NOGAPS found, for example, at Georg Mueller's site

The home page of the Fleet Numerical Meteorology and Oceanography Center gives numerous links to their charts worldwide. Downloads are a bit slow but, if time is not a consideration, this is a useful site. Click on Global Models, then select an area and a menu will appear. This lets you select a type of chart and a time up to 6 days ahead. Sailors will find the charts labelled Sea Level Pressure and Wave Watch Significant Wave Heights to be the most useful.

An easy to use service is provided by PassageWeather to advertise other services. Their chart service comprises charts of vector winds fusing GRIB files the US GFS model, An excellent "Jumbo site" for charts from many sources is Ogimet.

NOTE - The USA gives wave height in feet. UK and DWD charts use metres.

These charts are raw (ie unmodified) computer forecasts from the 00 UTC and 12 UTC runs of the UK Global Model The charts are surface isobars PLUS the flow at a height where the pressure is 500 hPa. These charts are very much for the professional meteorologist although they do give a useful outlook out to six days ahead, twice a day. In particular, the isobars are clearly shown.

The 500-hPa pattern is represented by a series of colours (a key appears on the side of the panel) while there are also the key 1000/500hPa thickness lines (e.g. 510, 528, 546 and 564 hPa) on these charts.

The thickness is the difference between the height at which the pressure is 1000 hPa and that at which it is 500 hPa and it is a measure of the average temperature of the whole layer. Hence the forecast 1000/500hPa thickness can be a guide towards expected temperatures and whether precipitation is likely to fall as rain or snow (more details in text-books on meteorology). Charts are usually available some nine to ten hours after the data times of midnight and midday UTC.

ECMWF is a research organisation funded by 23 European Met Services and was charged, initially, with developing forecasts out to 10 days or more ahead; in addition, they include seasonal forecasting. They now run their computer model twice a day but rather later than the Met Office and other operational centres. Charts on the open part of their site go from 3 to 7 days.

It is useful to compare the output for T+120 and T+144 hours with charts for the corresponding time from UK Met Office and other centres. If they look broadly similar, then it gives some indication that the forecasts are on the right line. If they differ greatly then in suggests that the weather is in an indeterminate mood.

Go to the MRF charts on Georg Mueller's site. Against the Sub Head 500 hPa. Bodendr, click onto the period that you want eg 240 hours = 10 days or, quicker, onto 9-panel film. The quality of the longer period charts is not terribly high and it should be noted that ECMWF, UK Met Office and the German

Met service do not issue any charts beyond 144 hours ie 6 days ahead.

Anything beyond 6 or 7 days really is entering the realm of scientific speculation at this stage. Caveat emptor - except that the charts are free on the Net! Using the US NWS GRIB coded service, predictions can be obtained out to 15 days ahead.

The UK Met Office forecasts provides the definitive marine forecasts for waters around the UK. Other countries' services such as Météo France do likewise for their waters. Go to the GMDSS page where there are also links to most marine text forecasts around Europe.

Because many British (and other nationalities) sail in the Baltic and the Mediterranean, this site has pages listing all forecast sources that I believe are useful for the Baltic and the Mediterranean. Because Iceland is out on its own and has a very good service it has its own page..

There are a number of sites run by private weather companies where forecasts are available. Sometimes these are free and sometimes they are on repayment. I have always hesitated to give links to such services because I do not know to what extent these forecasts are based on the National Met Service output. Neither do I know the levels of experience and training of the staff. The presentation of forecasts by the private companies are often very good.

A service that I can recommend because I know some of the people is WeatherWeb. They provide a "talk to a forecaster" service and also run a Weather School.

Wherever they come from all forecasts from private companies should be used with the same care as those from the National Met Services.

Normally, weather observations from land stations are made on a regular basis. For many stations this will be every hour. on the hour. Where the observation depends upon a human observer being present then the reports may be less frequent. Automated observing is increasingly coming into use and at some places the content of observations will vary depending upon whether there is a human to describe the cloud and weather or not.

At airports and military airfields there may well be more frequent observations, perhaps every 20 minutes, while the airport is open.

For information on automatic observing, see the page on wind measurement and visibility observing. For UK land stations, go to my actuals page.

There are four forms of marine observation, from ships of opportunity. tethered buoys, drifting buoys and wind observations derived from low orbiting satellites.Voluntary observing ships have made observations of weather on a routine basis since the 1850s. The data are most useful both as an everyday operational resource and as the basis of an invaluable global archive. Ships normally report on a six hourly basis at 0000, 0600, 1200 and 1800 UTC.

In the days of single manned radio operation, data were received mainly at during daylight hours, 1200 and 1800 over the N Atlantic and at 0000 and 0600 over the Pacific. With modern communications from a keyboard, used by officers of the watch on the bridge, there may well be a better coverage throughout the day. However, decreased manning levels has led to some decrease in observations when ships are in busy waterways. There has also been a serious decrease in the number of VOS from 7000 in 1999 to about 4500 in 2008.

Tethered buoys can only operate on the continental shelf in a depth of water not normally over 2000 metres. In the same category, come observations from light vessels, remote islands and oil or gas rigs.

The data are from automated systems and may include sea state. At oil rigs there may also be some human component to the observation. For commercial reasons, rig reports might not always be available since they might be used to give some indication of operating problems. Most data buoys around the UK provide data on an hourly basis.

Drifting buoys are cheap, use once and be prepared to throw away, systems that normally only give pressure, and sea temperature. They are dropped into the ocean at strategic locations and then drift with wind and current. Data collection is by satellite and depends upon the time of the over-pass. Each buoy costs a few £1000s compared to the more versatile tethered buoys that cost around £100k.

Satellite measurements of sea surface winds are made using the scattering of a radar wavelength beam. This measures wind speed pretty well but with a directional ambiguity. This is normally resolved through a quality control process involving internal consistency, data from other sources and the short period forecast. Data are unreliable where there is rain but this is indicated on the display charts of these "QuikScat" data. The technique does not work near to the coast.

Paying for weather forecasts is not confined to the UK. In France, for example, there are various services available from Météo France by telephone and Minitel or from Météo Consult, many at prices similar to those in the UK. Usually, some information is freely available as broadcasts by Coast Guards and MRCCs. Free information on many Web sites is either paid for by advertisers or is there as a "loss leader". In this world, there is no such thing as a free dinner!

Under the SOLAS convention certain weather information is available free of charge at the point of delivery.

The minimum requirements are for 24 hour forecasts plus a brief outlook for sea areas to be broadcast on NAVTEX and INMARSAT SafetyNET^TM. . Within the spirit of SOLAS, but going beyond the minimum, the UK Coast Guard currently broadcasts Inshore Waters forecasts four times daily on marine VHF, and on MF. Likewise around the coasts of most European countries. In a very welcome change of policy, the UK, like both France and Spain makes the same texts available on the Internet as a free service in the interests of safety.