Weather

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Revision as of 04:20, 4 August 2014

Weather

As seamen, we are heavily dependant upon the weather. As sailors, it is our motive force. This page is devoted to wind and waves and the weather patterns that make them.

Also See

• Extreme Weather

Weather Tools

Weather Models

All weather forecasts are dependent on one or more weather models. These are computer simulations of the weather produced in various places and by various agencies around the world. The wikipedia page on numerical weather prediction gives an overview of some of these models.

Common weather models in use include:

• GFS or the Global Forecast System, run by the US National Weather Service.
• The GEM or CMC model run by the Canadian Meteorological Centre.
• The UK based Unified Model.

Weather Data

Weather information comes in one or more of the following formats, which can be either human-readable or computer-readable. Computer-readable means that the data can be loaded into a computer program for viewing the data, whereas human-readable means that the data is designed to be displayed as-is on the computer screen for interpretation by a person reading the file.

• Text format weather forecasts, for example "Winds E/SE at 15-20 knots, easing to 10-15 knots later". These are human-readable files issued by many weather agencies around the world covering the area of interest of the agency as well as some related areas. For example the Australan Bureau of Meteorology issues data covering Australia and surrounding coastal water and ocean areas, whereas the Fiji Metorological Service issues weather forecasts covering most of the South Pacific.
• Weatherfax data, which is human-readable pictorial data submitted as image files over HF radio or similar. Weatherfax data is issued by many of the same agencies that issue text data, and broadcast over HF from a number of HF radio stations around the world. The definitive guide to these is contained in the book Worldwide Marine Radiofacsimile Broadcast Schedules' issued by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Weather Service (NWS).
• GRIB are computer readable data files that can be loaded into navigation software. These are based on weather models, often the GFS model issued by NOAA, or the CMC model issued by the Canadian Meteorological Service, and made available through a number of internet GRIB file retrieval services.
• Similar to GRIB files, SPOT files are human-readable data files showing the wind, wave, temperature, pressure or other forecasts over a period of time. These have the advantage of being smaller than GRIB data files where a specific point forecast, rather than an area forecast, is required.
• IAC Fleet Code format is either human-readable or computer-readable, depending on which way you look at it. The fleet code data is a set of information in five number code groups which can be used to hand-draw weather maps by connecting the dots to show the location of pressure, frontal and tropical systems. Fleet code data is issued by two bureaus, currently the Fiji Metorological Service issues data covering the South Pacific, and NOAA which issues data covering the North Atlantic.

Computer Programs to Display Weather Data

• There are a number of programs that can be used to display GRIB data, some of which include automated downloaders (which may not be suitable for use at sea where only email is available). It is also possible to load GRIB data into many navigation software suites including OpenCPN.
• There are currently 2 programs that can be used to display IAC Fleet Code data, which are physplot by Pangolin, which runs only on Windows, or alternatively zyGrib which is cross-platform but only works with the NOAA Fleet Code data (and includes a built-in downloader).

Methods of collecting weather data

The method you use to collect weather data depends on the format you wish to receive it in:

Text Forecasts

• NAVTEX - receives forecasts for most areas up to 250 miles offshore. See www.pcnavtex.com for more information.
• Saildocs offer text forecast retrieval via email.

Weatherfax Data

• See Weatherfax

GRIB Data

Downloading GRIB data is usually based around an email retrieval service. In order to be able to set that up, see Email at Sea. Once you are able to send and receive emails, there are a number of email based GRIB data services available:

• SmartMet - download and view forecasts from GRIB files, as well as satellite images and current weather reports. See www.smartmet.co.uk for more information
• Saildocs is one of the first document retrieval systems designed for use by those with limited bandwidth. It offers a GRIB file retrieval service supporting the GFS weather model. Data from other NOAA and US Navy models is available, send a (blank) email to: [email protected] for details.
• Global Marine Networks offer a free GRIB file retrieval service. Their forecasts are based on the National Weather Service, NOAA, Wave Watch III model

References

Books, etc.

Forum Discussions

Links to discussion threads

External Links

• National Geospacial Intelligence Agency's Pilot charts - Free pilot charts and other info.

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