Saildocs Notes & WARNINGS

De VlmWiki


This grib file is extracted from a computer forecast model. While such computer data can provide useful guidance for general wind flow, there are limitations which must be understood. What you are receiving is a weather prediction generated by a computer run by NOAA/NCEP (GFS, WW3 models) or the US Navy (comaps, nogaps) and downloaded and processed by Saildocs (a service of Sailmail). The network is complex, and any computer network is subject to hardware and software failures or human error which can effect accuracy or availability of data. In particular, if our servers were not able to download a current data file then the grib-file may be based on old data. The file information is shown above and also contained in the file itself.

 Also remember that grib data is not reviewed by forecasters before being made available. You are getting a small part of the raw model data that the forecasters themselves
use when writing a forecast, and it is your responsibility to make sure that the data is consistent with your local conditions and with the professionally-generated forecasts
(e.g. text bulletins and weather-fax charts). 
 Grib data also has limitations along shore, where local effects often dominate and may not be adequately modeled. In addition these models cannot provide adequate prediction for
tropical systems, frontal activity or convergence zones. For example, while global models can provide useful data on the likely track of hurricanes, they grossly underestimate
the strength of hurricanes because of their small size compared to the model grid. For hurricane/cyclone forecasts, carefully monitor the appropriate warning messages and do not
rely on grib data from any source. 
 That all said, grib data can provide useful guidance not available elsewhere. Understand the limitations and use the data carefully. Grib data should be considered supplemental to
other forecasts, and not be relied upon in lieu of professionally-generated charts or forecasts. 

And please save a copy of these notes, they are long and won't be repeated for a month or so.

Thanks for using Saildocs, an Internet document retrieval service for the bandwidth-impaired.

Saildocs is provided without charge thanks to the support of Sailmail, a membership-owned email service for cruising sailors which provides access through a marine-band radio network of 21 stations world-wide, plus internet and satellite gateways. For more information on SailMail see the web page at or send a query to the office at

More information on Saildocs is available by sending an email to, this will return the how-to document (about 5K).