INTRODUCTION
This article explains GRIB files and how to access them by email.
GRIB is an ancronym for “General Regularly-distributed Information in Binary form”, which is a mouthful. It's actually a set of raw meteorological data produced by sophisticated computer models. The forecasting models are getting better and better, but GRIBs should be treated with caution. My personal experience is that the GPS model is very accurate for three days, especially away from large land masses.
WIND, WAVES &RAIN
The most common GRIB model used is GFS, which is produced by the United States' National Weather Service. It’s normally very accurate for three days and the decreases in its accuracy for longer forecasts.
Another model claimed to be better for medium range forecasting is the ECMWF (European Centre for Medium-Range Weather Forecasts) model. This data has to be bought on a subscription, but several weather websites display it for free e.g. Windytv and PredictWind. (See our Weather Forecast Websites page)
OCEAN CURRENTS
There are two main models for Ocean Currents: RTOFS and OSCAR.
1. RTOFS is produced by the US NOAA service and gives worldwide coverage of current forecasts for up to seven days ahead. It is available via SailDocs.
2. OSCAR is produced by US NASA and is available by email from www.svsarana.com/oscar/
There’s an interesting article on obtaining Ocean Current data by David Burch. http://davidburchnavigation.blogspot.my/2013/02/obtaining-ocean-current-data-underway.html
OBTAINING GRIBS
Standard GRIB Files
The easiest way of obtaining GRIB files is to send a request email to “query (at) saildocs.com”. This is a free service and their automated email system will send you the GRIB file(s) as an attachment.
You can send an email to This email address is being protected from spambots. You need JavaScript enabled to view it. to get detailed information about their service, which also included weather faxes and satellite images.
Here is a typical request for two GRIB files for the area between Phuket and the Andaman Islands - GFS wind, pressure & rain, and the RTOFS ocean currents. The GFS data is available as a 14 day forecast, but the RTOFS data is only a 5 day forecast.
To: query (at) saildocs.com
Subject: Anything that you want (Phuket to Andamans)
GFS:5N,15N,90E>100E|2.5,2.5|0,6..384|WIND,PRMSL,WAVES,RAIN
RTOFS:3N,12N,75E>100E|1,1|0,6..192|CURRENT
Note that the body should only contain the two lines (turn off or delete any automated signature). Also the format is very fussy, in particular, remove all spaces from between characters on each.
For the above example, within a few minutes, you will receive back two emails, each with a grib file attached. Uncompressed they are 26K and 4K in size. Save the attachments in a GRIB folder with significant names, (such as “2016-12-21 Phuket to Andamans”), then open the gribs in your favourite GRIB viewer.
Oscar Current Data
The easiest way of obtaining OSCAR data is to use the facility set up on the svsarana web site and send an email to their automated server.
To: query (at) svsarana.com
Subject: Anything that you want (Phuket to Andamans)
oscar:3N,12N,75E,100E