We have been under sail for one week now! We hope to reach our landfall in another two weeks or a little more. It looks like the weather is shaping up for us to get around the high. In fact, the high is predicted to step aside in a couple of days to let us pass!
How do I get that kind of information way out here on the ocean? Every day, I download data files generated by NOAA's Global Forecasting System (GFS) as an attachment to a Sailmail email. These are great, and they are free. This type of file is called a grib (gridded information base) because it consists of tuples of data for each point in a grid. I specify the grid by giving the latitudes and longitudes of its four boundary corners and how close within this region the points should be. I also specify which data items should be included in the tuples and the frequency of predictions. I ask for wind speed, wind direction and barometric pressure for ten days. A website called Saildocs.com, which is related to Sailmail, allows me to set up my grib request as a subscription. Each day, Saildocs downloads my grib from NOAA, attaches it to an email addressed to me, and sends it to my Sailmail account. The next time I am able to connect to Sailmail, it is automatically downloaded. Because due to the vagaries of HF radio propagation I am only succeeding in connecting to Sailmail in the evening, that is when my grib arrives.
(Incidentally, gentle reader, even if you are not a sailor you can use Saildocs. Information on their website explains everything you need to know to get your own gribs or many other interesting reports, on either a one-time or subscription basis.)
Once I have my daily grib, I open it on my laptop with a program called zygrib, which is an example of a "grib viewer." Zygrib displays the data as geographical images that very much resemble weather maps, one for each prediction time or, in our case, one for each day. I can easily move backwards and forwards through the predictions for the next several days. The only thing that zygrib images lack that the surface predictions drawn by the weather specialists at the National Weather Service possess is any indication of warm and cold fronts. Highs and lows are handled quite well. Since I am now concerned primarily with the location of the Eastern Pacific High, fronts are irrelevant. Once we get up to the zone of the westerlies, low pressure systems will become more interesting and then I will try to use the fax capability of my radio system to get surface forecasts as traditional radio-fax images.
At UTC 2200, July 19, 2012, we are at 35 19.471 N, 160 00.034 W. Our day's run was 115 miles.
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