Grib Files
18 February 2008 | Luperon Dominican Republic
Capt Chris
For old salts who may be saturated in all things weather, sorry for boring you with the graphic. But for people who are just learning, cruisers spend a significant time looking at the "grib files."
Their are many sources to find grib files. This particular one was pulled from passageweather.com. Grib files are created by pulling data from computer programs (weather models) and then the programs extrapolate out 180 hours or so from the moment the model is "run." NOAA has a couple of good models, the Brits have another and the U.S. Navy also has a reliable forecast model. Forecasters use these same files as a piece of the weather puzzle. Weatherman over a period of time can compensate for inaccuracies of each model as each model will tend to over or under forecast in certain situations. Between all the models they come up with a text forecast. Us sailors love to second guess them and of course bash them relentlessly when they are wrong. We seem to think we have a handle on everything because now we have access to the raw data, just like them. Truth is forecasting the weather beyond 48 hours in most circumstanes is futile. But it still is very important in my view to study the weather patterns on a large scale because the term accuracy can be a loose term when it comes to weather. For example. Here on the north coast of Hispanola, for me the difference between 10-15 knots during the day and 15 to 20 knots during the day is the difference between a decent passage and pure hell. So for a forecaster it can be very difficult to predict that 5 knot difference on a micro scale. But on a macro scale you can start to sense from the data when those types of condition may assert. Or you can easily tell if a large north swell is heading south in which case it doesn't matter what the wind is, it would be a no go.
Ok, so in this particular graphic you can see that the weather model is forecasted out to what the predicted surface winds and direction will be at 132 hours (from when the model was initiated) and you can see the date and time. Time is always UTC and for me that is five hours ahead. So this is what the wind should be at 7pm this coming Sat. Now you can easily see in the upper right hand corner the edge of the Atlantic High as the winds are light and variable near its edge. Look toward the west and east coast of Florida and you can see the wind is light and starting to bend south. This tells us that a cold front is passing through Florida and on its way to the Bahamas. This is the type of conditions we here in Luperon watch closely as they are the precusor for a potential weather window.
With all that said, we have a potential window developing Tues, Weds and Thurs of this week. Today and tomorrow will be filled with weather analysis and boat prep for a possible move 125 east to the Samana. This would be the staging point to cross the Mona Passage to the West coast of Puerto Rico where I will clear Customs. So we shall see. Another 8 boats arrived yesterday from Turks and Caicos, so the harbor is jammed with boats and activity. If I don't make it out of Luperon this week there is always next week. I am enjoying my time here very much. If I stay another week a few of us are thinking about heading to Haiti for the day. But all this is speculation!
Capt Chris