Weather

Note we do not have any financial arrangements or other interests in any the products mentioned here!

For just about every question, there are almost as many different opinions as there are sailors. And, most of these different opinions are in fact valid for the specific individual with their particular boat and their unique mission.  That said, below are our opinions based on our experiences to date.  We reserve the right to change them, or even admit they are wrong, at any later date :)

1. Have you been in many storms?

10. What sort of weather tools do you use?

43. Another crew seems to be getting 'better GRIBS.' What are they doing?

61. How do I pick where to cross the doldrums?

Also see:

Weather revisited - 2001, SAIL

Weather - when to reef - 2001 SAIL

Getting GRIBs - Cruising World 2007

1. Have you been in many storms?

We have never been in hurricane force winds at sea.  We have only seen over 60 knots sustained (12 sec averaging) once, approaching Cape Horn.  We do encounter about a day or two per year of storm force winds on average (closer to 1 day/month in the Southern Ocean).  Contrast that with the fact that we spend about 30% of our time offshore in winds under 10 knots. The real challenge offshore is not storms, but trying to keep the sails full and the boat moving in day after day of light winds and calms.  Top of Page

10. What sort of weather tools do you use?

First, and most importantly, we look outside at the sky and at the barograph and make our own prediction, which is often more accurate than the official forecast.  This takes practice, but it is something you can start working on before you even buy a boat. Chapter 19, Weather Basics and Onboard Forecasting, in The Voyager's Handbook will get you started.

GRIBs are now our primary source of external weather information at sea.  Weather fax was our main weather source on Silk, but GRIBs have basically replaced them. The GRIBs are reasonably accurate (as accurate as the custom service professional weather routers we have worked with) in latitudes higher than 25°.  Nearer the equator they are not as good and weather faxes that identify tropical waves and convergence zones can be better.  We get GRIBs from Saildocs via an Iridium phone (most cruisers use an SSB and Pactor modem) onto our laptop running a free program called Viewfax.  We can get weather faxes from our Sony all band radio via an audio cable to our laptop microphone jack through a program called Weather fax 2000.   

We listen to various weather nets on SSB frequencies and love it when we have a boat about 200 miles to the west of us reporting their weather on a net, as that usually gives us a good idea of what's coming. 

We do have an Inmarsat C system, which gives us free text weather (Navtext) twice a day, in addition to limited e-mail and emergency signalling capability.  We like the Sat C system but it is almost obsolete with few suppliers still in business.  You can now get the same text forecasts from Saildocs (either via SSB or Iridium).  We are currently looking at getting a BEGAN system, which has operating costs similar to Iridium but with 10 times the data speeds.  Land-mobile BEGAN systems have been available for about a year but the current marine sets are well out of our price range ($13,000). If/when the price comes down, we will consider replacing our Inmarsat-C with BEGAN. 

We have used professional weather routers on several of our longer and more difficult passages but found they did not add much value.  Top of Page

43. Another crew seems to be getting 'better GRIBS.' What are they doing?

GRIB files (short for gridded binary files) is a generic term for a file compression format specifically designed to efficiently send weather data to low bandwidth receivers (high frequency radios or satellite phones).  The GRIB file format can encode a wide range of  weather data including surface winds, surface barometric pressure, 500mb (upper level) winds, 500mb temperature, ocean currents, water temperature, wave heights, rain fall, and sea ice density.  The GRIB data can be obtained from many different sources (mostly government meteorological services but also some private services) and many different computer weather models. 

When most sailors say they have gotten a GRIB file, they have gotten it from NOAA's (US government meteorological service) "GFS" global model.  This is a very sophisticated computer global weather model that the US government provides free to all.  GFS data is generally available on a 0.5 x 0.5-deg grid every 3 hours out to 180 hours, and then on a 2.5-deg grid out to 384 hours (16 days). Available parameters are surface pressure, surface winds, 500mb winds, 500mb height, air temperature and sea temperature.

If you see another sailor getting what looks like a ‘better GRIB,’ it is most likely from the same GFS model but at higher resolution.  The default settings return 2 degree by 2 degree resolution, but it is possible to request data resolution up to .5 degree by .5 degree which provides much more accurate detail especially around coastal features.

Alternatively, the other sailor may be accessing a different model entirely. For reference, models used by the most popular GRIB servers: Ocens and Saildoc’s default GRIB source is GFS; the French MaxSea uses Wave Watch 3 (WW3); and the GMN GRIB robot also uses WW3. 

WW3 is NOAA's wave model.  Data is available on a 1 x 1.25 grid (lat x lon), forecasts every 3 hours out to 180, updated every 6 hours. The primary parameter is height of significant waves, with other parameters like wind speed calculated from that.  Generally GFS is preferred to WW3.

If the ‘better GRIB’ is not from GFS or WW3 then it is most likely a ‘mesoscale’ (e.g. regional) model. Current global models like GFS do a very good job over open water, but are less accurate near land. An alternative is to take the data from the global model, and use it as input to a regional model on a finer mesh with more detailed modeling of land effects. One such effort is the US Navy's COAMPS ("Coupled Ocean/Atmospheric Mesoscale Prediction System") model. Forecast data is available on a 0.2 x 0.2-degree grid at 6-hour intervals out to 48 hours (72 for west-Atlantic). Surface pressure and winds are available.

The currently modeled COAMPS areas are:

East-Pacific:  29N to 60N,160W to 114W

West-Altantic: 20N to 55N,093W to 055W

Cent-Am and Carib: 00N to 32N,120W to 060W

Continental US: 24N to 50N,126W to 066W

The availability of regional models is an exciting development as it has the promise of providing better predictions of inshore weather. Recent comparison of GFS with COAMPS suggests that COAMPS is preferred within about 20 miles of shore and beyond that GFS is better.

Two other GRIB models are also sometimes accessed by sailors:

"Nogaps" is a US Navy model and data is available on a 1-deg grid with forecasts every 3 hours to 24, then 6 hours to 96, then 12 hours to 144, and updated every 12 hours. Available parameters are surface pressure, surface winds and 500mb height. The server is sometimes late which results in missing valid-times.

Quickscat (Qscat) data is real time wind data which is calculated from wind-wave radar observations made by polar-orbiting satellites. This is now available in a gridded format. Qscat data is updated whenever NOAA updates the dataset, generally once per hour although sometimes a few hours elapse between updates. The data also includes layers for the age of each data-point (typically 2-24 hours) and a rain status flag (rain can corrupt the data). Quickscat data is used (along with traditional observations) to initialize the GFS model.

There do not appear to be any high resolution GRIBs available for the Beagle, Antarctic, S. Georgia area.

All the above GRIB models are available (for free) from SailDocs.

Many weather services run global or regional models but unfortunately most governments have not followed the US lead in making data produced with public funds available to the public. Both the British and French government meteorological services have computer models generating GRIB data, primarily designed to provide more accuracy than the general global models in coastal waters. The French also generate data for their overseas departaments and territories. This data is available through several fee-based plans from Meteo-France. Top of Page

61. How do I pick where to cross the doldrums?

Historically sailors have picked their crossing point based on the seasonal pilot charts and amassed experience of past sailors. This information was codified in the British "Ocean Passages of the World" and has been continued in Jimmy Cornell's "World Cruising Routes" (one of two books all Blue Water cruising boats should have on board).  This method works pretty well but was developed before sailors could get near real time weather information on board. You can use modern weather information to make an even better crossing but it's not completely straightforward (even for the shore base weather routers who twice gave us poor crossing points before we stopped using them).

If you look at the normal gribs (This is a grib with Wind arrows and Isobars - the doldrums start at about 4-6N around here)), you will not even see the doldrums. If your grib view can view layers (as Viewfax can) then you can ask for a rain layer and then you can see the doldrums in the grey rain layer (the same grib with a rain layer shown) Then the question is where do you cross?  There seem to be two different opinions: (1) is to pick the narrowest band of rain, figuring this to be the shortest point of the doldrums, (2) is to pick the heaviest area of rain, figuring this to have the strongest wind associated with the rain squalls.  Obviously if you could find a narrow point with heavy rain that might combine both aspects.  Our sense is that the racers go with approach (2) and cruisers with (1).

I asked our friend Stan Honey (Winning Volvo Navigator) what his approach was.  His answer was:

"Typically the best answer is to pick your doldrum crossing using the climatological data, as it sounds like you normally do. If you can't motor and therefore want to try to minimize the amount of dead calm in your doldrum crossing, then you can watch the satellite photos and look for the batches of turbulence and convection that come off of the African desert. They move W along the ITCZ.  If you cross the doldrums passing under one of those patches of turbulent convection, then you will get plenty of clouds and squalls to work with to help you sail through the calm part of the doldrums.

You can easily see the patches of convection and turbulence on the sat pictures as cloudy patches, sometimes V shaped with the tip of the V pointing W. If you can motor in the dead calms, then I wouldn't worry about trying to fine-adjust your crossing. As usual, when you actually get to the light air, use every opportunity (i.e. every cloud and squall) to get North to minimize your time in the light stuff. In no event would you want to get within 75 miles of the coast of South America. The trades stop in there. Once you're in the NE trades then resume course for Antigua or wherever.

It will be a struggle to get sat pictures from the internet via Iridium but the patches with lots of convection will be visible in the sat images that you can get on HFFAX from New Orleans. They are not usually detectable in the grib files because they are not a synoptic feature. Sometimes a meteorologist will indicate them on the surface charts. It varies."  (Top of Page)

 

"Suddenly, you have realized how fragile your beliefs were. Those that used to be your pillars are now only faint thoughts. The Almighty has played the old joke of taking away the chair on which you were going to sit every day. You have hurt yourself, you have felt pain, and this is also good. If you had fallen down over something soft, you would not have paid attention to it. But the truth is that you have landed on another reality. You are bewildered, your consciousness flustered. You do not understand anything of what has happened. You feel like you have wasted your time until now, and you may even feel shame for what you did before. Retrospectively, you will see yourself as somebody dedicated to futile things.

The pain blinds. Even if you do not understand it, know that what has happened to you is something marvelous. You are no longer the same as you were moments ago and, if you are wise enough, you will never be. Other things will matter now, you will climb other mountains. You will face other demons, other brothers will walk along with you. Live your new life, look with new eyes. Nevertheless, be prepared to be reborn. Again. Only by doing so will you be able to reach the end of the way."

L.E. Schultz