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4/08/2020 5:02 am  #1


Best practice for routing beyond available weather?

Normally I use expedition to route courses of 350 nm or less, typically each leg of the course can be routed from start to finish with the weather data at hand (5 days or so).

Now I’m routing for a friend that must do a 12 000 miles solo non-stop sail from the Maldives in the Indian Ocean back to Sweden due to Corona restrictions.

First leg Maldives – South Africa, is already far beyond available weather data. What is best practice when routing such a long leg?

Any thoughts general on long distance routing or specific to sailing Maldives – South Africa - North of Scotland and back to Sweden would be greatly appreciated!

Also, if anyone has recommendations on more or less accurate weather models or current models for the different parts of the sail, it will help a lot. It is all far away from my, in comparison tiny, racecourses in the Baltic.

 

4/08/2020 12:24 pm  #2


Re: Best practice for routing beyond available weather?

You can get GFS from Saildocs out to 16 days. Of course, it gets marginally useful that far into the future.

The Expedition weather server only goes to 10 days for this reason.

In practice, the solution is to have an idea of the area of the ocean you want to be in at any point. In big ocean races, we do historical routing studies for this, with (eg) GFS or ECMWF reanalysis data.

With currents, you can tell Expedition to use the last data available. This an be a valid choice as oceanic currents change relatively slowly. You can also do this with the wind, although it is less likely to be an ideal choice.

 

4/08/2020 1:11 pm  #3


Re: Best practice for routing beyond available weather?

Fredrick,
Dare I mention low tech Pilot Charts?  Readily available free on the web e.g.  www.kp44.org

Also you might help your friend with planning which routes have 'security' issues i.e. piracy and any issues like shoals that only show up when 'zoomed in'. Also great circle routes for shortest distance etc

All these things could be a huge help for planning a route well in advance especially for a solo sailor.
Good Luck,
Ernie

 

4/09/2020 11:53 pm  #4


Re: Best practice for routing beyond available weather?

Fredrik, agree with Nick and Ernie.  16 days out (GFS), the forecast is pretty nominal and routing off it chancy at best.  That means using seasonal climatic averages is a better choice - this is where Ernie's recommendation of Pilot Charts is important.  You can't know the exact weather, but you can kniw the averages and the seasonal risks.  To me always a good idea with an ocean passage in unfamiliar waters.

 

4/10/2020 1:59 am  #5


Re: Best practice for routing beyond available weather?

As Nick mentions, a very good solution for this is to optimise the route using historical reanalysis data from either GFS or ECMWF. Using the Multiple route feature in Expedition over many years for the specific departure point and date would paint you a pretty interesting picture of the potential weather for the route.


:::Campbell Field::::::www.fieldyachting.com:::
 

4/12/2020 2:28 pm  #6


Re: Best practice for routing beyond available weather?

Nick -- any chance getting an expedition feature to pull down the reanalysis gribs the same as current weather?

 

4/12/2020 5:15 pm  #7


Re: Best practice for routing beyond available weather?

Campbell_Field wrote:

As Nick mentions, a very good solution for this is to optimise the route using historical reanalysis data from either GFS or ECMWF. Using the Multiple route feature in Expedition over many years for the specific departure point and date would paint you a pretty interesting picture of the potential weather for the route.

this is the best way - it's fairly easy to get 5-10 years of reanalysis and run 100's of routings using the "multiple" option.

doing some work for the now-cancelled bermuda race, i got 10 years of june reanalysis, and ran 1 route a day, for the 2 week period centered on the start date.., for 10 years - so 140 races.

the expedition filter output then goes into excel.., and from there you do what you want with the data

of course, the bermuda race is not really a situation like that of the OP, as the forecast s often pretty good for the ~3-4 days of the race..

i did a similar thing preparing for a trade-wind transat delivery i did last march - and that is typically longer than one can count on the forecast to be good for.

i have been playing a lot with the route data in excel, and i'm not really thinking i have yet hit upon the best way to analyze the data.., a way that makes full use of it.., especially when i have the wave spectra data.

 

Last edited by us7070 (4/12/2020 5:16 pm)

 

4/15/2020 12:45 pm  #8


Re: Best practice for routing beyond available weather?

Thanks all for good help,historic data sounds like a very good solution, does anyone know where I can find historic GRIB files?
 

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