Two step weather routing

Two-step weather routing with VRTool

Suppose you want to plan a route with an intermediary point. Say it is not a fixed point like a mark or an island, but a strategic position, close to favorable winds. You don't know where it is yet, but you feel it is in a certain direction where winds are normally stronger and/or in a suitable direction.

VRTool WR calculator can only work a single segment at a time, from Start to Destination. However you can create a composite route by doing as follow:

Set WR destination far away in the direction you like and do a WR calculation. Plot only the isochrones to the chart. Use the isochrones to choose your strategic intermediary position.

Say you choose a position on the 108h isochrone. Set WR destination to that point and do a calculation up to 108h. Plot the best route. This is the first part of the track.

Now you can do the second step, from that position to the final destination. The second segment will start from 108h. Set WR Start to your chosen 108h position and Destination to the leg final destination.

In the program's main window, in "Track Designer Settings", "Wind Forecast Age" group, select option "a given date/time".

Now you have to figure the date/time of the 108h isochrone. Go to the "Wind grids" and select the current wind grid. The Timestamp will show below.

Add 108 hours to the timestamp and convert back to date/time. This time is in UTC. Convert to local time by adding the time zone. Input the date/time to the "Start" field in track designer settings. Then you can calculate the second part of the WR track. The calculation will start with 108h winds. Plot the best track.

Remember to set "Wind Forecast Age" back to "windgrid timestamp + a time zone" in the end (the default mode).