This is not how interpolation is implemented in Vrtool I'm affraid.
Using U / V components interpolation is a poor choice for wind speeds,
as is explained in this page:http://gfesuite.noaa.gov/publications/p ... Paper.html
I used the method described in the page below (in uGrib site):http://www.grib.us/Forum/tabid/55/forum ... fault.aspx
It seems to me odd to use wind magnitude to interpolate wind speed
while using U/V components to interpolate direction. VRTool interpolates
both speed and direction using TWS/TWD pairs.
how much this difference is significant remains to be checked.
p.s. Volvo 14 prelude polars basic