Winddirection: Rotated LatLonGrid

[Ronny Meyer]

Hi, I am looking for a solution or a GRADS-script for the following problem:

I have the windspeed and winddirection in a rotated LatLon grid and I
want to compute the windspeed and winddirection in the geographical grid.
I think, that the windspeed (as a skalar) must be the same in both
grids, but what is with the winddirection?
It is clear that I can determine the new angle by calculating the u- and
v-component in the rotated grid and do the rotation backwards and
calculate then the winddirection.
But: Is there an easier way to calculate it, without knowing the u and
v-component?

Thanks for any hints

Ronny