The lateral effect of wind isn't a linear calculation (I was told "think Pythagoras"). I've copied this from someone (my apologies I forget who so cannot give credit). Basically if the wind is blowing at 45˚ the second line is the amount you offset, this works pretty well at all distances.
I don't know what math was used for this as, as I said I've copied this from elsewhere but from my experience it is pretty accurate. Of course if the wind isn't at 45˚ you have to adjust somewhat.
Normal
0
false
false
false
EN-GB
ZH-CN
X-NONE
Crosswind
strengths
Wind strength at 45 degrees:
10 12 14
17 20 23 24 26
27 30 33 38 41 42
The cross wind component:(Mph)
07 09 10
12 14 16 17 18
19 21 23 27 29 30