Traveling 20 hours due east at 30 kilometers per hour, the ship sailed 20*30=<<20*30=600>>600 kilometers the first day.
If half the distance to the destination is 600 kilometers, then 2*600=<<2*600=1200>>1200 kilometers is the total distance from start to destination.
One-third of the distance from start to destination is 1/3 * 1200 = <<1200/3=400>>400 kilometers.
Thus, the wind storm blew the ship in a westward direction for 600 - 400 = <<600-400=200>>200 kilometers.
#### 200