I was flying at the weekend from the south of Spain back to the uk. In the descent we had a head wind of 180 kts between fl360 and fl320. The last time I saw a wind approaching that was over the Arabian gulf. If the aircraft have a normal TAS of say 440kts then all of a sudden you're cruising at less than 300kts ground speed. That will ruin your day on a trams Atlantic crossing.