A weakened dollar and still-brisk growth in the emerging world will keep exports growing, so altering the orientation of the economy from domestic consumption to tradable goods.

Speaking from the function orientation of the Fed, it's responsible for the economic growth of the U.S., job creation, and the maintenance of domestic low inflation rate.

This re-orientation of demand growth away from the US, and associated shifts in interest-rate expectations, are resulting in a weaker dollar.