Business cycle phasing (US hits bottom first and presumably recovers first while rest of world lags), or anticipation thereof would tend to lead to dollar strength at what intuitively should be a weak point in time.

The dollar simply sucks less than the currencies it is being compared to (e.g.Euro). The U.S. is much further along in this down cycle/recession than the rest of the World (which until a few months ago was assumed by many to be “decoupled”).