The main question is how prepared emerging market central banks are for a Fed rate hike and how much the Fed actually ends up hiking beyond the first quarter-point rise. Top Fed officials have insisted that rate hikes will be gradual and shallow. Fed Vice Chair Stanley Fischer recently said that emerging market central bankers have been telling the Fed to "just do it," which suggested to him that they were prepared for a rate hike. He has said previously that those countries that have not dealt with their budget deficits and have large external debts, that is, in foreign currencies, could be among those hardest hit by a Fed rate hike.
This won't be the first time the Fed has acted before other major central banks. It cut rates in January 2001, five months before the newly born European Central Bank. The Fed hiked in June 2004 (the last time the Fed raised rates), 18 months before the ECB would move. And it cut again in September 2007, 11 months before the ECB, which actually flirted with raising rates once during the period.
The history shows that the big global central banks often are not synchronized but they do appear to move in the same general direction over the medium term when a Fed rate hike eventually leads to the Europeans' and the Brits' following suit. Japan, which has its own, unique problems with deflation, is less predictable, but it did join the Fed and the ECB in hiking in 2005 and in increasing bond purchases in the wake of the financial crisis.