Federal Reserve Chair Jerome Powell faces a communication challenge in the coming week as he leans toward paring back stimulus while trying to avert speculation that such a shift presages future interest-rate increases. Fed officials are expected to signal a start to scaling down monthly bond purchases in their policy statement at 2 p.m. Washington time on Wednesday, the most significant among at least 15 global central bank decisions due. Economists surveyed by Bloomberg see that hint being followed by a formal announcement in November.