Powell will speak at a symposium in Jackson Hole on August 26 at 6 p.m.

The Fed chief is expected to signal for continued rate hikes, but the question of "how aggressively" will remain open, Bloomberg reports.

According to another poll, the Fed will raise the federal funds rate by 50 bps in September, 76 of 94 economists believe, while 18 think it will increase by 75 bps.