US stocks open higher ahead of Yellen speech

US stocks headed modestly higher in opening trade Friday as markets awaited a speech by Federal Reserve Chair Janet Yellen that could shed light on plans to hike interest rates.

Caution reigned ahead of the speech at the Fed's central banking symposium in Jackson Hole, Wyoming, scheduled for 1400 GMT.

"The market has been consumed with that speech and won't show any conviction until it sees that speech," said Patrick O'Hare of Briefing.com.

Five minutes into trade, the Dow Jones Industrial Average was up 0.3 percent at 18,498.88.

The broad-based S&P 500 added 0.3 percent at 2,179.75, while the tech-rich Nasdaq Composite rose 0.3 percent to 5,227.32.

Yellen's speech aside, there was little hard news to send traders in one direction or another. As expected, the official estimate for US economic growth in the second quarter was revised slightly downward to 1.1 percent.

Early estimates for US goods trade in July showed a narrowing of the deficit, which would boost third-quarter growth.