U.S. stocks open higher ahead of Fed chair's speech

U.S. stocks opened higher on Friday, as investors anticipated a key speech from U.S. Federal Reserve's Chair Janet Yellen.

Traders kept a close eye on Yellen's speech for more clues on the timing of the next interest rate hike. She is scheduled to deliver a speech later on Friday morning on the U.S. economy and monetary policy at the Economic Policy Symposium at Jackson Hole, Wyoming.

Some Fed officials' hawkish comments have strengthened market expectations that the central bank might raise interest rates later this year.

"If Janet Yellen sticks strictly to her topic 'Designing Resilient Monetary Policy Frameworks for the Future,' many will be disappointed," said Stephen Guilfoyle, chief market economist at Stuart Frankel & Co., on Friday.

On the economic front, the U.S. real gross domestic product (GDP) increased at an annual rate of 1.1 percent in the second quarter of 2016, according to the "second" estimate released by the Commerce Department Friday. In the first quarter, real GDP increased 0.8 percent.

Shortly after the opening bell, the Dow Jones Industrial Average gained 66.25 points, or 0.36 percent, to 18,514.66. The S&P 500 rose 8.02 points, or 0.37 percent, to 2,180.49. The Nasdaq Composite Index increased 17.38 points, or 0.33 percent, to 5,229.59.

U.S. stocks wavered and closed lower on Thursday, as investors digested a batch of newly released economic reports. Endi