Like a field judge in the Olympic track and field events, Fed Chairwoman Janet Yellen may use her speech in Jackson Hole to start the race for a rate hike as soon as September.

Yellen will speak Friday from the Fed’s summer retreat at 10 a.m. Eastern. The subject of her remarks is “The Federal Reserve’s Monetary Policy Toolkit.”

“We see Jackson Hole as the ‘ready’ warning and look for Chair Yellen to err on looking at the optimistic side” of the outlook,” said Drew Matus, senior U.S. economist at UBS.

To be fair, Matus thinks the U.S. central bank won’t issue the “set” warning until its September meeting policy statement and then “go” at the December meeting.

But many economists think the central bank could “go” in September if the jobs data is strong.

The Labor Department has reported two strong months of employment gains — 255,000 for July and 292,000 for June.

“If the August employment report, scheduled for release on Sept. 2, is solid, then we expect the Fed to raise rates at its September meeting,” said Michael Gapen, chief U.S. economist at Barclays.

“We expect Yellen to deliver a stronger signal about the likelihood of near-term rate hike” at the Jackson Hole meeting, he added.

“Another solid employment report would go a long way in building the case for a September rate hike,” said Michael Gregory, deputy chief economist at BMO Capital Markets.

If that is not enough, Yellen could make it clear “how much more rate-hike-corroborating data she has to have in hand before raising rates again,” he said.

Market participants see the chances of a rate hike this year at 50-50.

About 71% of 62 economists surveyed by the Wall Street Journal earlier this month said the Fed will wait for its Dec. 13-14 meeting.

“With only a chance a 20% chance of a move being priced in for September, an uncertain FOMC and no real catalyst to prompt a move in September, December remains the most likely timeframe for a (too) cautious Fed, in our view,” Matus said.

Financial conditions are already being squezed by an unexpected rise in money-market rates.

Read: Investors wary of current rise in Libor

Supporters of a September move think the outlook changed given that two of Yellen’s close allies on the U.S. central bank — San Francisco Fed President John Williams and New York Fed President William Dudley — have raised the possibility of a rate hike at the September meeting.

Also read:Fed’s Dudley says September rate hike ‘is possible’

“Since Williams and Dudley are both intellectually aligned with Chair Yellen, we expect her speech to retain the optionality of raising rates in September if economic and financial conditions permit,” said Joseph LaVorgna, chief U.S. economist for Deutsche Bank.

Any inkling of imminent Fed tightening should make the dollar stronger and move the U.S. yield curve higher relative to other markets, said Carl Weinberg, chief economist at High Frequency Economics.

What would motivate a rate hike in September?

Kevin Logan, chief economist at HSBC, thinks the Yellen’s message could be that the “fog is lifting” and the central bank is closer to its goals of full employment and stable 2% inflation.

Robert Brusca, chief economist at FAO Economics, said the Fed has a desire to move rates higher to counter suggestions that their first move last December was a mistake.

“The longer they go without following up on the December rate hike makes them even more vulnerable to the charge that the move as a mistake,” he said.