NEW YORK (TheStreet) -- The surprise move by the Chinese central bank to devalue its currency is having a big negative impact on the equity markets today, but the impact could be far more reaching than a mere day of volatility, offering both upside potential and risks.

As of late, investors have been bracing for the U.S. Federal Reserve to raise interest rates in September. While that date is hardly official -- other estimates range from December to early 2016 -- the probability of it coming sooner rather than later has risen. Last week's payroll report showed enough strength as to suggest the Fed could move next month, and recent comments from Fed officials also pointed in that direction.

China's move changes the equation. The Fed has said it would begin hiking rates as soon as it deems the economy strong enough to withstand such an action, and the devaluation of the yuan, which should correspond with strength in the U.S. dollar, raises new questions about what economic growth will look like from here. A stronger U.S. dollar will have a negative impact on revenue growth going forward, and profits at big multinationals -- the bellwethers of the overall economy -- could be eroded by currency headwinds. That could lead to overall economic growth in 2015 coming in under 2%, hardly the kind of environment that seems fully capable of absorbing higher rates.

Furthermore, the move is putting new pressure on oil prices, which have already been decimated this year. On one hand, that's good news for consumers, who stand to save money at the pump, but on the other hand, it means rig counts will continue to fall, and that means additional layoffs in the energy sector are almost guaranteed. And of course, the mere fact that China felt this step necessary screams weakness, and slowing there will hit U.S. companies with heavy exposure to the region -- a list that ranges from Yum Brands(YUM) - Get Report to Apple(AAPL) - Get Report .

What this means is, even if the Fed wants to institute its first rate hike in about a decade, it may not be able to. The result of that for the U.S. equity market is uncertain. Some names could rally on the hope of a few more months of low rates -- Wall Street's broad rally over the past few years has come in large part on the Fed's rate policies -- but a few more months with rates at record lows may not be enough to generate meaningful upside from here. One thing that does seem certain is that volatility is likely to rise.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.