Cochilco also lowered its 2019 price projection to $3.05 per pound from the $3.10 it predicted in July, saying there would be a continued depression in demand for the metal because of US-China trade tensions.
It said it expected the price to rise to $3.08 in 2020.
Cochilco's head of studies, Victor Garay, said the metal price for the last two months of the year would continue to trade around recent values, albeit amid significant volatility.
The copper commission projected output of 5.76 million tonnes from Chile, the world's top producer, for this year, an increase of 4.7 percent from the previous year, because of a long-running copper strike in 2017 that blighted production.
It predicted further rises in Chilean production of 3.1 percent and 1.4 percent in 2019 and 2020, respectively.
Cochilco said global demand for refined copper would edge up 1.3 percent this year, and 2.3 percent next year, with lower global production resulting in a slight deficit.
Pablo Terrazas, a Chilean mining minister, said the market fundamentals remained solid.
"The supply and demand situation points to a consolidation of a projected deficit in the metal for the 2018 - 2020 period, albeit at limited levels," he said.