People work at the Halfaya oilfield in Amara, southeast of Baghdad, Iraq. Essam Al-Sudani | Reuters

Oil prices are heading for a downturn later this year and will sink even lower in 2019 as the fundamentals of supply and demand weaken, J.P. Morgan forecast in a research note on Friday. "While geopolitical tensions and lingering risks of large supply disruptions remain an upside risk throughout 2H18, we think that prices will be corrected downwards towards end of the year and remain capped in 2019," J.P. Morgan analyst Abhishek Deshpande wrote in the note. Despite oil prices recently rising to 3½-year highs, the investment bank left its forecast for international benchmark unchanged at $69.30 a barrel. On Friday, Brent was trading at just under $77 a barrel, off its recent high of $80.50. J.P. Morgan now sees U.S. West Texas Intermediate crude averaging $62.20 a barrel, down $3 from its last estimate. WTI was trading at nearly $66 a barrel Friday, after nearly touching $73 a barrel two weeks ago. The bank knocked down its 2019 Brent forecast by $1, to $63 a barrel. It lowered its outlook for WTI slightly to $58.25 a barrel.

An OPEC meeting in two weeks will determine the short-term price movement, the bank says. Oil market heavyweights Russia and Saudi Arabia have recently signaled they could ease a deal between the 14-member OPEC and other producers to limit output, which has been in place since January 2017. The Saudis and Russia are wary of prices rising high enough to dent demand as Venezuela's output continues to decline amid an economic crisis and as U.S. sanctions come into force against Iran, OPEC's third-biggest producer. Oil prices suggest the market is betting on an output increase of about 400,000 barrels a day, according to J.P. Morgan. "We think there might be one last hurrah (upside) when it comes to prices especially if OPEC were to announce a release of barrels which is less than what markets have priced in currently," Deshpande said. Still, J.P. Morgan thinks the rally would unwind. That's because any move by OPEC to ease output caps would signal a return to pre-2017 production levels. It would also tip the finely balanced oil market towards oversupply starting in the fourth quarter, when the restored barrels are likely to start arriving at import terminals. J.P. Morgan already believes the supply-and-demand fundamentals of the market are poised to weaken.