June 16 (Reuters) - Morgan Stanley has lowered its Brent crude oil price forecast for the fourth quarter of this year by $15 per barrel to $80, after the U.S. and Iran signed a preliminary agreement to end the war in the Gulf.

"From here, it likely takes several weeks for tanker flow to be restored; we see 50% of production back by September, and 80% by December, slightly faster than before," the bank said in a note dated late on Monday.