The competition to complete the semi-final list will now be held on Monday.
The competition web site said the problem was "dynamic and fast-moving conditions...ushering in significant rain showers and the ever-present threat of thunderstorms coming off the hills."
It said the race director Iain Murray decided in the afternoon to cancel competition for the day because of "the risk of lightning".
The final day is crucial for the French Orient Express team. They sit last in the standings with one win and six losses and must win against Ineos Britannia, whose record is 5-2.
A victory for the French would pile the pressure on the Swiss Alinghi Red Bull Racing team, who are 2-5, and would need a win against table-topping Italians Luna Rossa (6-1) to avoid a winner-takes-all race-off with the French for a semi-final berth.
The weather delay may have helped the French who damaged their yacht in morning practice. They returned to port suffering unspecified structural problems. Their shore team made repairs just in time for the boat to be fast-towed out to the start line for their scheduled race against Ineos Britannia. Then the weather intervened, giving the French more time to work on the boat.
Luna Rossa suffered their first defeat on Saturday to Ben Ainslie's Britannia team. Both Britannia and Luna Rossa are already assured of advancing to the semi-finals.
American Magic are third on 4-4.
The winner of the semi-finals, which start on September 14, will face the New Zealanders to try to claim the silver ewer awarded to the winner of the America's Cup.
