By 4 p.m. the Rainville/Gammino Bizzarrini Iso Grifo A3C was in the top ten overall standings. As the traffic had thinned over the 5.2 mile circuit both Bizzarrini drivers were able to establish a set pace that they hoped would continue to move them up the ranks.
The Hall/Sharp Chaparral continued to lead at this time with the Graham Hill, Pedro Rodriguez Ferrari 330P second and the Ken Miles, Bruce McLaren Ford GT40 third. Positions had not changed for the top three by 5 p.m. but very dark clouds were approaching from the northwest and a storm was imminent. It became so dark that a few racers found it necessary to turn on their driving lights.
Charlie Rainville brought in the car for the scheduled 5 p.m. pit stop and driver change. Mike Gammino was delayed in taking over the car because mechanics found that, due to the extreme heat on the track, the brake calipers had become distorted. Changing the brake pads would need extra time.
Twenty-five minutes later the storm hit with surprising force. The initial winds exceeded 50 mph and causing the Good Year blimp, Mayflower, to stand straight up on its nose. The ground crew rushed to secure the air ship lest it break free from its mooring. A few of the tents and temporary structures in the spectator area were either blown away or blown over. One tent ended up in the branches of a nearby tree with its tie-down ropes and tent stakes still attached.
Then the rains descended like a gray wall of water on the track cutting visibility almost to zero. By most accounts at least 5 inches of rain fell during the early stages of the storm totally overwhelming the track’s drainage system.
Under these conditions race cars lap times began to double, then triple as the cars plowed through standing water on the track. Water levels reached eight inches or more in some areas. More than one car stopped on the track or sputtered into the pits with soaked ignitions and didn’t get going until their distributor and electrics were dried out.