Heavy rain started to fall on Daytona International Speedway as the Rolex 24 entered its 15th hour.
All teams have now the switch to wet Michelin tires after an anticipated weather front reached Daytona from the southwest.
The rain began to coat the 3.5-mile circuit at around 4:40 a.m local time before intensifying over the next 20 minutes and is expected to persist through the morning.
Some cars, including the No. 66 Ford GT that was running second in GT Le Mans and the LMP2 podium-contending No. 81 DragonSpeed Oreca 07 Gibson, have had off-track moments in the challenging conditions.
Felipe Nasr currently leads the race in the No. 31 Whelen Engineering Cadillac DPi-V.R, almost two minutes ahead of Ricky Taylor in the No. 7 Team Penske Acura ARX-05 DPi.
Shortly before the rain, the No. 55 Mazda RT24-P DPi spun out of contention at the international horseshoe.
Olivier Pla was pushing to return the Joest-run car onto the lead lap after an earlier fuel leak issue, but the Frenchman spun after contact with another car.