An cold front will be approaching from the north on Friday. Daytona will be ahead of the front during the day, so a southwest wind and pleasant temperatures in the lower 70s can be expected. A few light showers or sprinkles may be possible on Friday, but I don't expect they would be enough to have any impact.
The front will stall across central Florida on Friday night, and a low pressure system will track long it, from the Gulf to the Atlantic. This will bring rain to Daytona starting Friday night, with periods of on/off rain through the day on Saturday. Most of this rain is expected to be light, maybe increasing to moderate at times. This could result in some periods where the testing will need to be stopped. At least it will be a good test for the Michelin rain tires. Breezy conditions are also expected on Saturday, with a north wind between 10 and 20 mph, gusting to 25 mph at times. Total rainfall amounts from Friday night through Saturday night are expected to be around a quarter of an inch.
The system will exit the area Saturday night, and drier air will move in, so the chance of rain will end before on-track action resumes on Sunday. Despite abundant sunshine, temperatures will be cool on Sunday, with highs struggling to reach 60 degrees.