Planes continue to take off and land at the Daytona airport located beside the track.
Meteorologist Brian Neudorff told USA TODAY Sports he's "very concerned" about the threat of severe weather, which is currently present in the form of a tornado warning just north of the track.
"This (smaller cell) may move through, but we continue to see some very nasty weather to the north," he said. "Severe weather is not out of the question in the next hour to hour and a half."
The safety of Sprint Cup fans during inclement weather came under scrutiny when a fan was killed by a lighting strike after the Aug. 5, 2012 race at Pocono Raceway.
A severe weather warning was issued at 4:12 p.m., and the track said it made announcements about the storm. But the grandstands weren't evacuated before NASCAR stopped the race at 4:54 p.m. The fatal strike occurred at 5:01 p.m. in a parking lot behind the grandstands, and nine more were transported to hospitals after being injured by other lightning strikes.
Neudorff said he believes NASCAR could still race tonight, but the threat of thunderstorms in the area will linger until approximately 6 p.m. The Idaho-based "unofficial NASCAR weatherman" said the cell north of the track might clip Daytona.
"The one that has a tornado warning is on a trajectory to get somewhat close to the track," he said. "Meanwhile, the storm right over the track is moving extremely slow. ... We could be in for a long red flag right now."
The race is scheduled for 200 laps. NASCAR can declare a winner if a race reaches halfway, which would be 100 laps.
The race started under cloudy skies and forecasts called for a 60% chance of showers and thunderstorms.
But less than an hour into the race, heavy rains began moving in on the track, soaking pit road, the garage area and the more than 150,000 fans in attendance.
Since the superspeedway is equipped with lights, NASCAR probably will push to get the race completed Sunday no matter how long the wait.
The Air Titan, which made its debut last season, is available to help dry the track.
The system works with two sets of identical equipment on opposite sides of the track that move in the same direction for one complete pass. The diesel-powered system uses air compression to move water down and off the track.
The 2012 Daytona 500 was the first to be delayed by rain. When it finally started on a Monday night, it was delayed for two hours because of a massive fire sparked by Juan Pablo Montoya's collision with a jet dryer as it removed debris under caution. Last year, NASCAR senior vice president Steve O'Donnell said jet dryers still would be used to blow debris off the track, though there is hope the Air Titan eventually will be used for the same purpose.
Before the delay, two caution periods interrupted the race.
Rookie Kyle Larson, who had popped the outside wall earlier, spun off the track to the inside on lap 23, causing the first caution. During the caution period, Matt Kenseth spun while trying to enter his pit and wound up backward in the stall, where the team serviced the car as it normally does.
The pit sequence also saw Marcos Ambrose and Danica Patrick making slight contact as Ambrose left his pit and Patrick arrived in hers.
The second caution flag appeared when Martin Truex Jr.'s engine blew on lap 31. Truex was the race's second-place qualifier. Light rain began falling during the caution.
Hamlin, one of the pre-race favorites, found some early-race trouble as a piece of debris caught on his grille. He dropped out of the lead to pick up some air from other cars and sweep the paper off the grill.
EARLIER: Pole winner Austin Dillon, returning the car number 3 to Sprint Cup racing, led the first lap with Denny Hamlin and Matt Kenseth following.