The opening day of practice for Mazda MX-5 Cup and Michelin Pilot Challenge will be the warmest day of the event, with high temperatures reaching into the lower 80s, thanks to a south wind at 10 to 20 mph. A cold front will be approaching the area from the northwest, and there is a slight chance of a late day shower. Most of the showers with the front will come after sunset, and will exit before sunrise on Thursday, so I don't expect that rain will have an impact on the practice sessions.
Behind the cold front, temperatures will be quite a bit cooler as winds switch around to the northwest. For Thursday through Saturday, highs will be in the lower to mid 60s, with lows in the 40s. This is about 6-10 degrees colder than normal at Daytona, but not as cold as last year's race which had lows in the 30s.
Sunday will be very nice, with temperatures warming into the mid 70s, under partly sunny skies.