The decision to move the start time of the race was made by commercial rights holder F1 and governing body the FIA on Saturday evening in Miami.
A statement from F1 and the FIA said the decision was made because “the weather forecast (predicts) heavier rainstorms later in the afternoon close to the original planned race start time”.
The statement added: “This decision has been taken to ensure the least amount of disruption to the race, and to ensure the maximum possible window to complete the grand prix in the best conditions and to prioritise the safety of drivers, fans, teams and staff.”
The aim is to try to finish the race before the worst of the weather arrives, which is forecast to be at about 15:00 local time (20:00 BST), one hour before the original start time.
That heavy rain, once it starts, is expected to stay for hours, so the fear was that sticking with the original start time would have meant the race could not be run.
Moving it forward, the race is still likely to be wet, but the hope is the conditions will be acceptable for running the cars.
F1 cars do run in the rain, but the limiting factor is always visibility from the vast amounts of spray thrown up by the cars, as well as aquaplaning if the amounts of standing water are significant enough to force the low-running cars to effectively float on top of water on the track.
Norris’ team-mate Oscar Piastri added: “It’s obviously going to be a voyage into the unknown for everybody. When it rains here, it normally is pretty torrential, so it could be an interesting day.
“It’s just going to be what happens with the power-unit, how you get power, where you get power is in a computer’s hands.
“Just making sure that that does roughly what we expect. Obviously, the margin for error when it’s wet is significantly smaller.”