The FIA said Friday and Saturday should stay hot and sunny, but Sunday in Miami could bring heavy rain and thunderstorms near the race start.
US rules can halt major outdoor events when lightning threatens, forcing spectators to leave and grounding the medical helicopter, which would stop on-track running.
The governing body said it is closely monitoring conditions, is confident the race can still run as scheduled, and could alter the start time to minimise disruption.
What is the plan to safely evacuate thousands of fans if a thunderstorm suddenly hits the Miami circuit mid-race?
Can F1's rigid helicopter rule and strict US lightning laws coexist, or is the Miami race schedule in jeopardy?
How will new wet-weather rules banning 'boost mode' alter the outcome of a rain-soaked Miami Grand Prix?