Forecasts at 0600 ET on Wednesday showed heavy storms over Miami on Sunday morning and afternoon before the 16:00 local start of round four.
The weather system is expected to sweep across the eastern United States, reaching Florida after crossing Alabama, Louisiana, Mississippi and the panhandle.
Other Miami sessions are forecast dry in temperatures in the low-to-mid 30s Celsius. Last year's sprint was delayed by storms, with Charles Leclerc crashing before the start.
Beyond rain, could a single lightning strike force the cancellation of the entire Miami Grand Prix?
Is the predicted Miami deluge a catastrophic threat or the key to an all-time classic race?
With new wet-weather rules debuting, could the Miami storm crown an unexpected F1 champion?
What is the true financial cost if Miami's celebrity-filled race week ends in a complete rainout?
Why do official F1 rain forecasts so dramatically contradict other major weather predictions for Miami?
As F1 fears a washout, could this same storm be the answer to Florida's historic 25-year drought?