The United States Grand Prix is shrouded in uncertainty as a result of heavy thunderstorms in Texas on the periphery of Hurricane Patricia.
Second practice at the Circuit of the Americas near Austin was cancelled as a result of the storms.
With up to 30cm of rain forecasted to fall on Saturday, qualifying could be postponed until Sunday.
Officials have not yet made specific contingency plans because the weather forecast is changing so frequently.
However, governing body the FIA is open to the possibility of changing the weekend timetable to try to ensure qualifying can take place if there is a window of dry weather.
The
worst of the weather is expected to subside by Sunday, when the race is scheduled for 1400 local time (1900 GMT).
If it is not possible to run qualifying on Saturday, officials have the choice of running it on Sunday morning before the race, or deciding the grid by another method.
Hurricane Patricia, which is on its way to Mexico, is one of the strongest tropical storms on record.
The storm is even raising concerns about the forthcoming race in Mexico next weekend.
If it causes extensive damage in the capital Mexico City, there could be a knock-on effect for the race at the
Autodromo Hermanos Rodriguez track, which is hosting a grand prix for the first time since 1992