AUSTIN, Texas (AP) When the rain came, all Lewis Hamilton could do was wait.
And wait. And wait. And then hope all this rain won't impact his world title hopes.
Hamilton completed only four practice laps Friday morning for the United States Grand Prix, a frustrating first day before a weekend where he hopes to clinch his second consecutive world championship and third overall.
Torrential rain and lighting forced race officials to cancel the afternoon practice session when it was determined the medical helicopter at the Circuit of the Americas would not be able to fly in the poor conditions.
Hamilton's Mercedes teammate, Nico Rosberg, turned in the fastest lap during the wet but still drivable morning session with a time of 1 minute, 53.989 seconds. Hamilton was on the course only a few minutes, and went to the garage likely figuring he'd get a better chance in the afternoon. Turned out his best lap of 1:55.693, good for fifth, would have to stand for the day.
Storms could affect the entire weekend, from qualifying Saturday to the race Sunday.
''I don' think I've ever seen it rain like this,'' Hamilton said. ''We've got very little information to work with now, so the rest of the weekend will be very intense.''
In the morning session, the cars sent towering plumes of wet spray behind that limited visibility early on. Even when he was by himself, Hamilton nearly spun around his back end as he braked into a corner.
''It's pretty greasy,'' Red Bull's Daniel Ricciardo radioed to his team. Williams' Valtteri Bottas slid as he tried to stop at his garage, causing a crew member to leap out of the way.
The rain came roaring back just as the teams were getting ready for the second practice before officials announced an indefinite delay. Running water swamped the paddock drainage system and created large puddles near the grandstand where wading ducks soon outnumbered fleeing fans.
Track officials have developed an evacuation plan for fans and marshals if needed throughout the weekend.
''I've never faced the likelihood that marshals would have to leave their posts because of lighting,'' said Charlie Whiting, FIA F1 race director. ''This is a first for me.''
Hamilton needs to score nine more points that Ferrari's Sebastian Vettel and two more than Rosberg to win the championship. Vettel is already facing a 10-spot penalty grid because Ferrari is using a fifth engine this season. Rosberg won the pole position at this race last year, only to be overtaken by Hamilton for the win.
''For me it wasn't a bad day. Let's see what tomorrow brings,'' Rosberg said.
It could very well be more rain. Race officials expected to keep a close watch on the weather radar.
''The one thing we know about meteorologists is that they're always wrong,'' Jason Dial, president and chief executive of the Circuit of the Americas. ''But are they going to be wrong on the light side or the heavy side?''
Former three-time world champion Jackie Stewart recalled his own days racing in the rain, remembering one particular race in Germany.
''We were doing 180 mph just because you knew where to go in the racetrack,'' Stewart said.
If drivers can't see, safety has to come first, Stewart said. But if it's just wet, the conditions will make things ''just a little bit more challenging for them.''