US Open chief Jim Hyler will be hoping for the smallest number of golfers to make the cut as he tries to finish the Open on time.

After losing most of Thursday's play to heavy rain as an inch of water fell on the Long Island course, tournament officials are bracing for the possibility of even more hitting the Black course at Bethpage State Park.

United States Golf Association meteorologists were last night tracking a low pressure weather system heading towards Long Island from the Great Lakes region to the north west of New York.

Carrying thunderstorms and showers, they say there is an 80% chance of rain falling on the course, dropping a further three-quarters to an inch and a quarter in the process.

A further loss of playing time is likely to extend the playing of the regulation 72 holes into Monday, regardless of the need for an 18-hole play-off and with US Open championship rules providing for a 36-hole cut of the 156-man field to the low 60 scorers and ties and any player within 10 strokes of the leader, that could mean a long backlog of rounds to be played.

"We'll play all the golf we possibly can," said Hyler, USGA vice president and chairman of its championship committee.

"Obviously if we get hit with that kind of rain, that will severely impact our plans. But if we get lucky on the weather, maybe somehow we dodge a lot of that.

"There is a chance that we could finish Round 2 (on Saturday). I think beyond that, anything would be pure speculation, just based on the forecast and also the size of the cut."

As of last night, as the early second round starters reached the halfway mark in their rounds, more than 100 players would survive under the 10-shot rule, within distance of Mike Weir and Lucas Glover's lead at five under par.

"If we had a small cut, say 60 or low 60s, we'd have more flexibility than if we had 100 people making the cut," Hyler said.

"So I think any speculation beyond tomorrow, that is what it is, speculation."