US Open organizers say that they are more committed than ever to putting a cover over Arthur Ashe Stadium to prevent future washouts at the Grand Slam tennis tournament.

Tournament chief executive Arlen Kantarian said they just completed a third study on a new roof but declined to give details on what the cost would be or when the roof would be built.

"At this point it is a question of when and not if," said Kantarian.

"We believe this tournament has reached the point where we are looking seriously at putting a roof on the Arthur Ashe Stadium,” Kantarian added.

Kantarian was speaking after the remnants of tropical storm Hanna hit the New York area on Saturday afternoon in the middle of the men's semi-final between Andy Murray and Rafael Nadal.

He said they would take advantage of new technology in building materials to construct a lightweight see-through roof that would keep the players, officials and fans dry.

Asked if the roof would be ready by next year, Kantarian answered, "No."

"Now we are more optimistic," he said.

"It would cost some 100 million dollars for just nine cancelled sessions in the last 20 years of this tournament, but this is something we need to do,” he added.

Organizers decided to stagger the start of the two men's semi-finals on Saturday instead of beginning them both at 11 am before the rains came.