The No 3 strong-wind warning was hoisted last night as tropical storm Bebinca moved closer to the city, raising the prospect of heavy rain and squalls.
A glass pane on Wan Chai's Convention and Exhibition Centre measuring 1 metre by 5 metres cracked into pieces at about 9pm. No one was injured.
The Observatory raised the signal at 8.20pm, more than 12 hours after raising the No 1 standby signal at 7.40am. That left organisers of the Dragon Boat Carnival wondering whether to cancel it.
"Bebinca dumped rain on Hong Kong this afternoon," Observatory senior scientific officer Song Man-kuen said yesterday. "We expect the storm will get stronger as it moves along 300 kilometres southwest of the city tomorrow."
The storm is forecast to make its way along the coast of western Guangdong towards Hainan , with winds easing tomorrow but squally showers persisting. It drew near the city after a sweltering day that saw temperatures rise to 33.5 degrees Celsius in Tsim Sha Tsui at 3pm. The mercury will hover between 25 and 29 degrees today, rebounding over 30 on Wednesday when forecast heavy rain is expected to abate.
In March, the Observatory predicted that four to seven tropical cyclones would affect Hong Kong this year.
The Tourism Board said earlier that it would cancel dragon boat races on Victoria Harbour if signal No3 or a red or black rainstorm warning was hoisted.
The three-day event, which began yesterday, has drawn more than 5,000 entrants from local groups and 11 territories around the world. Beer-drinking competitions and a rock concert were also scheduled.
Planned features on Sunday included a celebrity "bathtub race" featuring lawmakers, artistes and business leaders, including Ocean Park chairman Allan Zeman. Teams of two were to row their tubs along a 100-metre route, also competing for fancy dress awards.
Meanwhile, board chairman Peter Lam Kin-ngok, whose firm Eastasia Entertainment is one of the organisers of a July 1 rock concert, asked people not to "politicise" the event. The Hong Kong Dome Festival is seen as a political tool to keep youngsters away from the pro-democracy march.