Chief Secretary Eric Chan on Wednesday said heavy rain and thunderstorms on Tuesday developed rapidly and it was difficult for authorities to make clear predictions.

Speaking to reporters at the Legislative Council after an antechamber exchange session, Chan said the SAR has a comprehensive, well-established and effective mechanism for handling extreme weather conditions.

He said the steering committee on handling extreme weather meets when possible extreme weather conditions are predicted, so that various departments can get prepared as soon as possible.

“The heavy rain yesterday developed rapidly and in a sudden between 8am and 9am, and the heavy rainfall was concentrated in several districts. It's hard to predict the situation clearly beforehand,” Chan said.

“Actually, after the Black Rainstorm Warning was issued, our emergency co-ordination and command centre was activated immediately, and various departments took immediate actions. Despite the flooding, fallen trees and obstruction on some roads, the problems were solved quickly.”

Meanwhile, the observatory said it is hard to predict the time and location of rain and thunderstorms due to their random nature, as well as technological limitations.

On an RTHK programme, assistant director of the observatory Cheng Yuen-chung said Tuesday’s Black Rainstorm Warning was triggered by a broad trough over the South China coast which allowed rain and thunderstorms to develop rapidly.

“High randomness is a characteristic of heavy rain... the rain mainly affected southeastern parts of Hong Kong, but if it moved a bit to the north, more places would have been affected,” Cheng said.

“Eastern District, Southern District and Lamma Island saw extremely heavy rain reaching 100 millimetres in an hour yesterday, higher than the rainfall indication of 70 millimetres per hour of the Black Rainstorm Warning. If the rainstorm area moved a little, more places would have been affected by heavier rain.”

Cheng also said that because the rainstorm lingered and continued to intensify, it was difficult to forecast its movements.