Hong Kong braces for major cold front, 'Shi Hu Feng' squall lines

The Hong Kong Observatory forecasts a cold front crossing the Guangdong coast next Tuesday, bringing stronger winds, squally showers, and gradually falling temperatures through mid-to-late next week. Lows are expected to drop to 17 degrees on Friday and Saturday.

The Observatory’s weather blog yesterday explained that under favorable conditions—low-level wind shear and high atmospheric instability—Hong Kong could experience "Shi Hu Feng," a local term for sudden, violent gusts and heavy rain from squall lines.

Squall lines are fast-moving bands of intense thunderstorms formed by multiple storm cells. 

They cause abrupt shifts in wind-direction, sharp wind-speed increases up to over 100 km/h, heavy rain, lightning, and sometimes hail or tornadoes.

Past events have caused casualties and damage; for example, a 2005 squall line in Kwai Chung produced gusts of 135 km/h, toppling containers and resulting in one death and two injuries.

Under a damp southerly airstream, early next week will remain warm and humid with scattered showers. 

A low-pressure trough over central China is already triggering rain and thunderstorms in the northern part of South China, with showers and storms possible in Hong Kong over the next one to two days.

A strengthening easterly flow, tomorrow will meet warmer, humid southerly air near the Pearl River estuary, creating convergence that may lift air and produce the year’s first notable widespread rain, though timing and location remain uncertain.

Showers are expected to ease later Saturday as the convergence zone shifts west. 

Southerly flow will then dominate early next week, keeping conditions warm, humid, and showery before the northeast monsoon arrives mid-to-late week with the cold front.

Tuesday’s temperatures are forecast at 19–24 degrees, a drop of about 4 degrees from Monday’s 23–26 degree range, with further cooling to 17-degree lows later in the week.