Hong Kong experienced particularly tumultuous weather yesterday as a hot, hazy, smog-ridden early afternoon gave way to thunderstorms with major lightning - even hailstorms - in some districts.
The day began fine. Early readings of the air pollution index in Tung Chung were at around 25, considered low, but the hot weather caused by the presence of Typhoon Kaemi near Taiwan caused it to soar to 136 by 4pm, according to Environmental Protection Department officials.
In Central and Western District, the index reached a high of 113 around 3pm before a heavy downpour caused it to plummet to one-third of the level by 5pm.
Sai Kung residents saw 1,550 lightning strikes in two hours from 3pm and also experienced a 15-minute hailstorm.
Lee Kwok-lun, scientific officer with the Hong Kong Observatory, said public reports told of hail the size of 'a fingernail'.
'Because the thunderstorm is a system of convection, it is very strong and will also lead to the formation of hailstones in the atmosphere,' Mr Lee explained. 'It is not that rare. Between 1967 and now, we have had more than 30 hailstorms in Hong Kong.'
Convection is the term meteorologists use to describe the rise of heat and moisture, especially by updrafts and downdrafts in an unstable atmosphere.