May was drier than usual with total monthly rainfall of 194.4 millimetres, 122.3mm below the normal figure. This was despite the deluge on May 8 which saw the issuance of the first Black Rainstorm Warning in three years.

Accumulated rainfall since January 1 was 548.7mm, about 11% below the normal figure of 616.5mm.

Under the influence of a warm maritime airstream, the weather was hot and fine in the first three days of May. However, a rain band associated with an upper-air disturbance swept through Hong Kong on May 8 and brought widespread heavy rain and squally thunderstorms.

Rain was heaviest when an upper air vortex developed and passed over Hong Kong, bringing more than 100mm to the urban areas and over 150mm to Lantau Island, Kwai Tsing and Sai Kung in about two hours.

Tornado reported

There were reports of a tornado in Sheung Sze Wan and the sea area off Wang Chau in eastern Hong Kong. A 24-metre fishing vessel sank in the inclement weather and one person went missing. There were also 22 flood reports, mostly in Kowloon.

The weather rapidly grew fine on May 9 as a ridge of high pressure established itself over southern China. The weather turned cloudy again on May 17 and 18, and a trough of low pressure developed over the coast of Guangdong on May 19 and brought showers to Hong Kong.

A ridge of high pressure built up over southeastern China on May 23, bringing fine and hot weather to Hong Kong. The weather was mainly fine for the rest of the month, but interrupted by showers and thunderstorms on May 28 and 29.

With prolonged sunshine, the maximum temperature on May 31 soared to 32.4 degrees, the highest so far this year.