Last month was wetter than usual, seeing nearly 400mm of rain.
The Hong Kong Observatory said the figure was 31% above normal.
However, the accumulated rainfall recorded in the first five months this year was 533.8mm, 17% below normal.
The weather in May was unstable with the maximum temperature of 31.6 degrees Celsius.
With the passage of a trough of low pressure across the coast of Guangdong, local weather deteriorated with heavy showers and squally thunderstorms on May 24.
On that day, the Observatory issued the first Black Rainstorm Warning Signal for this year.
