May was characterised by cloudier-than-usual weather with localised heavy rain over parts of the New Territories, the Hong Kong Observatory said today.

The mean amount of cloud in the month was 83%.

While over 700mm of rain fell over parts of Sai Kung, the monthly rainfall recorded at the observatory was only 292.6mm, near the normal figure of 290.6mm.

The accumulated rainfall recorded in the first five months of the year was 582.1mm, slightly below the norm of 590.9mm for the same period.

The monthly mean temperature was 26 degrees Celsius, slightly below the normal figure of 26.3.

Attributable to the well-above-normal temperatures in March and April, spring time from March to May was much warmer than usual.

The mean temperature of 24.5 degrees Celsius, mean minimum temperature of 22.7 degrees Celsius and mean maximum temperature of 27 degrees Celsius were respectively the second, one of the second and the fourth highest on record for the same period.

On the morning of May 1, under the influence of a trough of low pressure, the city's weather was unsettled with heavy showers and severe squally thunderstorms. More than 30mm of rain fell over Hong Kong, exceeding 50mm over the eastern part of the city. Gusts exceeding 100km per hour were also recorded on Cheung Chau. Under the rain, temperatures at the observatory dropped to a minimum of 22.4 degrees Celsius - the lowest for the month.

On May 4, persistent thundery showers affected the vicinity of the Pearl River Estuary areas with more than 100mm of rainfall recorded over many places and even exceeding 400mm over parts of Tseung Kwan O. The heavy rain necessitated the issuance of the first Red Rainstorm Warning Signal of the year. In the midst of the downpour, the temperature at the observatory dropped to the month’s lowest of 22.4 degrees Celsius again.

The showers were particularly heavy on May 21, resulting in over 50mm of rainfall recorded over most parts of the city. Rainfall even exceeded 200mm over parts of Lantau Island. With the departure of the upper-air disturbance, the showers abated with bright periods on the afternoon of May 26.

A trough of low pressure moved across the coast of Guangdong on May 28, bringing heavy showers and thunderstorms to Hong Kong. With the trough of low pressure moving to the northern part of the South China Sea, the local weather was hot with sunny intervals during the day, with temperatures at the observatory rising to 32 degrees Celsius - the highest of the month.

In the afternoon on May 30, a broad area of low pressure over the central to northern part of the South China Sea strengthened into a tropical depression, and the Observatory issued the first tropical cyclone warning signal of this year. The tropical depression intensified into a tropical storm and was named Maliksi on May 31. With Maliksi edging towards the coast of western Guangdong, the local weather deteriorated gradually, with rainfall exceeding 50mm over parts of the New Territories on the same day.

Two tropical cyclones occurred over the South China Sea and the western North Pacific in May, the observatory added.