The Weather of May 2026 - A cloudy and relatively hotter May

May 2026 was characterised by cloudier than usual weather with localised heavy rain. The mean amount of cloud in the month was 82 percent, 6 percent above the normal of 76 percent. The rainfall over the territory was highly uneven. The total rainfall recorded at the Hong Kong Observatory Headquarters in the month was 227.2 millimetres, about 78 percent of the normal of 290.6 millimetres, whereas rainfall exceeded 500 millimetres over the North District. The accumulated rainfall recorded in the first five months of the year was 586.8 millimetres, slightly below the normal of 590.9 millimetres for the same period. While the monthly mean temperature of 26.8 degrees was 0.5 degrees above the normal of 26.3 degrees, under the influence of a hot southerly airstream and an anticyclone aloft, there were 6 consecutive hot nights starting from 23 May, one of the highest on record for May. Attributed to the well above normal temperatures in March and April, the spring of this year from March to May was much warmer than usual. The mean temperature of 24.6 degrees and mean minimum temperature of 22.9 degrees were both the second highest on record for the same period, while the mean maximum temperature of 27.2 degrees was the fourth highest.

Under the influence of an easterly airstream and a band of clouds covering the coast of Guangdong, local weather was mainly cloudy with one or two rain patches on the first two days of the month. A trough of low pressure developed into a cold front and moved across the coastal areas on the afternoon of 3 May. While there were sunny intervals in the morning, the arrival of the cold front brought occasional heavy showers and squally thunderstorms later that day. Around 40 millimetres of rainfall were recorded over many places, and rainfall even exceeded 60 millimetres over Lantau Island and the eastern part of Hong Kong Island. Under the influence of the associated northeast monsoon, local weather was mainly cloudy with a few showers the next day and slightly cooler in the morning. Upper-air disturbances affected Guangdong on 5 May. Locally, it was cloudy with occasional showers. Showers were more frequent in the morning with more than 20 millimetres of rainfall recorded over many places. In the midst of the downpour, the temperature at the Observatory dropped to a minimum of 19.7 degrees in the morning, the lowest of the month. The northeast monsoon continued to affect the coast of Guangdong on 6 - 7 May. Locally, it was mainly cloudy with one or two light rain patches on 6 May as a band of clouds covered the coast of Guangdong. With the band of clouds thinning out and the northeast monsoon moderating, local weather became hot in the afternoon with sunny periods on 7 May.

A trough of low pressure brought showers and thunderstorms to Guangdong on 8 May. Locally, it was mainly cloudy with a few showers and was hot with sunny periods during the day. A fresh to strong easterly airstream brought slightly cooler weather to the coast of Guangdong the next day. Besides, an area of thundery showers associated with the trough of low pressure affected the vicinity of the Pearl River Estuary in the morning. Locally, it was cloudy with showers. Showers were heavy at times at first with a few thunderstorms. More than 30 millimetres of rainfall were recorded over many places, and rainfall even exceeded 70 millimetres over Kwai Tsing and parts of Lantau Island. With the weakening of the trough of low pressure and the moderation of the easterly airstream, local weather remained cloudy and showers abated on 10 May. As an anticyclone aloft over the northern part of the South China Sea extended northwards, local weather turned generally fine and hot on 11 May and remained so in the following two days.

Affected by upper-air disturbances on 14 May and a trough of low pressure the next day, local weather was mainly cloudy with occasional showers and squally thunderstorms. More than 20 millimetres of rainfall were recorded over the eastern part of Hong Kong and rainfall even exceeded 50 millimetres over Lamma Island during 14 and 15 May. Under the influence of a strong easterly airstream, the weather in Hong Kong became windier and showery on 16 - 18 May. With the easterly airstream replaced by a southerly airstream and upper-air disturbances affecting the coast of Guangdong, local weather was mainly cloudy with occasional showers and a few squally thunderstorms on 19 May. Showers were heavy at times during the day with more than 30 millimetres of rainfall recorded over many places and rainfall even exceeded 50 millimetres over Lantau Island and Sha Tin. While local weather was hot with sunny intervals on the afternoon of 20 May, thundery showers associated with upper-air disturbances brought more than 200 millimetres of rainfall to the North District that night. There were more than 50 millimetres of rainfall generally over the territory and even exceeded 100 millimetres over many parts of the New Territories on the morning of 21 May. The outbreaks of heavy showers prompted the issuance of the first Red Rainstorm Warning Signal of the year that morning. With the departure of the upper-air disturbances, there were bright periods in the afternoon on 21 May.

Under the influence of a hot southerly airstream and an anticyclone aloft, apart from isolated showers, local weather was hot with sunny periods on 22 - 26 May. The anticyclone continued to bring mainly fine and very hot weather on 27 - 29 May. With plenty of sunshine and under light wind conditions, the temperature at the Observatory rose to a maximum of 34.1 degrees in the afternoon of 29 May, the highest of the month. Temperatures over many places even rose to 35 - 37 degrees. However, heat-triggered thundery showers brought more than 30 millimetres of rainfall to many parts of the territory that night, and rainfall even exceeded 50 millimetres over the North District and the Central and Western District. With an easterly airstream setting in, the maximum temperatures were slightly lower over the territory on the following two days. Apart from sunny intervals, there were also a few showers associated with upper-air disturbances on 31 May. Showers were heavier in some areas with thunderstorms. Rainfall exceeded 10 millimetres over the western part of the New Territories and Lantau Island.

Two tropical cyclones occurred over the South China Sea and the western North Pacific in May 2026.