The Weather of May 2019

With more than usual moisture content in the lower atmosphere over southern China, May 2019 was gloomier than usual in Hong Kong. The mean amount of cloud in the month was 83 percent, 7 percent above the normal of 76 percent and the duration of bright sunshine in the month was only 83.1 hours, about 41 percent lower than the normal figure of 140.4 hours and the second lowest on record for May. With less sunshine and the prevalence of the cooler easterlies in the early part of the month, the month was cooler than normal with the monthly mean temperature of 25.3 degrees, 0.6 degree below the normal figure of 25.9 degrees. Overall, attributing to the well above normal temperatures in March and April, the spring of Hong Kong in 2019 was still much warmer than usual with the mean temperature from March to May 2019 reaching 23.7 degrees, 1.2 degrees above the normal and one of the fifth highest on record for the same period. The monthly rainfall was 234.6 millimetres, about 23 percent below the normal of 304.7 millimetres. The accumulated rainfall recorded in the first five months of the year was 680.3 millimetres, about 6 percent above the normal figure of 640.8 millimetres for the same period.

With the thinning out of the cloud band covering the coast of Guangdong, the weather of Hong Kong was mainly cloudy with sunny intervals during the day on the first day of May. The weather became relatively cooler during 2 – 8 May under the showery weather and the influence of a fresh to strong easterly airstream. The weather turned more unsettled with heavy showers and squally thunderstorms on 7 – 8 May due to the passage of an upper-air disturbance over southern China. More than 40 millimetres of rainfall were recorded over parts of the territory on these two days. Under the rain, the temperature at the Observatory dropped to a minimum of 18.9 degrees on 7 May, the lowest of the month.

With the departure of the upper-air disturbance, showers lessened with sunny intervals and rising temperatures on 9 - 10 May. Under the influence of a drier easterly airstream, local weather became generally fine and hot on 11 - 12 May. After a cloudy interlude on 13 May, apart from isolated showers, it was hot with sunny periods on 14 - 19 May under the prevalence of the southwesterlies. There were also fog patches on 14 - 16 May. With plenty of sunshine in the afternoon, the maximum temperature at the Observatory soared to 32.3 degrees on 18 and 19 May, the highest of the month. The daily minimum temperature of 29.2 degrees on 19 May was the highest on record for May.

Under the influence of a trough of low pressure lingering over the south China coast, the weather of Hong Kong deteriorated again with occasional heavy showers and squally thunderstorms on 20 - 23 May. Affected by an easterly airstream over the coast of Guangdong, it was mainly cloudy with some showers on 24 - 25 May.

With an unstable southerly airstream replacing the easterly airstream over the coast of Guangdong, there were heavy showers and squally thunderstorms in Hong Kong on 26 May. Around 20 millimetres of rainfall were recorded over most parts of the territory on that day and the rainfall over the western part of the New Territories even exceeded 40 millimetres. Unsettled weather associated with a trough of low pressure over the coastal areas of Guangdong affected the region on 27 - 28 May. Locally, outbreaks of heavy showers and squally thunderstorms brought more than 60 millimetres of rainfall to most parts of the territory on these two days. Rainfall even exceeded 120 millimetres over Tuen Mun, Yuen Long and Lantau Island. With the trough of low pressure lingering over the coastal areas of Guangdong, the weather in Hong Kong remained showery with isolated thunderstorms on the last three days of the month.

Sea fog near Lei Yue Mun on 15 May 2019

Sea fog near Tai Koo Shing on 15 May 2019

There was no tropical cyclone over the South China Sea and the western North Pacific in the month.

Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.4. Monthly meteorological figures and departures from normal for May are tabulated in Table 2.

Warnings and Signals issued in May 2019

Extract of Meteorological Observations in Hong Kong for May 2019