3 November 2020

The mean temperature for October 2020 was 25.6 degrees, close to the normal figure of 25.5 degrees. Mainly attributing to the heavy downpour on 5 October, the month was wetter than usual with the monthly rainfall of 142.4 millimeters, about 41 percent above the normal of 100.9 millimetres. The accumulated rainfall this year up to October was 2388.4 millimetres, about 2 percent above the normal figure of 2334.0 millimetres for the same period.

Under the influence of a strong easterly airstream, the weather of Hong Kong was mainly cloudy with sunny periods on the first day of the month. Affected by an anticyclone aloft, it was generally fine on 2 – 4 October. With plenty of sunshine, the maximum temperature at the Observatory rose to 31.9 degrees on 3 October, the highest of the month. A cold front moved across the coastal areas of Guangdong and brought heavy rain and squally thunderstorms to Hong Kong on the morning of 5 October. The heavy downpour also necessitated the issuance of the Red Rainstorm Warning in that morning. More than 50 millimetres of rainfall were recorded over many places in Kowloon and the rainfall recorded at the Hong Kong Observatory even exceeded 100 millimetres.

Under the influence of a fresh to strong northeast monsoon, the weather of Hong Kong was mainly cloudy and slightly cooler on 6 – 7 October. Dominated by a dry northeast monsoon, the weather became generally fine and dry during the day on 8 – 12 October. Meanwhile, an area of low pressure gradually developed into a tropical depression over the central part of the South China Sea on the afternoon of 11 October and later named as Nangka. It moved generally west-northwestward across the northern part of the South China Sea and intensified into a tropical storm on 12 October. Nangka moved across Hainan Island on the night of 13 October and entered Beibu Wan in the small hours the next day. Nangka made landfall over Vietnam on the evening of 14 October and weakened gradually into an area of low pressure over Indochina Peninsula the next morning.

Affected by the outer rainbands of Nangka, the weather of Hong Kong turned cloudy with a few rain patches on the night of 12 October. Rainy weather persisted on 13 October. Under the combined effect of Nangka and the northeast monsoon, local winds strengthened during the day with gale force winds over offshore waters and on high ground. The Gale or Storm Signal No. 8 was issued on the early morning of that day. With the departure of Nangka, the strong northeast monsoon continued to bring windy weather with a few rain patches to Hong Kong the next day.

Dominated by a dry northeast monsoon, apart from a few rain patches at night on 16 – 18 October, the weather was generally fine and dry during the day on 15 – 22 October with slightly cooler weather on 17 – 21 October. The temperature at the Observatory dropped to a minimum of 21.7 degrees on 21 October, the lowest of the month. Meanwhile, an area of low pressure gradually developed into a tropical depression over the seas east of the Philippines on 19 October and later named as Saudel. It moved across Luzon on the night of 20 October and entered the central part of the South China Sea the next morning. Saudel moved across the central part of the South China Sea and intensified gradually into a typhoon on the afternoon of 22 October. It continued to move generally westwards across the central part of the South China Sea and weakened into an area of low pressure over the seas east of the central part of Vietnam on morning of 26 October.

Affected by the cloud bands associated with Saudel and a dry northeast monsoon, local weather turned cloudier and slightly cooler but remained dry on 23 – 24 October. After the weakening of Saudel, the dry northeast monsoon brought generally fine, windy and dry weather to the territory in the next few days. Meanwhile, tropical cyclone Molave moved across the southern and central parts of the South China Sea on 26 - 28 October. Under the influence of the moisture spreading from Molave and a strong northeast monsoon, the weather of Hong Kong turned cloudier again with a few rain patches but remained windy on 28 – 29 October. With the dissipation of the rain band over south China coastal areas, local weather became mainly fine towards the end of the month.

Seven tropical cyclones occurred over the South China Sea and the western North Pacific in October 2020.

Details of issuance and cancellation of various warnings/signals in the month are summarized in Tables 1.1 to 1.5.  Monthly meteorological figures and departures from normal for October are tabulated in Table 2.