Owing to the stronger than normal upper-air anticyclone over southern China, October 2019 was exceptionally hot and sunny in Hong Kong. The monthly mean maximum temperature of 29.5 degrees, 1.7 degrees above the normal figure of 27.8 degrees, was the highest on record for October. The monthly mean temperature was 26.6 degrees, 1.1 degrees above the normal figure of 25.5 degrees and the second highest on record for October. The month was marked by sunny weather with the monthly total sunshine duration amounting to 230.7 hours, about 19 percent above the normal of 193.9 hours. With two heavy rain episodes respectively on 6 – 7 October and 13 – 14 October, the month was also wetter than normal with a monthly rainfall of 149.5 millimetres, about 48 percent above the normal of 100.9 millimetres. The accumulated rainfall this year up to October was 2382.7 millimetres, about 2 percent higher than the normal figure of 2334.0 millimetres for the same period.

Affected by an anticyclone aloft southern China, it was generally fine and hot on 1 – 5 October in Hong Kong. With plenty of sunshine, the maximum temperature at the Observatory soared to 33.2 degrees on 1 October, the highest of the month. Moreover, the daily mean temperature of 30.3 degrees on that day was the highest on record for October.

Under the influence of a strong easterly airstream and an upper-air disturbance, local weather became mainly cloudy with occasional heavy showers and squally thunderstorms on 6 – 7 October. More than 30 millimetres of rainfall were recorded over many places on 6 October, rainfall even exceeded 50 millimetres over Sai Kung and southern part of Hong Kong Island. With the anticyclone aloft strengthening again over southern China, apart from isolated showers, local weather was generally fine on 8 – 11 October. There were isolated thunderstorms on the afternoon of 12 October due to the weakening of the anticyclone aloft. About 20 millimetres of rainfall were recorded over Kowloon and the western part of Hong Kong Island on that day.

A cold front moved across the coast of Guangdong on the morning of 13 October and the associated northeast monsoon brought slightly cooler weather to the region. Locally, the weather became unsettled with occasional heavy showers and squally thunderstorms on 13 – 14 October. More than 30 millimetres of rainfall were recorded over many places on these two days, rainfall even exceeded 70 millimetres over parts of New Territories East and Hong Kong Island.

With the northeast monsoon strengthening gradually, apart from a few showers in the morning, the weather became generally fine and windy on 15 October. Dominated by the dry northeast monsoon, the weather of Hong Kong was generally fine and dry during the day on 16 – 27 October. A replenishment of the northeast monsoon reached the coastal areas of Guangdong later on 28 October. Locally, it was mainly cloudy with a few rain patches and relatively low visibility in some places. The strengthening of the northerlies also brought cooler weather to the territory that night. With the dry northeast monsoon prevailing over southern China, it was cooler and dry with sunny periods in Hong Kong for the rest of the month. The lowest temperature of the month, 20.3 degrees, was recorded on the morning of 29 October.

Five tropical cyclones occurred 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 1.5. Monthly meteorological figures and departures from normal for October are tabulated in Table 2.

Remarks :

Extremely high: above 95th percentile Above normal: between 75th and 95th percentile Normal: between 25th and 75th percentile Below normal: between 5th and 25th percentile Extremely low: below 5th percentile Percentile and 5-day running average values are computed based on the data from 1981 to 2010

Extract of Meteorological Observations in Hong Kong for October 2019