The Weather of July 2019

July 2019 was much hotter than usual in Hong Kong, mainly attributing to the warmer than normal sea surface temperature over the northern part of the South China Sea. The monthly mean minimum temperature of 27.7 degrees was 0.9 degree above the normal figure of 26.8 degrees, the highest on record for July. The monthly mean temperature of 29.5 degrees was 0.7 degree above the normal figure of 28.8 degrees, one of the sixth highest on record for July. The month was also cloudier than usual with the mean amount of cloud of 79%, about 10% above the normal figure of 69% and one of the fifth highest on record for July. The duration of bright sunshine in the month was only 150.5 hours, about 29% below the normal figure of 212.0 hours and the seventh lowest on record for July. The monthly rainfall was 328.5 millimetres, about 13 percent below the normal of 376.5 millimetres. The accumulated rainfall recorded in the first seven months of the year was 1437.9 millimetres, slightly lower than the normal figure of 1473.3 millimetres for the same period.

Affected by an area of low pressure over the northern part of the South China Sea, there were sunny periods and showers as well as isolated thunderstorms on the first day of the month. Meanwhile, the area of low pressure developed into a tropical depression and was named Mun on 2 July. It moved generally westward across Hainan Island and entered Beibu Wan on 3 July. Mun made landfall over the northern part of Vietnam and weakened into an area of low pressure over inland on 4 July. Under the influence of the rainbands associated with Mun, it was cloudy with occasional heavy showers and thunderstorms on 2 – 4 July. More than 100 millimetres of rainfall were recorded over most parts of the territory in these three days.

With the prevalence of a southwesterly airstream, the weather of Hong Kong was a mixture of sunshine and showers on 5 – 9 July. Under the influence of a trough of low pressure, local weather became showery with a few thunderstorms on 10 – 11 July. More than 60 millimetres of rainfall were recorded over Lantau Island and parts of the New Territories in these two days.

Dominated by an anticyclone aloft southeastern China, apart from a few showers, local weather turned fine and progressively became very hot from 12 – 18 July. With plenty of sunshine and light winds, the maximum temperature at the Observatory soared to 35.0 degrees on 18 July, the highest of the month. The oppressive heat also triggered thundery showers in that evening. While the weather remained very hot with sunny intervals on the morning of 19 July, high temperature again triggered heavy showers and squally thunderstorms in that afternoon. More than 30 millimetres of rainfall were recorded over many places, and rainfall even exceeded 50 millimetres over the western part of the New Territories. A trough of low pressure continued to bring showery weather with localized heavy rain to Hong Kong on 20 – 21 July. During these two days, more than 40 millimetres of rainfall were recorded over North District, Sai Kung and Southern District, rainfall even exceeded 100 millimetres over Sha Tau Kok.

Affected by an upper-air disturbance, the weather of Hong Kong was a mixture of sunshine and showers on 22 – 24 July. With the strengthening of the anticyclone aloft southeastern China, local weather became generally fine and very hot apart from isolated showers in the next three days. As the anticyclone aloft weakened, it was mainly cloudy with a few showers and thunderstorms on 28 – 29 July. Meanwhile, an area of low pressure developed into a tropical cyclone over the northern part of the South China Sea on 30 July and was named Wipha. With Wipha moving towards Hainan Island, local weather deteriorated gradually and became windy with outbreaks of squally heavy showers and thunderstorms on the last two days of the month. The outer rainbands associated with Wipha brought more than 100 millimetres of rainfall to most parts of the territory on 31 July and the rainfall over Tseung Kwan O, Wong Tai Sin and Tai Wai even exceeded 200 millimetres. In the midst of the downpour, the temperature at the Observatory dropped to a minimum of 24.5 degrees on 31 July, the lowest of the month.

Four 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 1.6. Monthly meteorological figures and departures from normal for July are tabulated in Table 2.

Warnings and Signals issued in July 2019

Extract of Meteorological Observations in Hong Kong for July 2019