The Weather of July 2009

    July 2009 was warmer than usual. The mean temperature was 29.1 degrees, 0.4 degrees above the normal figure of 28.7 degrees. The total rainfall of 389.4 millimetres in the month was about 4 percent above the normal figure of 374.4 millimetres. The accumulated rainfall since 1 January was 1206.9 millimetres, about 16 percent below the normal figure of 1429.1 millimetres for the same period.

    Under the influence of a weak ridge of high pressure over the south China coastal areas, the weather in Hong Kong was generally fine for the first two days of the month. Affected by an active southwest monsoon, it turned mainly cloudy with a few showers on 3 July. A trough of low pressure over southern China brought cloudy weather with scattered showers and squally thunderstorms to the territory from 4 to 6 July.

    With the strengthening of a ridge of high pressure over southeastern China, local weather became fine and hot on 7 July apart from some showers in the morning. It remained sunny and hot for the ensuing three days.

    Tropical Storm Soudelor moved across the northern part of the South China Sea and passed at a distance of about 240 kilometres to the south of Hong Kong on 11 July. Local winds picked up from the east and there were occasional squally showers on that day. After Soudelor made landfall over Vietnam and weakened into a tropical depression on 12 July, local winds subsided gradually and it became sunny and hot during the day. A ridge of high pressure over southeastern China brought mainly fine and hot weather to the territory for the next two days.

    Affected by a broad trough of low pressure over the South China Sea, local weather turned mainly cloudy with some showers on 15 July. It became sunny and very hot on the following two days when a ridge of high pressure prevailed over the south China coastal areas.

    On 16 July, Molave intensified into a tropical storm and tracked northwestwards over the western North Pacific to the east of the Philippines. It further intensified into a severe tropical storm while crossing the Luzon Strait on 17 July and became a typhoon the next day after entering the South China Sea. The subsidence air mass ahead of Molave and the northerly winds associated with the typhoon brought very hot weather to Hong Kong in the afternoon of 18 July. The temperature recorded at the Hong Kong Observatory rose to a maximum of 34.3 degrees on that day, the highest in the month. With Molave moving closer to the coast of Guangdong, local winds strengthened gradually with squally showers in the evening of 18 July. Molave made landfall in the vicinity of Mirs Peninsula in the early hours of 19 July. Gale force winds with maximum gusts up to 148 kilometres per hour and heavy rain with squalls affected the territory during the period. Local winds subsided appreciably in the afternoon of 19 July as Molave weakened into a tropical depression and moved further inland over western Guangdong.

    A ridge of high pressure over southeastern China brought generally fine weather to Hong Kong from 20 to 22 July. Under the influence of a southwest monsoon, it was showery in the following four days. A trough of low pressure over southern China brought cloudy conditions with a few episodes of thunderstorms to the territory from 27 to 29 July. With the weakening of the trough, there were some sunny periods for the last two days of the month.

   Three tropical cyclones occurred in the western North Pacific and the South China Sea 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.