The Weather of July 1998

    July 1998 was a hot month.  The mean minimum temperature of 27.1 degrees was the seventh highest on record for the month and the mean temperature of 29.0 degrees also ranked the ninth highest for the month.  With the absence of tropical cyclones in the vicinity, the mean pressure of 1 007.3 hectopascals was the sixth highest for July.  Hong Kong was also not affected by any tropical cyclones so far this year.  This is the first time in post-war years that no Tropical Cyclone Warning Signals were displayed in the first seven months of the year.

    The total rainfall of 267.2 millimetres in the month was 56.3 millimetres below the normal figure, but the cumulative rainfall since 1 January, 1 911.9 millimetres, was still 45 per cent more than the normal for the same period.  The Amber Rainstorm Warning Signals were issued on five occasions in the month.

    The first half of the month was mainly showery with the presence of troughs of low pressure over the northern part of the South China Sea, while the second half of the month saw the establishment of a ridge of high pressure over our region and the weather was sunny and hot.

    The weather was fine with long sunny periods during the first day of the month but showers developed in the evening.  As a trough of low pressure formed and persisted over the northern part of the South China Sea, it became cloudy with showers which were heavy and thundery at times during the next few days.  A worker was struck by lightning in Tai Po on 3 July. Temperatures dropped to 23.7 degrees in heavy showers on 4 July, the lowest in the month.

    The weather improved on 7 July with longer sunny periods though there were still isolated showers in the next couple of days.  It became fine and sunny on 10 July, but cloud amounts gradually increased the next day.  Showers returned on the evening of 12 July, becoming heavy and thundery the next day as another trough formed near the coast.

    The weather improved gradually as the trough dissipated and a ridge of high pressure became established over the south China coastal areas.  Starting from 15 July, the weather was generally fine, sunny and hot apart from a few isolated showers till the end of the month.  However there were some isolated heavy showers on 21 July and a few thunderstorms on 27 July.

    Temperatures rose to 33.3 degrees on 28 July, the highest so far this year. It was even hotter in the New Territories with a maximum temperature of 36.3 degrees recorded at Ta Kwu Ling on the last day of the month.

    Only one tropical cyclone occurred in the South China Sea and the western North Pacific in the month.

    During the month, a total of 9 aircraft was diverted due to adverse weather.