The Weather of July 1999

    July was warmer than normal. The mean temperature of 29.2 degrees ranked the sixth highest for the month and the mean minimum temperature of 27.2 degrees was the fifth highest for July. On the other hand, it was the cloudiest July with the mean amount of cloud reaching 82 per cent. The month was characterized by showery weather and there were only four days on which no rainfall was recorded. However, the total rainfall amounted to 203.8 millimetres only, 119.7 millimetres below the normal figure. The accumulated rainfall of 784.0 millimetres since 1 January was about 40 per cent below the normal figure. The approach of a tropical storm necessitated the hoisting of the Strong Wind Signal No. 3 on 26 July. The Amber Rainstorm Warning Signal was issued on two occasions.

    The weather was sunny apart from a few showers during the first two days of the month. It became cloudier on 3 July and showery activity persisted the next few days. It became thundery with heavy and squally showers on the morning of 8 July. Temperatures dropped to 23.8 degrees in heavy shower, the lowest in the month. Heavy and thundery showers persisted the next day especially in Sha Tin and Sai Kung but it became brighter in the afternoon. Sunny periods developed on 10 July although there were still one or two isolated showers.

    Generally fine weather prevailed on 11 and 12 July. A trough of low pressure in south China brought unsettled weather to the coast and heavy thunderstorms affected Hong Kong early on 13 July. It remained cloudy with a few showers the next few days but there were also sunny periods.

    Showery activities weakened on 18 July and the weather turned mainly sunny the next day. The fine weather persisted the next few days until thundery showers occurred again on 22 and 23 July. However, sunny conditions on 24 July brought the temperature up to 33.7 degrees in the afternoon, the highest in the month.

    A tropical depression formed over the northern part of the South China Sea on 25 July. Winds locally freshened from the east but the weather remained fine during the day. Squally showers began to affect Hong Kong in the evening becoming heavier and more frequent the next day as the tropical depression moved closer to Hong Kong and intensified into a tropical storm. Strong winds affected Hong Kong on 27 July. Winds subsided in the afternoon as the tropical storm moved away northeastwards. The weather remained mainly cloudy to overcast with light showers during the day.

    Hong Kong came under the influence of a southwesterly airstream on 28 July. The weather became fine with long sunny periods the next day as winds turned to easterly. Fine weather persisted until the last day of the month when some isolated showers returned.

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

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