TROPICAL CYCLONES IN 2013

Krosa was the seventh tropical cyclone necessitating the issuance of tropical cyclone warning signals by the Hong Kong Observatory in 2013. It was also the first tropical cyclone that requiring warning signals in Hong Kong in November since 2006.

Krosa formed as a tropical depression over the western North Pacific about 1 580 km east of Manila on 29 October. Moving generally west to west- northwestwards, it intensified gradually into a severe tropical storm the following day. Krosa intensified further into a typhoon on 31 October and crossed the northern tip of Luzon, where sustained wind of 108 km/h was reported at Aparri at 8 p.m. Krosa entered the northern part of the South China Sea the following day. It became slow moving and intensified into a severe typhoon over the northern part of the South China Sea on 2 November, reaching its peak intensity with estimated sustained winds of 165 km/h near its centre. Even though the circulation of Krosa was relatively small, it was rather compact in organisation, with an eye clearly visible on satellite imageries. Krosa weakened into a typhoon in the early hours on 3 November. As a replenishment of the northeast monsoon extended gradually towards the northern part of the South China Sea, Krosa turned southwestwards and weakened into a tropical storm that evening. It continued to weaken into a tropical depression the following day and dissipated over the central part of the South China Sea near the coastal areas of central Vietnam at night. According to press reports, three people were killed, two people were reported missing and more than 17 000 houses were damaged in the Philippines during the passage of Krosa.

The Hong Kong Observatory issued the Standby Signal No. 1 at 3:20 p.m. on 1 November when Krosa was about 520 km southeast of the territory. Local winds were moderate northeasterlies that day, occasionally strong on high ground at night. The northeasterlies freshened in the next couple of days, becoming strong offshore and on high ground. At the Hong Kong Observatory Headquarters, the lowest instantaneous mean sea-level pressure of 1010.2 hPa was recorded at 2:06 p.m. on 2 November, when Krosa was about 290 km to the south-southeast. Krosa moved slowly and weakened over the northern part of the South China Sea passing to the south of Hong Kong on 3 November. It was closest to the territory around 2 p.m. that day when it was about 220 km to the south. As Krosa moved southwestwards away from Hong Kong and continued to weaken, all signals were cancelled at 10:50 p.m.

During the passage of Krosa, maximum hourly mean wind of 51 km/h was recorded at Waglan Island, while maximum gust of 68 km/h was recorded at Green Island. A maximum sea level of 2.88 m (above chart datum) was recorded at Tsim Bei Tsui, while a maximum storm surge of 0.47 m was recorded at Tai Po Kau.

No significant damage was reported in Hong Kong during the passage of Krosa. The weather was fine and dry with abundant sunshine during the day on 1 November. Affected by the rainbands of Krosa, local weather became cloudy with a few showers over the next two days. Only several millimetres of rainfall were recorded in parts of the territory during the period.

Information on the maximum wind, daily rainfall and maximum sea level reached in Hong Kong during the passage of Krosa is given in Tables 3.7.1 - 3.7.3 respectively. Figures 3.7.1 - 3.7.3 show respectively the track of Krosa, the rainfall distribution for Hong Kong, a satellite imagery of Krosa.