Report on Super Typhoon Saola (2309)
Super Typhoon Saola (2309)
23 August – 3 September 2023
Saola was the third tropical cyclone affecting Hong Kong in 2023. Saola necessitated the issuance of the Hurricane Signal No. 10 again since Super Typhoon Mangkhut hitting Hong Kong in 2018. During the period of tropical cyclone warning signal No. 8 or above was in force, the maximum sustained wind near the centre of Saola was 210 km/h, breaking the previous record of 205 km/h set by Super Typhoon Hope in 1979 and setting the highest record since records began in 1946.
Saola formed as a tropical depression over the western North Pacific about 670 km southeast of Gaoxiong on the night of 23 August and moved slowly at first. It then made an anti-clockwise loop over the seas east of Luzon and intensified rapidly in the following five days. Saola intensified into a super typhoon on the night of 26 August. Saola weakened from super typhoon into a severe typhoon twice in the following three days, but intensified into a super typhoon again on the evening of 29 August and tracked west-northwestwards across Luzon Strait. Saola attained its peak intensity with an estimated maximum sustained wind of 230 km/h near its centre in the small hours of 30 August. Saola maintained this intensity and entered the South China Sea later that day, making it the second strongest tropical cyclone in the South China Sea since the Observatory’s records began in 1950, just after Super Typhoon Rammasun in 2014. It edged closer to the coast of Guangdong gradually while maintaining super typhoon intensity on the next day. Saola turned to move westwards across the coastal waters of Guangdong on 1 September. It weakened rapidly on 2 September and made landfall near Yangjiang of Guangdong in the afternoon. Saola continued to move across the coast of western Guangdong afterwards and weakened into a tropical depression progressively. Saola entered Beibu Wan on the morning of 3 September and finally weakened into an area of low pressure that night.
According to press reports, Saola brought torrential rain and squalls to the northern part of the Philippines, causing 2 deaths, 3 injures and 2 missing. More than 1.16 million people were affected, more than 7 800 houses were damaged and economic loss exceeded PHP 2.4 billion. Under the influence of the outer rainbands of Saola, there were 60 reports of flooding in Taiwan. Around 200 people were displaced and electricity supply to more than 10 000 households was disrupted; whereas in Fujian, about 450 000 people were affected, 170 000 people were displaced, more than 140 houses were damaged and economic loss exceeded RMB 870 million. There were over 16 000 reports of fallen trees in Zhuhai. About 70 vehicles were damaged and economic loss was around RMB 60 million. In Shenzhen, a large tree fell under strong winds and hit a passing vehicle, killing one person and injuring two people.
The Standby Signal No. 1 was issued at 5:40 p.m. on 30 August, when Saola was about 630 km east-southeast of Hong Kong. Local winds were moderate to fresh northerlies that night and next morning. With Saola edging closer to the coast of Guangdong, the No. 3 Strong Wind Signal was issued at 3:40 p.m. on 31 August, when Saola was about 380 km east-southeast of Hong Kong. Winds over Hong Kong strengthened overnight, with strong northerlies on high ground.
Since Saola was expected to come rather close to the Pearl River Estuary with severe typhoon to super typhoon intensity and posed threat to the territory later on 1 September, the No. 8 Northwest Gale or Storm Signal was issued at 2:40 a.m. on 1 September when Saola was about 280 km east-southeast of Hong Kong. As the circulation of Saola was compact, local winds strengthened rapidly later during the day, with gale force north to northwesterlies over many places and reaching storm force offshore and on high ground. Saola continued to approach Hong Kong with super typhoon intensity. The Increasing Gale or Storm Signal No. 9 was issued at 6:20 p.m. on 1 September when Saola was about 80 km east-southeast of the Observatory Headquarters. Local winds strengthened significantly in the evening, with gale to storm force east to northeasterlies generally over the territory and reaching hurricane force on high ground. Since the eyewall of Saola and its associated destructive hurricane force winds were expected to lash Hong Kong directly, the Hurricane Signal No. 10 was issued at 8:15 p.m. when Saola was about 50 km southeast of the Observatory Headquarters. Many places of the territory were affected by storm force winds at night; whereas southern part of the territory and high ground were persistently battered by hurricane force winds. Saola came closest to Hong Kong at around 9 p.m. when its centre was located at about 40 km to the south-southeast of the Observatory Headquarters.
With Saola skirting past south of Hong Kong, local winds veered to east to southeasterlies gradually. Saola then weakened and departed from Hong Kong gradually. When hurricane force winds no longer affected the territory, the No. 8 Southeast Gale or Storm Signal was issued at 3:40 a.m. on 2 September to replace the Hurricane Signal No. 10. Local winds continued to subside during the day. The No. 3 Strong Wind Signal was issued at 4:20 p.m. on 2 September, followed by the issuance of No. 1 Standby Signal at 8:20 p.m. With Saola further departing from Hong Kong, all tropical cyclone warning signals were cancelled at 11:40 p.m.
Government Flying Service dispatched a fixed-wing aircraft to conduct surveillance near the centre of Saola on the morning of 1 September. The photo taken from the aircraft showed that Saola was a mature tropical cyclone with a clear eye and well-defined eyewalls. Radar imagery at that time also showed that Saola had a double eyewall structure. While Saola approached Hong Kong later that day, its inner eyewall shrunk gradually due to eyewall replacement. When Saola passed south of Hong Kong on the night of 1 September, radar imagery (Figure 6c) depicted that its circulation was rather compact, with the strongest winds concentrating at only about 10-15 kilometers away from the centre.
The storm to hurricane force winds of Saola impacted many places in Hong Kong on 1 – 2 September. Maximum hourly mean winds of 153, 133 and 130 km/h and gusts of 183, 189 and 176 km/h were recorded at Waglan Island, Ngong Ping and Cheung Chau Beach respectively. During the passage of Saola, the overall wind strength in Hong Kong was similar to that of Hato in 2017, but relatively weaker than that of Mangkhut in 2018 (Table 2).
The storm surge induced by Saola resulted in flooding in some low-lying coastal areas of Hong Kong, including Sha Tin, Tai Po, and Tai O. A maximum sea level (above chart datum) of 3.41 m was recorded at Tsim Bei Tsui and a maximum storm surge (above astronomical tide) of 1.48 m was recorded at Tai Po Kau. The water level sensor at Sai Kung recorded about 4.5 mCD at midnight on 1 September. The lowest instantaneous mean sea-level pressures recorded at some selected stations are as follows:
| Station | Lowest instantaneous mean sea-level pressure (hPa) | Date/Month | Time |
|---|---|---|---|
| Hong Kong Observatory Headquarters | 986.7 | 1/9 | 9:45 p.m. |
| Hong Kong International Airport | 988.4 | 1/9 | 10:58 p.m. |
| Cheung Chau * | 982.8 | 1/9 | 10:24 p.m. |
| King’s Park | 986.9 | 1/9 | 9:24 p.m. |
| Lau Fau Shan | 989.9 | 1/9 | 8:41 p.m. |
| Peng Chau | 986.3 | 1/9 | 9:53 p.m. |
| Sha Tin | 988.9 | 1/9 | 8:27 p.m. |
| Sheung Shui | 991.5 | 1/9 | 7:36 p.m. |
| Ta Kwu Ling | 991.2 | 1/9 | 8:30 p.m. |
| Tai Po | 991.5 | 1/9 | 7:49 p.m. |
| Waglan Island | 979.1 | 1/9 | 8:48 p.m. |
Locally, it was hot and dry with sunny periods during the day on 30 and 31 August. Under the influence of the circulation of Saola, the local weather deteriorated rapidly with squally heavy showers later on 1 September. On 1 – 2 September, more than 150 millimetres of rainfall were recorded over most parts of the territory and rainfall even exceeded 250 millimetres over Central and Western, Wan Chai and Tsuen Wan Districts.
In Hong Kong, more than 86 people were injured. There were also over 3,000 reports of fallen trees, 21 reports of flooding and 7 reports of landslides during the passage of Saola. There were also about 40 reports of damaged scaffolding, signboards and windows. Power supply was temporarily interrupted in some places. 460 flights were cancelled at the Hong Kong International Airport.
During the passage of Saola, many road sections in Hong Kong needed to be closed due to fallen trees, falling objects, collapsed scaffoldings or flooding. A scaffolding collapsed on Portland Street in Mangkok, blocking two traffic lanes. More than ten solar panels on the roof of a building in Lei Cheng Uk Estate were blown onto the roads by strong winds. A glass window of a building in Tseung Kwan O InnoPark was loosened due to strong winds and fell onto the streets. The cycle track and pedestrian subway next to the Shing Mun River in Sha Tin were flooded. A tree fell in Diamond Hill, bending a lamppost and hitting a taxi. A glass curtain wall of a hotel in Yau Ma Tei fell down and hit three nearby cars. A scaffolding collapsed in Ap Lei Chau, hitting a taxi and a light goods vehicle. A modular house on the roof of a building in Kennedy Town was blown down by strong winds and hit a truck.
* based on incomplete data