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Ambrose Li

Hong Kong has escaped relatively unscathed from Super Typhoon Yagi compared with past storms as the city has reported no landslides, only one flooding case, 79 incidents of fallen trees and no fatalities.
The reduced impact left some wondering whether the storm was as strong as originally forecast and how the city avoided the worst of the super typhoon.
The Post takes a look at the characteristics of Yagi, which passed by Hong Kong on Thursday and was departing on Friday, and what they tell us about future typhoons.
1. Why did Hong Kong escape severe damage?
The distance between the city and Yagi played an important role in lessening its impact.
Former Observatory assistant director Leung Wing-mo said the storm did not seriously affect the city because it was about 400km (249 miles) away, although some “typical” conditions were observed such as strong gusts and occasional heavy showers.
Yagi moved at a slower speed – around 15km/h (9.3mph) – compared with the usual 20km/h, according to Leung. Easterly and south-easterly winds affected Hong Kong mostly in places such as Cheung Chau, other southern parts of the city and areas on higher ground, such as Ngong Ping on Lantau Island.
“There was also not much rain, because the typhoon really was quite far away,” Leung said. “Typically, the rain bands and cloud flows are usually several hundred kilometres [wide].”
Leung said Hong Kong could still experience strong gusts and occasional squally showers from the periphery of the super typhoon’s rain bands even as it moved away, but severe flooding was unlikely to occur.


2. Do low levels of damage mean Yagi was weak?
Not necessarily.
Leung explained a super typhoon was defined by the highest wind speed near the eye of the storm.
He added the level of damage also hinged on factors such as the distance of the typhoon from the city, even though the impact could be positively correlated to wind speeds.
Another factor is the presence of heavy rain, which usually brings sudden strong gusts.
“If we examine the satellite images of Yagi, we could in fact see a lot of rain bands,” Leung said. “Because Yagi is a super typhoon, when it lands in Hainan, the Leizhou Peninsula and Guangxi, it will be very destructive,” he said.




3. Why was the T8 forecast so early?
The Observatory gave advance notice of more than six hours over its issuing of the No 8 typhoon warning, one of the earliest in recent years. Leung said this was due to Yagi’s route being quite easy to predict.
“The Observatory relies on computerised numerical modelling to produce forecasts, involving computerised calculations and artificial intelligence models, which matched results from other major forecasting centres in the world,” he said.
He said Yagi had relatively simple steering currents, making it easier to track, while those of other major typhoons such as Saola and Koinu were more complicated.

4. Can we expect more early warnings in future?
Leung said the six-hour notice was the earliest possible warning, and the public should not expect similar time frames in the future.
“The movement of typhoons can be quite unpredictable. Yagi was quite ‘well-behaved’ by consistently heading westwards and northwestwards, meaning it was easier to understand its movement with the help of technology,” he said.
“How Yagi was dealt with was really the most [the Observatory] could do,” he said. “The typhoon signals themselves are a forecast, so a warning would be a forecast of a forecast. It would be impossible to infinitely extend this forecast.”
Leung said that while this could give people a head start to make relevant preparations, there would also be a higher likelihood of false alarms if the forecast was announced too early. Instead, authorities would need to strike a balance.
He said the Government Flying Service could not be called on to collect data from inside of the typhoon every time, as it did for Yagi, to help understand the storm better.
Hong Kong and operators of other weather agencies usually took reference from the world’s largest computer model, although Hong Kong also used its own in conjunction with other tools, he added.
“On the whole, our forecasts are among the top in the world,” he said.


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Super Typhoon Yagi: Hong Kong back in business after trees toppled, 9 hurt and flights axed

Super Typhoon Yagi

How did Hong Kong escape worst of ‘well-behaved’ Super Typhoon Yagi?

The Observatory gave advance warning of more than six hours over its issuing of the No 8 typhoon warning, one of the earliest in recent years. Photo: Dickson Lee

Residents watch the waves crash at the Heng Fa Chuen Promenade. Photo: Elson Li

What makes Yagi a ‘super typhoon’ and what should Hongkongers expect?

Hong Kong’s Central district on Thursday evening. Photo: Eugene Lee

Saola uprooted hundreds of trees in Hong Kong last year. Photo: Dickson Lee

Leung Wing-mo Photo: Roy Issa

What you need to know about Hong Kong MTR, taxi and ferry services during Super Typhoon Yagi

The Airport Authority said a total of 38 flights were cancelled on Thursday due to Super Typhoon Yagi. Photo: Sam Tsang

Super Typhoon Yagi: 38 flights cancelled in Hong Kong on Thursday as storm approaches

Among the most affected airlines are Cathay Pacific Airways budget carrier HK Express, Greater Bay Airlines and Hong Kong Airlines. Photo: Sam Tsang

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Storm battered city with strong gusts and occasional heavy showers, but distance played a part in easing the impact.


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Explainer | How did Hong Kong escape worst of ‘well-behaved’ Super Typhoon Yagi?

Storm battered city with strong gusts and occasional heavy showers, but distance played a part in easing the impact.

1. Why did Hong Kong escape severe damage?