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Category 4 Typhoon Saola batters Hong Kong » Yale Climate Connections


Historic Typhoon Saola gave Hong Kong a tremendous pounding on Friday evening local time as the ferocious 130-mph sustained winds of its northern eyewall raked the city. Saola (named after one of the world’s rarest large mammals, a forest-dwelling bovine native to the Annamite Range in Vietnam and Laos) triggered the issuance of a rare “Signal 10” advisory for Hong Kong from the Hong Kong Observatory (HKO), reserved for the most extreme storms, for the first time since 2018.

At 8 a.m. EDT Friday, the center of Saola was located just 18 miles southeast of Hong Kong, moving west at 10 mph, according to the Joint Typhoon Warning Center (JTWC). This relatively slow motion allowed the typhoon to subject Hong Kong to an extended pounding by the winds of its northern eyewall, where the strongest winds were. The eye of the storm passed over the Dangan Island Weather Station, located about 15 miles south of Hong Kong, where sustained 2-minute winds of 115 mph, gusting to 138 mph, were observed, along with a lowest pressure of 968 mb. The eye also passed over Miaoan Island, which recorded sustained winds of 107 mph, gusting to 139 mph, and a lowest pressure reading of 959 mb. At 11 p.m. local time, HKO reported sustained winds at three measurement sites (Waglan Island, Cheung Chau Beach and Green Island) of 87-99 mph, with gusts of 109-113 mph. Winds of this magnitude are likely to cause very heavy damage and pile up a near-record storm surge.

The Hong Kong observatory warned at 11 p.m. Friday evening local time, when Saola was at its closest, “At present, the water level at Tolo Harbour rises above 3 metres. The maximum water level is expected to be 5 to 6 metres above chart datum before midnight, and may reach a historical record since the availability of instrumental data in that region. There will be serious flooding in low-lying coastal areas such as Shatin, Tai Po, Sha Tau Kok, Sai Kung, etc. The maximum water level at Victoria Harbour will be some 3 metres above chart datum. The water level at Tai O will also rise to some 3 metres above chart datum around 9 a.m. tomorrow morning (2 September).”

Fortunately, Hong Kong is not especially vulnerable to storm surge, since it has few low-lying areas. However, neighboring Guangzhou, China, with a metro-area population of 25 million, is in the strong right front quadrant of the typhoon, and may experience a significant storm surge. Guangzhou is the #1 most vulnerable city on the planet to damage from sea level rise and coastal flooding, according to a World Bank report.

Hong Kong typhoon history

According to the JTWC database, Saola is the second-strongest typhoon on record to pass so close to Hong Kong (Figure 1). The other was catastrophic Typhoon Ruby of 1964, which had 140 mph winds as it passed just to the south. Ruby killed 686 people in Hong Kong and China.

The most recent typhoon to pass within 100 miles of Hong Kong – the most recent one to earn a Signal 10 warning – was Mangkut of 2018, which passed about 70 miles to the south as a category 1 storm with 90 mph winds. No deaths were reported from Mangkut, and damage was $900 million (2022 USD). In 2017, category 2 Typhoon Hato (also a Signal 10 storm) passed just 40 miles south of Hong Kong, killing eight and doing $4.2 billion in damage (2022 USD).

The South China Morning Post has an excellent summary of the history of typhoons in Hong Hong though the year 2013, and an impressive YouTube video showing scenes from Mangkhut in 2018.

Figure 1. Tracks of all category 3 and stronger typhoons to pass within 100 miles of Hong Kong, 1945-2022, according to the Joint Typhoon Warning Center. (Image credit: NOAA)

The top ten most damaging typhoons in Asian history

Saola has some serious destruction it must wreak if it is to rank as one of the top 10 most expensive typhoons on record in Asia. According to EM-DAT, the most expensive typhoons on record (in 2022 dollars adjusted for inflation) are:

1) $21 billion, Typhoon Mirelle, Japan, 1991
2) $19 billion, Typhoon Hagibis, Japan, 2019
3) $14 billion, Typhoon Saomai, Japan, 2000
4) $14 billion, Typhoon Jebi, Japan, 2018
5) $13 billion, Typhoon Songda, Japan, 2004
6) $12 billion, Typhoon Haiyan, Philippines, 2013
7) $11 billion, Typhoon Lekina, China, 2019
8) $10 billion, Typhoon Faxai, Japan, 2019
9) $10 billion, Typhoon Praparoon, Korea, 2000
10) $9 billion, Typhoon Flo, Japan, 1990

This list leaves out what was possibly the most destructive Chinese typhoon of all time, Typhoon Nina of 1975. Nina stalled out and dumped prodigious rains for two days in the Ru River drainage basin upstream of the Banqiao Dam, leading to the dam’s collapse and the loss of 171,000 lives, with an area 34 miles long and 8 miles wide wiped out. The disaster was not disclosed by China until the mid-1990s.

Typhoon Haikui threatens Taiwan

Typhoon Haikui, which was a category 1 storm with 85 mph winds at 8 a.m. EDT Friday, is predicted to hit Taiwan Sunday morning (U.S. EDT), most likely as a Category 2 storm.

A swarm of Atlantic systems: Gert, Franklin, Idalia, and Jose (and a likely Katia-to-be)

It’s not every day there are four named systems in the Atlantic, even at peak season. It’s even more unusual to have such a quartet packed together into a Northwest Atlantic cluster like they were on Friday morning. One reason the group can coexist is that they’re of variegated sizes and life stages: in fact, each of these four had a different official designation (hurricane, tropical storm, tropical depression, and post-tropical cyclone). The interaction among these systems makes for an unusually complex forecast, but none of the group is expected to pose a major threat to any land areas. Here’s a recap, in alphabetic order:

Figure 2. Post-Tropical Cyclone Idalia, Hurricane Franklin, Tropical Storm Jose, and Tropical Depression Gert at 1600Z (noon EDT) Friday, September 1, 2023. (Image credit: RAMMB/CIRA/CSU)
  • Resilient Hurricane Franklin, a Category 4 storm earlier this week, was still a minimal Category 1 storm at 11 a.m. EDT Friday, located almost 700 miles northeast of Bermuda with top sustained winds of 75 mph. While Franklin still had robust shower and thunderstorm activity (convection), it was taking on the comma shape more typical of mid-latitude storm systems. The National Hurricane Center (NHC) will likely designate Franklin post-tropical by Friday night as the storm races northeast and gradually weakens. Next week could see the remnants of Franklin angling north toward Greenland and Iceland, or heading more eastward toward western Europe.
  • Former Tropical Storm Gert has risen from a watery grave and is now Tropical Depression Gert, after 10 days of roaming the central Atlantic as a remnant/post-tropical cyclone. The National Hurricane Center (NHC) revived TD Gert at 5 a.m. EDT Friday after the system had gradually reorganized and developed a persistent core of strong showers and thunderstorms (convection) atop a circulation that had never completely dissipated. Fighting strong wind shear of 25-35 knots, Gert is drawing on unusually warm subtropical waters of 29-30 degrees Celsius (84-86 degrees Fahrenheit) and a moist midlevel atmosphere (relative humidity around 60-65 percent). As it rotates east and then north around Idalia, Gert may remain just organized enough to retain minimal tropical-storm status this weekend, but NHC predicts that Gert will be absorbed by Idalia around Monday.
  • Former Category 4 Hurricane Idalia is now Post-Tropical Cyclone Idalia, large but devoid of convection, attached to a mid-latitude front in the Northwest Atlantic, west of Bermuda. Light wind shear (less than 10 knots) was helping Idalia’s circulation to maintain its integrity and its peak sustained winds of 60 mph, despite the absence of convection. Idalia is angling east-southeast toward warmer waters, which raises uncertainty about its future. Should organized convection redevelop, Idalia could again become a tropical storm, or even a subtropical storm if it remains tangled in a frontal zone. The official forecast shows Idalia again a tropical storm starting on Saturday when it will be passing just south of Bermuda. Early next week, Idalia is likely to accelerate toward the northeast, but model ensembles show a wide range of potential tracks, some as far north as the Canadian Maritimes.

Idalia produced very few deaths or serious injuries in the United States (a couple of storm-related deaths have been confirmed, according to the Associated Press). However, because of its storm surge in multiple states and its torrential rains and flooding (see embedded tweet above), it will still likely be another costly multi-billion dollar disaster. Moody’s Analytics estimates that the financial toll from Idalia will likely run from $12 to $20 billion in damage and lost economic output. The latter is not typically included in damage estimates, so the final damage-only toll could be less. “Unlike other recent events, the bulk [of the cost] comes not from a handful of counties that were decimated but instead a large, multi-state area experiencing significant but not catastrophic damage,” Adam Kamins, director of regional economics at Moody’s Analytics, wrote in a report on Thursday. If damage from Idalia does reach $20 billion, it would rank as the 18th-costliest hurricane on record for the U.S. (Figure 2). It’s not out of the question that Idalia will end up being retired from the hurricane naming lists and joining the increasing crop of “I” names no longer being used.

Figure 2. U.S. weather disasters costing at least $20 billion since 1980, according to NOAA.
  • Compact Tropical Storm Jose has overperformed since it was named on Thursday, ginning up top sustained winds as high as 60 mph on Thursday night. However, Jose was rapidly devolving on Friday morning. Although top sustained winds remained 50 mph at 11 a.m. EDT Friday, Jose’s low-level center was racing northeastward into the orbit of Franklin, leaving Jose’s convection behind. It appears the storm will be fully absorbed by Franklin by Friday night or Saturday.
Figure 2. Post-Tropical Cyclone Idalia, Hurricane Franklin, Tropical Storm Jose, and Tropical Depression Gert at 1600Z (noon EDT) Friday, September 1, 2023. (Image credit: RAMMB/CIRA/CSU)
  • In the eastern tropical Atlantic, far away from the quartet above, Invest 94L was upgraded to Tropical Depression 12 at 11 a.m. EDT Friday. TD 12 was located almost 400 miles northwest of the Cabo Verde Islands with top sustained winds of 35 mph, moving northwest at about 8 mph. Convection around TD 12 was extensive but quite disorganized on Friday; some spin was evident on satellite. TD 12 has a reasonable chance of intensifying into a weak tropical storm by Saturday, as predicted by NHC, given light to moderate wind shear (5-15 knots), warm sea surface temperatures of 27-28°C (81-82°F), and a moist mid-level atmosphere (65-70% relative humidity). Later this weekend and into next week, increasing wind shear and a substantially drier atmosphere should cap 94L’s strength as it moves northwest over marginally warm waters. The next name on the Atlantic list is Katia.

Next tropical wave coming this weekend bears watching

The last system to discuss – but definitely not the least among them – is a tropical wave predicted to move off the coast of Africa on Saturday. This wave has been getting strong model support for development and is predicted to follow a more westerly track than most waves we’ve seen roll off Africa. This makes the wave a potential long-range threat to the Lesser Antilles, and one that residents of North America will also want to watch. The long-range fate of the wave will depend upon the complex interaction between Idalia, Franklin, Gert, and Jose, something very difficult to predict at present. One or more of these storms may be able to create a lane of low pressure over the central Atlantic pronounced enough to turn the wave northward far enough to recurve it out to sea.

Due to the Labor Day holiday weekend, we will be making limited updates and/or fresh posts until Tuesday.

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