Typhoon Koinu, known in the Philippines as Typhoon Jenny, was a strong and damaging

tropical cyclone A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...

that made landfall on the southern tip of

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

and affected

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

in early October 2023. Koinu (子犬), a replacement name for Tembin which means ''

puppy A puppy is a Juvenile (organism), juvenile dog, generally one less than 12-18 months old. Puppies are markedly underdeveloped and dependent on their mothers at birth (displaying ''altriciality''), but healthy puppies grow quickly and begi ...

'' or ''

Canis Minor Canis Minor is a small constellation in the Celestial sphere, northern celestial hemisphere. In the second century, it was included as an Asterism (astronomy), asterism, or pattern, of two stars in Ptolemy's 48 constellations, and it is counte ...

'' in Japanese, was the fourteenth

named storm Tropical cyclones and subtropical cyclones are named by various warning centers to simplify communication between forecasters and the general public regarding forecasts, watches and warnings. The names are intended to reduce confusion in the ...

and ninth typhoon of the inactive

2023 Pacific typhoon season The 2023 Pacific typhoon season was the fourth and final consecutive below-average season and became the third-most inactive typhoon season on record in terms of named storms, with just 17 named storms developing, only ahead of 2010 Pacific typho ...

. Koinu originated from an area of low pressure near

Guam Guam ( ; ) is an island that is an Territories of the United States, organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, Guam, Hagåtña, and the most ...

that generally moved westward into the Philippine Sea, where it was upgraded into a depression. Koinu later underwent rapid intensification and became a Category 3-equivalent typhoon. The storm then weakened before intensifying to attain its peak intensity as a category 4-equivalent typhoon. Koinu passed close by

Lanyu Orchid Island, known as Pongso no Tao by the indigenous inhabitants, is a volcanic island located off the southeastern coast of Taiwan, the island and the nearby are governed by Taiwan as in Taitung County, which is one of the county's two ...

then made landfall over Hengchun, Taiwan.

Meteorological history

On September 27, a low-pressure area formed near Guam, with the JTWC indicating the potential development of a tropical cyclone. It moved westward into the Philippine Sea until it entered the Philippine Area of Responsibility, where it was later upgraded into a tropical depression and gained the name ''Jenny'' by the PAGASA. A

Tropical Cyclone Formation Alert A Tropical Cyclone Formation Alert (TCFA) is a bulletin released by the U.S. Navy-operated Joint Typhoon Warning Center in Honolulu, Hawaii or the Fleet Weather Center in Norfolk, Virginia, warning of the possibility of a tropical cyclone formi ...

was then issued for Jenny as it began to show signs of further organization. Hours later, JTWC gave its identifier ''14W'' at 13:00 UTC (21:00 PHT). On September 28, JMA upgraded 14W into a tropical storm and attained the name ''Koinu'', which replaced the name Tembin. PAGASA later followed suit at their 5 AM PHT bulletin, also upgrading Jenny into a tropical storm; JTWC followed thereafter. Koinu moved west northwestward in the

Philippine Sea The Philippine Sea is a List of seas#Marginal seas by ocean, marginal sea of the Pacific Ocean, Western Pacific Ocean east of the list of islands of the Philippines, Philippine Archipelago (hence the name) and the List of seas#Largest seas ...

whilst having its low-level circulation exposed due to

wind shear Wind shear (; also written windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical ...

. Koinu then later organized further, and by the next day, the JMA upgraded Koinu into a severe tropical storm. As usual, the PAGASA followed suit a few hours later. Koinu later gradually intensified into a Category 1 typhoon by the JTWC. The other agencies also followed suit in upgrading Koinu into a typhoon as an eye began to form. Koinu then began a period of

rapid intensification Rapid intensification (RI) is any process wherein a tropical cyclone strengthens very dramatically in a short period of time. Tropical cyclone forecasting agencies utilize differing thresholds for designating rapid intensification events, th ...

by the evening of October 1 into the early morning hours, intensifying to become a low-end Category 4 typhoon whilst it developed a clear eye as it moved east of

Cagayan Cagayan ( ), officially the Province of Cagayan (; ; ; isnag language, Isnag: ''Provinsia nga Cagayan''; ivatan language, Ivatan: ''Provinsiya nu Cagayan''; ; ), is a Provinces of the Philippines, province in the Philippines located in the Cag ...

before weakening slightly. Koinu weakened to Category 2 strength yet rebounded its intensity and reached Category 4 again whilst nearing

and moving west northwestward. Koinu passed dangerously close to

, and making its first landfall on mainland

Hengchun Hengchun is a Township (Taiwan), township located on the southern tip of the Hengchun Peninsula in Pingtung County, Taiwan. It is the southernmost township in Taiwan. Hengchun is also the only urban township in the southern part of Pingtung Coun ...

, Taiwan, later weakening into a Category 3 storm as it did so. Koinu then weakened into a Category 1 after slamming into Taiwan and later exited the PAR into the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan island, Taiwan and northwestern Philippines (mainly Luz ...

. Contrary to forecasts, Koinu unexpectedly restrengthened back into a Category 2, reforming a clear visible eye surrounded by a powerful eyewall. Koinu further intensified, regaining Category 3 status east of

Guangdong ) means "wide" or "vast", and has been associated with the region since the creation of Guang Prefecture in AD 226. The name "''Guang''" ultimately came from Guangxin ( zh, labels=no, first=t, t= , s=广信), an outpost established in Han dynasty ...

. After re-intensifying, Koinu weakened again for the last time, as it started to move west-northwestward. Dry air intrusion and land interaction continued to weaken the system into a tropical storm on October 9. Afterwards, it weakened to a tropical depression before reaching the

Leizhou Peninsula The Leizhou Peninsula, alternately romanized as the Luichow Peninsula, is a peninsula in the southernmost part of Guangdong province in South China. As of 2015, the population of the peninsula was 5,694,245. The largest city by population and ...

into the

Gulf of Tonkin The Gulf of Tonkin is a gulf at the northwestern portion of the South China Sea, located off the coasts of Tonkin ( northern Vietnam) and South China. It has a total surface area of . It is defined in the west and northwest by the northern co ...

. Both agencies ceased their advisories as Koinu weakened into a remnant low on October 10.

Preparations and impact

Philippines

As Typhoon Koinu (known as Jenny in the Philippines) approached the Northern Philippines including Extreme Northern Luzon, the

PAGASA The Philippine Atmospheric, Geophysical and Astronomical Services Administration (, abbreviated as PAGASA , which means "hope" as in the Tagalog language, Tagalog word ''pag-asa'') is the National Meteorological and Hydrological Services (NMHS ...

began issuing warnings for parts of

Northern Luzon Luzon ( , ) is the largest and most populous List of islands in the Philippines, island in the Philippines. Located in the northern portion of the List of islands of the Philippines, Philippine archipelago, it is the economic and political ce ...

, and a few days later, Signal #3 was raised on

Itbayat, Batanes Itbayat, officially the Municipality of Itbayat, (; Ilocano: ''Ili ti Itbayat''; ), is a municipality in the province of Batanes, Philippines. In the 2020 census, it had a population of 3,128 people. Itbayat is the country's northernmost muni ...

as the typhoon brought showers and gusty winds to the islands. As Jenny moved further away and weakened, the rains and winds started to subside, however, locals were still warned that the storm may still trigger moderate to rough seas in the areas affected.

Taiwan

Taiwanese authorities issued weather warnings in preparation of strong gusts and heavy rain hitting the island's southeast. According to news sources, flights were canceled, schools and businesses were closed, and fishermen secured their boats. While the storm is likely to bring the most rain to hilly and sparsely inhabited areas, it will also affect the large port city of Kaohsiung. As Koinu made landfall, it brought record-breaking winds and rains. A weather station on

Orchid Island Orchid Island, known as Pongso no Tao by the indigenous inhabitants, is a volcanic island located off the southeastern coast of Taiwan, the island and the nearby are governed by Taiwan as in Taitung County, which is one of the county's two ...

recorded sustained winds of at 9:40 p.m. and gusts of 13 minutes later, both representing record-highs since record-keeping began in 1897. Many trees fell down on roads and damaged infrastructure. A landslide occurred on Provincial Highway No. 9 in

Pingtung County Pingtung () is a County (Taiwan), county located in southern Taiwan. It has a warm tropical monsoon climate and is known for its agriculture and tourism. Kenting National Park, Taiwan's oldest national park, is located in the county. The county ...

forcing vehicles to drive on the same lane, while 2 roads in

Taitung County Taitung () is the third largest county in Taiwan, located primarily on the island's southeastern coast and also including Green Island, Orchid Island and Lesser Orchid Island. The seat is located in Taitung City. Name While its name means "East ...

, Provincial Highway 20 in Haiduan Township and Provincial Highway 23 in Donghe Township were blocked. Agricultural losses in Taiwan were about NT$344.56 million (US$10.72 million), according to the Ministry of Agriculture (MOA). The five administrative areas that sustained the greatest losses were

Yunlin Yunlin is a county in western Taiwan. Yunlin County borders the Taiwan Strait to the west, Nantou County to the east, Changhua County to the north at the Zhuoshui River, and Chiayi County to the south at the Beigang River. It has a population ...

Changhua Changhua (Hokkien Pe̍h-ōe-jī, POJ: ''Chiong-hòa'' or ''Chiang-hòa''), officially known as Changhua City, is a county-administered city and the county seat of Changhua County in Taiwan. For many centuries the site was home to a settlement of ...

Taichung Taichung (, Wade–Giles: '), officially Taichung City, is a special municipality (Taiwan), special municipality in central Taiwan. Taichung is Taiwan's second-largest city, with more than 2.85 million residents, making it the largest city in Ce ...

Chiayi Chiayi (,), officially known as Chiayi City, is a Provincial city (Taiwan), city located in Chianan Plain in Regions of Taiwan, southwestern Taiwan, surrounded by Chiayi County with a population of 263,188 inhabitants as of January 2023. The H ...

, and

Tainan Tainan (), officially Tainan City, is a Special municipality (Taiwan), special municipality in southern Taiwan, facing the Taiwan Strait on its western coast. Tainan is the oldest city on the island and commonly called the "Taiwan Prefecture, ...

. Around 9,762 hectares of crops were damaged. Peanuts were the crop that sustained the largest losses, while chickens and pigs were the largest livestock and poultry losses.

Hong Kong

As Typhoon Koinu neared Hong Kong, the

Hong Kong Observatory The Hong Kong Observatory is a weather forecast agency of the government of Hong Kong. The Observatory forecasts the weather and issues warnings on weather-related hazards. It also monitors and makes assessments on radiation levels in Hong ...

(HKO) issued Increasing Storm Signal No. 9 at 19:00 (HKT) and weather warnings in preparations for heavy rainfall and strong winds ahead of the storm. The agency then considered if they would hoist their second Hurricane Signal No. 10 since Typhoon Saola if the storm passed further closely to Hong Kong. However, as Koinu moved away from Hong Kong and started weakening, the HKO did not need to issue the highest wind signal. The Increasing Storm Signal No. 9 was kept in force for 4 hours before lowered it down to Southwest Gale or Storm Signal No. 8.

References

External links

{{2023 Pacific typhoon season buttons Koinu 2023 in the Northern Mariana Islands 2023 in Guam 2023 in Hong Kong 2023 in Macau September 2023 in Oceania October 2023 in Oceania September 2023 in the United States October 2023 in the United States October 2023 in the Philippines October 2023 in Taiwan October 2023 in China 2023 natural disasters in the United States 2023 disasters in the Philippines 2023 disasters in Taiwan 2023 disasters in China Typhoons in the Philippines Typhoons in Taiwan Typhoons in China Typhoons in the Northern Mariana Islands Typhoons in Guam Typhoons in Hong Kong Typhoons in Macau