Tropical Storm Dianmu was a weak
tropical cyclone
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depen ...
that caused considerable damage over parts of
Mainland Southeast Asia during late-September 2021. The fifteenth
named storm of the
2021 Pacific typhoon season
The 2021 Pacific typhoon season was the second consecutive to have below-average tropical cyclone activity, with twenty-two named storms, and was the least active since 2011. Nine became typhoons, and five of those intensified into super typho ...
, Dianmu originated from an area of low-pressure situated in the South China Sea on September 21. Being first monitored by the
Joint Typhoon Warning Center
The Joint typhoon Warning Center (JTWC) is a joint United States Navy – United States Air Force command in Pearl Harbor, Hawaii. The JTWC is responsible for the issuing of tropical cyclone warnings in the North-West Pacific Ocean, South P ...
, the system rapidly consolidated to a tropical depression on September 22 as it continued to approach
Vietnam
Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...
before strengthening further to a weak tropical storm, with the
Japan Meteorological Agency
The , abbreviated JMA, is an agency of the Ministry of Land, Infrastructure, Transport and Tourism. It is charged with gathering and providing results for the public in Japan that are obtained from data based on daily scientific observation an ...
naming it as "Dianmu". Little intensification occurred before it made landfall on the country with winds of . It then rapidly weakened over land and dissipated on September 24 as a tropical cyclone.
Heavy rains resulted in severe flooding in Vietnam and Thailand, as well as affecting Laos during its lifespan. Many livestock and agricultural lands were also affected, along with over 300,000 people. 8 people were killed and 5 were missing due to Dianmu's onslaught. A short-lived storm, after it crossed into the
Mainland Southeast Asia, its remnants emerged into the
Bay of Bengal
The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line betwee ...
and affected the
West Bengal
West Bengal (, Bengali: ''Poshchim Bongo'', , abbr. WB) is a state in the eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabitants within an area of . West Bengal is the fou ...
.
Meteorological history
On September 21 at 21:00
UTC, the United States
Joint Typhoon Warning Center
The Joint typhoon Warning Center (JTWC) is a joint United States Navy – United States Air Force command in Pearl Harbor, Hawaii. The JTWC is responsible for the issuing of tropical cyclone warnings in the North-West Pacific Ocean, South P ...
(JTWC) started to monitor an area of low-pressure in the
South China Sea
The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Phi ...
, to the northwest of
Puerto Princesa,
Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
. At that time, infrared imagery revealed a
low-level circulation center
The eye is a region of mostly calm weather at the center of tropical cyclones. The eye of a storm is a roughly circular area, typically in diameter. It is surrounded by the ''eyewall'', a ring of towering thunderstorms where the most severe weat ...
being defined and organized with its
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the conve ...
onto its western semicircle. Environmental analysis on the area depicted a favorable path for
tropical cyclogenesis
Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tr ...
, with low
wind shear
Wind shear (or 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 or horizont ...
, good
outflow and warm
sea surface temperatures
Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air mas ...
. However, at that time, the agency only estimated the system's probability of development to “low” as forecast ensembles only indicated a slow formation of the storm in the next 24 hours until 09:30 UTC on the next day, when they raised it to “medium” and subsequently upgraded it to a tropical depression at 15:00 UTC that day.
However, the
Japan Meteorological Agency
The , abbreviated JMA, is an agency of the Ministry of Land, Infrastructure, Transport and Tourism. It is charged with gathering and providing results for the public in Japan that are obtained from data based on daily scientific observation an ...
did the same three hours later.
A rapidly organizing system, the depression was steered west-northwestward by the southern periphery of a low to mid-level
subtropical ridge to the north.
As it neared the coast of
Vietnam
Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...
, the JMA further upgraded the depression to a tropical storm, assigning it the name ''Dianmu'' from its naming lists at 06:00 UTC on September 23; the JTWC did the same three hours later based on microwave images and radar coverage. As Dianmu made landfall over the Vietnamese provinces of
Thua Thien Hue and
Quang Ngai on the early hours of September 24 with winds of , the JTWC issued its final bulletin on the storm as it weakened considerably over the country at 15:00 UTC, although it remained a tropical storm upon its final issuance. The JMA, meanwhile, downgraded Dianmu back to a tropical depression twelve hours later before it issued its final warning on the system as it dissipated as a remnant low at 12:00 UTC on September 24. However, its remnants crossed into the
Bay of Bengal
The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line betwee ...
, where it intensified to a low-pressure area before it moved inland for the second time over
West Bengal
West Bengal (, Bengali: ''Poshchim Bongo'', , abbr. WB) is a state in the eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabitants within an area of . West Bengal is the fou ...
.
Impacts
Dianmu and its resulting floods killed 8 individuals across Thailand and Vietnam while 5 were reported to have been missing. 73,938 families (369,690 individuals) were affected by the storm and heavy rainfall had caused flooding in these countries.
Vietnam
On September 23, Le Van Thanh, the National Steering Committee for Natural Disaster Prevention and Control (NSCNDPC) Deputy Prime Minister, conducted an online meeting with the leaders of People's Committee of various districts to discuss the storm's potential impacts. There, preparations discussed included the sending information to the remaining 28 ships in the waters off
Quang Binh to
Bình Thuận and the
Covid-19
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was identified in Wuhan, China, in December 2019. The disease quickly ...
testing of vessel crews and sheltering their boats. Evacuation of individuals in Quảng Nam were discussed, along with the advice of the People's Committee of the province to store food and important necessities for 7–10 days. The People's Committee of Da Nang also reminded its people to remain in their houses and not to venture outside while the storm is passing.
On a six-hour period of September 23, of rainfall was recorded at
Bình Sơn District in
Quảng Ngãi
Quảng Ngãi () is a city in central Vietnam. It serves as the capital city of Quảng Ngãi Province. Quảng Ngãi City borders Tư Nghĩa District to the south and west, Sơn Tịnh District to the northwest and Bình Sơn District to the ...
and on
Sơn Hà District in the same province. The system also likely spawned two tornados in the country, one in
Núi Thành District,
Quảng Nam Province on September 23 in which it caused roof and household damages, including a school. An individual was injured. The other one was in Duy Phước, which damaged another elementary school. Strong winds also uprooted trees and damaged houses in some coastal communities in Nui Thanh while the authorities in Tam Tien evacuated people that are located in damaged houses and other dangerous areas. Residential areas near the Tra Bong River and Quảng Ngãi were flooded while 7 houses collapsed as a result of the storm in Binh Dong, Binh Son district.
Ly Son Island suffered damages to 300 hectares of onions and garlic and 10 houses in a village there.
A 2,000-ton cargo ship collided with a fishing boat on the coast of
Bình Định Province
B, or b, is the second letter of the Latin-script alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is '' bee'' (pronounced ), plural ''bees''. It r ...
on September 24, leaving 2 fishermen missing out of the three of the latter which was rescued. The vessel was severely damaged following the accident. 2 more children drowned in Tuy Phuoc district, Binh Dinh after they slipped in a lake to collect bottles floating. Another fisherman was reported missing.
As of September 25, over 2,845 families (14,225 individuals) were affected by Dianmu, 2725 houses and 3,734 ha of agricultural crops and lands being damaged, 201 roads and 5 schools suffering significant destruction and 5,402 livestock being reported to have been killed.
Thailand
The influence of the remnants of Dianmu, that moved with the monsoon trough that persisted in Northeast and Central regions of the country caused heavy rainfall in its upper regions and 30 more areas in the said zones. of rain was reported in Tak Fa,
Nakhon Sawan Province and Phliu,
Chanthaburi Province at in a 24-hour period from September 23–24. 10 areas in the country also recorded an increase in water level of its rivers. The levels of dams and reservoirs in 11 locations were also critical. The authorities in the capital
Bangkok
Bangkok, officially known in Thai as Krung Thep Maha Nakhon and colloquially as Krung Thep, is the capital and most populous city of Thailand. The city occupies in the Chao Phraya River delta in central Thailand and has an estimated populati ...
installed water pumps and barriers to help subside floods. 71,093 households (355,465 persons) were affected with the flash floods.
The
Chao Phraya River in Bangkok also saw an increase in its water level due to rains. Thai servicemen gathered to fill sandbags to protect the
Wat Chaiwatthanaram in
Ayutthaya Historical Park
Ayutthaya Historical Park ( th, อุทยานประวัติศาสตร์พระนครศรีอยุธยาPronunciation) covers the ruins of the old city of Ayutthaya, Phra Nakhon Si Ayutthaya Province, Thailand. Th ...
. Thai Prime Minister
Prayut Chan-o-cha
Prayut Chan-o-cha (sometimes spelled Prayuth Chan-ocha; th, ประยุทธ์ จันทร์โอชา, ; born 21 March 1954) is a Thai politician and retired army officer who has served as the Prime Minister of Thailand since he ...
visited the flood-stricken areas, especially
Sukhothai on an unknown day as a result. Six individuals in the area were killed by the floods and two more were missing.
Elsewhere
In
Laos, the National Disaster Management Organisastion (NDMO) reported that Dianmu affected several provinces in the country, although they are still continuing to assess the damages from the storm there as of September 28.
Notes
See also
*
Weather of 2021
The following is a list of weather events that occurred in 2021. The year began with La Niña conditions. There were several natural disasters around the world from various types of weather, including blizzards, cold waves, droughts, heat wave ...
*
Tropical cyclones in 2021
During 2021, tropical cyclones formed in seven major bodies of water, commonly known as tropical cyclone basins. Tropical cyclones will be assigned names by various weather agencies if they attain maximum sustained winds of . During the year, one ...
*
Tropical Storm Rai (2016)
Tropical Storm Rai was a weak and short-lived tropical cyclone which affected Indochina in September 2016. Formed from a tropical disturbance on September 11, the system developed into a tropical storm (on the JTWC scale) and reached its peak int ...
References
External links
JMA General Informationof Tropical Storm Dianmu (2115) from Digital Typhoon
JMA Best Track Dataof Tropical Storm Dianmu (2115)
JMA Best Track Data (Graphics)of Tropical Storm Dianmu (2115)
JTWC Best Track Dataof Tropical Storm 21W (Twenty-One)
21W.TWENTYONEfrom the U.S. Naval Research Laboratory
{{DEFAULTSORT:Dianmu (2021)
2021 Pacific typhoon season
Tropical cyclones in 2021
2021 in Vietnam
Typhoons in Vietnam
Western Pacific tropical storms