Typhoon Choi-wan (2009)
Encyclopedia
Typhoon Choi-wan was a powerful typhoon that became the first Category 5 equivalent typhoon to form during the 2009 Pacific typhoon season
. Forming on September 11, 2009, about 1100 km (700 mi) to the east of Guam
, the initial disturbance rapidly organized into a tropical depression. By September 12 ,the depression intensified into a tropical storm, at which time it was given the name Choi-wan. The following day, rapid intensification
took place through September 14. Choi-wan attained its peak intensity on September 15, as it moved through the Northern Mariana Islands
with the Japan Meteorological Agency reporting peak windspeeds of 195 km/h (120 mph 10-minute sustained). Additionally, the Joint Typhoon Warning Center reported the storm to have attained winds of 260 km/h (160 mph 1-minute sustained). The typhoon remained very powerful until September 17 when the storm's outflow
weakened. The typhoon underwent an eyewall replacement cyclone, leading to intensity fluctuations. By September 19, Choi-wan rapidly weakened as strong wind shear
caused convection
to diminish. The following day, the system transitioned into an extratropical cyclone
and dissipated several hours later over open waters.
Despite the intensity of Choi-wan when it passed through the Northern Mariana Islands, no casualties were reported. However, following the storm, the United States Navy
deemed that the island of Alamagan
was uninhabitable, with all but one of the structures completely destroyed and most of the islands' trees downed. In response to this, all residents on the island were evacuated to nearby Saipan.
(JTWC) began monitoring an area of convection
roughly 1,100 km (700 mi) east of Guam
. A broad, low-level circulation center
had formed within the system and became increasingly organized, showing signs of developing convective banding. A Tropical Cyclone Formation Alert
was released later that day as convection was rapidly consolidating around the low, which was embedded within the eastern end of the monsoon
al trough
. It was then declared as a tropical depression by the Japan Meteorological Agency
(JMA) and the JTWC with the latter designating it as Tropical Depression 15W The tropical depression was tracking westward along the southern edge of the subtropical
ridge
situated east of the international dateline.
During September 12, the depression continued to develop quickly with both the JMA and the JTWC reporting that the depression had intensified into a Tropical Storm later that day, with the JMA assigning the international name of Choi-wan and the international designation of 0915. During September 13, Choi-wan gradually developed whilst moving west with the JMA reporting that Choi-wan had become a severe tropical storm late that day, before reporting along with the JTWC early the next day that Choi-wan had intensified further and had become a weak Typhoon with multiple spiral bands that had wrapped into the fully consolidated center to form a banding eye. During September 14, Choi-wan intensified further whilst moving along the southwestern edge of a deep level subtropical ridge of the northeast, intensifying into a Category 4-equivalent typhoon on the Saffir-Simpson Hurricane Scale
with 1-minute winds of 220 km/h (140 mph).
Early on September 15, the JTWC reported that Typhoon Choi-wan had intensified further and had become a Category 4-equivalent Super Typhoon whilst passing over the island of Alamagan
. Later that day the JMA reported that Typhoon Choi-wan had reached its 10-minute peak wind speeds of 195 km/h (120 mph) and a pressure of 915 hPa (mbar). Typhoon Choi-wan then intensified further and reached its peak 1-minute wind speeds of 260 km/h (160 mph) which made it the first Category 5-equivalent tropical cyclone on the Saffir-Simpson Hurricane Scale
anywhere in the world in 2009.
With the help of excellent poleward outflow and high ocean heat content, Typhoon Choi-wan remained at its peak intensity until early on September 17 when deep convection started to erode in the northwestern quadrant as the tropical upper tropospheric trough
(TUTT) cell to the northwest was no longer providing good outflow. Choi-wan was then downgraded to a typhoon by the JTWC as it started to undergo an eyewall replacement cycle, with the JTWC reporting a secondary peak intensity of 150 km/h (90 mph), during the next day. During September 19, Choi-wan rapidly weakened, as it moved into an unfavorable environment with higher amounts of vertical wind shear, causing the storm's deep convection to erode. As a result of this and dry latitude air wrapping into the low level circulation center, the JTWC decided to downgrade Choi-wan to an extratropical system
and released their final advisory, early the next day before the JMA followed suit later that day. The JMA then reported that the extratropical low had dissipated completely, early on September 21.
Weather Forecast Office in Guam, using data from the JTWC, placed Tinian
and Saipan
under a Typhoon Watch whilst declaring a Tropical Storm Watch also declared for Guam and Rota
. By September 15, the islands of Agrihan, Tinian and Saipan before being upgraded to tropical storm warnings and a typhoon watch. Additionally, the watches in place for Guam and Rota were discontinued. These warnings were kept in force until late on September 14, when the warnings for Tinian were canceled and the typhoon watch for Saipan was canceled, while the typhoon watch was upgraded to a Typhoon Warning as Choi-wan rapidly intensified. The Tropical Storm Warning in place for Saipan was canceled during September 15 as Choi-wan intensified into a high-end Category 4 equivalent super typhoon. All watches and warnings were discontinued during the afternoon of September 16 once Choi-wan was no longer a threat to the Mariana Islands.
By September 15, shelters were opened throughout Tinian and Saipan at local schools, most schools and all governmental buildings were closed and residents rushed to board up their homes. The American Red Cross
had also mobilized on the islands by this time. Some private schools were open during the morning but let out early to allow students to return to their families before the typhoon's arrival. On Saipan, 179 residents sought refuge in shelters by the afternoon of September 15, by which time heavy rain had begun falling. Only one flight was delayed by the typhoon across all the islands. The youth basketball league in the Northern Mariana Islands canceled their games for the time Choi-wan passed through the islands. At the height of the storm, a total of 270 residents sought refuge in shelters on Saipan.
; however these were discontinued later that day. The JMA then placed the Yokohama, Moji and Naha under a Typhoon Warning early the next day. These warnings were kept in place until early on September 19, when the JMA added the Kushiro and Otaru to the warnings. However, the warnings were dropped for all areas except Yokohama and Kushiro as the typhoon turned away from Japan. These warnings stayed in effect until late the next day when they were cancelled as Choi-wan began to dissipate.
were downed trees which littered streets across the islands. Power lines were downed and sewer pipes were broken; however, crews began repairing damage once Choi-wan passed. In Garapan
, the major shelter on the island sustained minor damage and repair work on it would take roughly a week.
On Alamagan, residents attempted to contact officials on other islands on September 17. Despite the extreme intensity of the storm, all sixteen residents on the island, including the 4-day old infant were safe. During their attempted contact, the connection was poor and hard to understand. The following day, the United States Navy
sent a ship and helicopter to the island to assess the situation. The Navy stated that the entire island of Alamagan was a total loss, with all but one of the structures, a facility for laboratory and research, completely destroyed and most of the islands' trees downed.
Once on the island, they determined that all residents needed to be evacuated "...whether they like or not". The first to be evacuated from the island were the infant and six people in the family; the infant was taken to a hospital on Saipan as a precaution. On nearby Agrihan, it was determined that the residents on the island also needed to be evacuated. Prior to their evacuations, they were given relief supplies, mainly food and water, to survive for five days. Roughly 260 gallons of fresh water, 50 lbs of rice and other health or comfort supplies were delivered by Helicopter Sea Combat Squadron 25 to both islands. On September 21, the Salvation Army
announced that residents displaced by the storm would be received donated items, such as clothing, toys, pillows and baby formula.
2009 Pacific typhoon season
The 2009 Pacific typhoon season was the period that tropical cyclones formed in the Western Pacific Ocean. The season ran throughout the year during 2009, with most tropical cyclones forming between May and November. The scope of this article is limited to the Pacific Ocean, north of the equator...
. Forming on September 11, 2009, about 1100 km (700 mi) to the east of Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
, the initial disturbance rapidly organized into a tropical depression. By September 12 ,the depression intensified into a tropical storm, at which time it was given the name Choi-wan. The following day, rapid intensification
Rapid deepening
Rapid deepening, also known as rapid intensification, is a meteorological condition that occurs when the minimum sea-level atmospheric pressure of a tropical cyclone decreases drastically in a short period of time. The National Weather Service describes rapid deepening as a decrease of...
took place through September 14. Choi-wan attained its peak intensity on September 15, as it moved through the Northern Mariana Islands
Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands , is a commonwealth in political union with the United States, occupying a strategic region of the western Pacific Ocean. It consists of 15 islands about three-quarters of the way from Hawaii to the Philippines...
with the Japan Meteorological Agency reporting peak windspeeds of 195 km/h (120 mph 10-minute sustained). Additionally, the Joint Typhoon Warning Center reported the storm to have attained winds of 260 km/h (160 mph 1-minute sustained). The typhoon remained very powerful until September 17 when the storm's outflow
Outflow (meteorology)
Outflow, in meteorology, is air that flows outwards from a storm system. It is associated with ridging, or anticyclonic flow. In the low levels of the troposphere, outflow radiates from thunderstorms in the form of a wedge of rain-cooled air, which is visible as a thin rope-like cloud on weather...
weakened. The typhoon underwent an eyewall replacement cyclone, leading to intensity fluctuations. By September 19, Choi-wan rapidly weakened as strong wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...
caused convection
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
to diminish. The following day, the system transitioned into an extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
and dissipated several hours later over open waters.
Despite the intensity of Choi-wan when it passed through the Northern Mariana Islands, no casualties were reported. However, following the storm, the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
deemed that the island of Alamagan
Alamagan
The Northern Marianas island of Alamagan is located north from Saipan and is 11.12 km² in area. The island's volcano has a large caldera at the summit. The volcano last erupted around 870 AD, with an error bar of 100 years. It involved pyroclastic flows, and had a VEI of 4...
was uninhabitable, with all but one of the structures completely destroyed and most of the islands' trees downed. In response to this, all residents on the island were evacuated to nearby Saipan.
Meteorological history
Early on September 11, the Joint Typhoon Warning CenterJoint Typhoon Warning Center
The Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at the Naval Maritime Forecast Center in Pearl Harbor, Hawaii...
(JTWC) began monitoring an area of convection
Atmospheric convection
Atmospheric convection is the result of a parcel-environment instability, or temperature difference, layer in the atmosphere. Different lapse rates within dry and moist air lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to...
roughly 1,100 km (700 mi) east of Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
. A broad, low-level circulation center
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...
had formed within the system and became increasingly organized, showing signs of developing convective banding. A Tropical Cyclone Formation Alert
Tropical Cyclone Formation Alert
A Tropical Cyclone Formation Alert is a bulletin released by the U.S. Navy-operated Joint Typhoon Warning Center in Honolulu, Hawaii or the Naval Maritime Forecast Center in Norfolk, Virginia, warning of the possibility of a tropical cyclone forming from a tropical disturbance that has been...
was released later that day as convection was rapidly consolidating around the low, which was embedded within the eastern end of the monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
al trough
Trough (meteorology)
A trough is an elongated region of relatively low atmospheric pressure, often associated with fronts.Unlike fronts, there is not a universal symbol for a trough on a weather chart. The weather charts in some countries or regions mark troughs by a line. In the United States, a trough may be marked...
. It was then declared as a tropical depression by the Japan Meteorological Agency
Japan Meteorological Agency
The or JMA, is the Japanese government's weather service. Charged with gathering and reporting weather data and forecasts in Japan, it is a semi-autonomous part of the Ministry of Land, Infrastructure and Transport...
(JMA) and the JTWC with the latter designating it as Tropical Depression 15W The tropical depression was tracking westward along the southern edge of the subtropical
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...
ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
situated east of the international dateline.
During September 12, the depression continued to develop quickly with both the JMA and the JTWC reporting that the depression had intensified into a Tropical Storm later that day, with the JMA assigning the international name of Choi-wan and the international designation of 0915. During September 13, Choi-wan gradually developed whilst moving west with the JMA reporting that Choi-wan had become a severe tropical storm late that day, before reporting along with the JTWC early the next day that Choi-wan had intensified further and had become a weak Typhoon with multiple spiral bands that had wrapped into the fully consolidated center to form a banding eye. During September 14, Choi-wan intensified further whilst moving along the southwestern edge of a deep level subtropical ridge of the northeast, intensifying into a Category 4-equivalent typhoon on the Saffir-Simpson Hurricane Scale
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...
with 1-minute winds of 220 km/h (140 mph).
Early on September 15, the JTWC reported that Typhoon Choi-wan had intensified further and had become a Category 4-equivalent Super Typhoon whilst passing over the island of Alamagan
Alamagan
The Northern Marianas island of Alamagan is located north from Saipan and is 11.12 km² in area. The island's volcano has a large caldera at the summit. The volcano last erupted around 870 AD, with an error bar of 100 years. It involved pyroclastic flows, and had a VEI of 4...
. Later that day the JMA reported that Typhoon Choi-wan had reached its 10-minute peak wind speeds of 195 km/h (120 mph) and a pressure of 915 hPa (mbar). Typhoon Choi-wan then intensified further and reached its peak 1-minute wind speeds of 260 km/h (160 mph) which made it the first Category 5-equivalent tropical cyclone on the Saffir-Simpson Hurricane Scale
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...
anywhere in the world in 2009.
With the help of excellent poleward outflow and high ocean heat content, Typhoon Choi-wan remained at its peak intensity until early on September 17 when deep convection started to erode in the northwestern quadrant as the tropical upper tropospheric trough
Tropical Upper Tropospheric Trough
A tropical upper tropospheric trough , also known as the mid-oceanic trough, is a trough situated in upper-level tropics. Its formation is usually caused by the intrusion of energy and wind from the mid-latitudes into the tropics. It can also develop from the inverted trough adjacent to an upper...
(TUTT) cell to the northwest was no longer providing good outflow. Choi-wan was then downgraded to a typhoon by the JTWC as it started to undergo an eyewall replacement cycle, with the JTWC reporting a secondary peak intensity of 150 km/h (90 mph), during the next day. During September 19, Choi-wan rapidly weakened, as it moved into an unfavorable environment with higher amounts of vertical wind shear, causing the storm's deep convection to erode. As a result of this and dry latitude air wrapping into the low level circulation center, the JTWC decided to downgrade Choi-wan to an extratropical system
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...
and released their final advisory, early the next day before the JMA followed suit later that day. The JMA then reported that the extratropical low had dissipated completely, early on September 21.
Mariana Islands
Early on September 12, the National Weather ServiceNational Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
Weather Forecast Office in Guam, using data from the JTWC, placed Tinian
Tinian
Tinian is one of the three principal islands of the Commonwealth of the Northern Mariana Islands.-Geography:Tinian is about 5 miles southwest of its sister island, Saipan, from which it is separated by the Saipan Channel. It has a land area of 39 sq.mi....
and Saipan
Saipan
Saipan is the largest island of the United States Commonwealth of the Northern Mariana Islands , a chain of 15 tropical islands belonging to the Marianas archipelago in the western Pacific Ocean with a total area of . The 2000 census population was 62,392...
under a Typhoon Watch whilst declaring a Tropical Storm Watch also declared for Guam and Rota
Rota (island)
Rota also known as the "peaceful island", is the southernmost island of the United States Commonwealth of the Northern Mariana Islands and the second southernmost of the Marianas Archipelago. It lies approximately 40 miles north-northeast of the United States territory of Guam...
. By September 15, the islands of Agrihan, Tinian and Saipan before being upgraded to tropical storm warnings and a typhoon watch. Additionally, the watches in place for Guam and Rota were discontinued. These warnings were kept in force until late on September 14, when the warnings for Tinian were canceled and the typhoon watch for Saipan was canceled, while the typhoon watch was upgraded to a Typhoon Warning as Choi-wan rapidly intensified. The Tropical Storm Warning in place for Saipan was canceled during September 15 as Choi-wan intensified into a high-end Category 4 equivalent super typhoon. All watches and warnings were discontinued during the afternoon of September 16 once Choi-wan was no longer a threat to the Mariana Islands.
By September 15, shelters were opened throughout Tinian and Saipan at local schools, most schools and all governmental buildings were closed and residents rushed to board up their homes. The American Red Cross
American Red Cross
The American Red Cross , also known as the American National Red Cross, is a volunteer-led, humanitarian organization that provides emergency assistance, disaster relief and education inside the United States. It is the designated U.S...
had also mobilized on the islands by this time. Some private schools were open during the morning but let out early to allow students to return to their families before the typhoon's arrival. On Saipan, 179 residents sought refuge in shelters by the afternoon of September 15, by which time heavy rain had begun falling. Only one flight was delayed by the typhoon across all the islands. The youth basketball league in the Northern Mariana Islands canceled their games for the time Choi-wan passed through the islands. At the height of the storm, a total of 270 residents sought refuge in shelters on Saipan.
Japan
Early on September 16 the JMA started to issue Typhoon force wind warnings, for the Naha, OkinawaNaha, Okinawa
is the capital city of the Japanese prefecture of Okinawa.Naha is a coastal city located on the East China Sea coast of the southern part of Okinawa Island, the largest of the Ryukyu Islands...
; however these were discontinued later that day. The JMA then placed the Yokohama, Moji and Naha under a Typhoon Warning early the next day. These warnings were kept in place until early on September 19, when the JMA added the Kushiro and Otaru to the warnings. However, the warnings were dropped for all areas except Yokohama and Kushiro as the typhoon turned away from Japan. These warnings stayed in effect until late the next day when they were cancelled as Choi-wan began to dissipate.
Impact and aftermath
On September 15, the eye of Choi-wan passed within 10 km (5 mi) of Alamagan and brought winds of up to 230 km/h (145 mph) to the island. The most recent storm of Choi-wan's intensity to strike the islands was Typhoon Chaba in 2004. That storm caused severe damage and widespread flooding. Unlike Chaba, relatively little rainfall fell due to Choi-wan, and no flooding was reported. The main effects from the typhoon in SaipanSaipan
Saipan is the largest island of the United States Commonwealth of the Northern Mariana Islands , a chain of 15 tropical islands belonging to the Marianas archipelago in the western Pacific Ocean with a total area of . The 2000 census population was 62,392...
were downed trees which littered streets across the islands. Power lines were downed and sewer pipes were broken; however, crews began repairing damage once Choi-wan passed. In Garapan
Garapan
Garapan is the largest village and the center of the tourism industry on the island of Saipan, which is a part of the United States Commonwealth of the Northern Mariana Islands ....
, the major shelter on the island sustained minor damage and repair work on it would take roughly a week.
On Alamagan, residents attempted to contact officials on other islands on September 17. Despite the extreme intensity of the storm, all sixteen residents on the island, including the 4-day old infant were safe. During their attempted contact, the connection was poor and hard to understand. The following day, the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
sent a ship and helicopter to the island to assess the situation. The Navy stated that the entire island of Alamagan was a total loss, with all but one of the structures, a facility for laboratory and research, completely destroyed and most of the islands' trees downed.
Once on the island, they determined that all residents needed to be evacuated "...whether they like or not". The first to be evacuated from the island were the infant and six people in the family; the infant was taken to a hospital on Saipan as a precaution. On nearby Agrihan, it was determined that the residents on the island also needed to be evacuated. Prior to their evacuations, they were given relief supplies, mainly food and water, to survive for five days. Roughly 260 gallons of fresh water, 50 lbs of rice and other health or comfort supplies were delivered by Helicopter Sea Combat Squadron 25 to both islands. On September 21, the Salvation Army
Salvation Army
The Salvation Army is a Protestant Christian church known for its thrift stores and charity work. It is an international movement that currently works in over a hundred countries....
announced that residents displaced by the storm would be received donated items, such as clothing, toys, pillows and baby formula.
See also
- 2009 Pacific typhoon season2009 Pacific typhoon seasonThe 2009 Pacific typhoon season was the period that tropical cyclones formed in the Western Pacific Ocean. The season ran throughout the year during 2009, with most tropical cyclones forming between May and November. The scope of this article is limited to the Pacific Ocean, north of the equator...
- Typhoon Chaba (2004)