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Cyclone Arthur (2007)
Encyclopedia
Cyclone Arthur was the eighth tropical depression and fourth tropical cyclone
of the 2006–07 South Pacific cyclone season. Forming as tropical depression on January 25, Arthur rapidly intensified
into a strong Category 2 cyclone on the Australian intensity scale according to the Regional Specialized Meteorological Centre
in Nadi, Fiji. The Joint Typhoon Warning Center
assessed the storm to have peaked as a minimal Category 1 cyclone. Shortly after peaking in intensity, the cyclone began to deteriorate due to unfavorable conditions. Quickly moving towards the east-southeast, the Arthur began to undergo an extratropical transition
. After turning towards the southeast, the center of circulation was almost fully exposed due to strong wind shear
. However, Arthur briefly re-strengthened late on January 26 before becoming extratropical the next day. Tropical Cyclone Arthur affected several small islands during its existence. French Polynesia
observed the most noteworthy effects from the storm, where several landslides damaged a few homes.
in Nadi, Fiji identified a tropical depression, which was given the number 08F, about 435 km (270 mi) west-northwest of Savai'i
island in Samoa
. The depression slowly traveled towards the east-southeast for several days as the overall structure of the storm fluctuated due to diurnal variations and strong wind shear
. Around 1700 UTC
on January 22, the Joint Typhoon Warning Center
(JTWC) issued a Tropical Cyclone Formation Alert
for the depression. The system developed a large banding feature
in the northern portion of the circulation and deep convection
formed around the center of circulation
. The depression had moved into an area of weak to moderate wind shear with favorable diffulence aloft. Later that day, gale warnings were issued for the northeastern quadrant of the system. Tropical Depression 08F continued to develop as an anticyclone
developed above the system, enhancing the environment around it. A mid-latitude trough
located north of the depression was steering it towards the east.
Early on January 24, the system became better organized and strengthened into a cyclone at 0600 UTC. The storm, which was named Arthur by the RSMC Nadi, began to undergo rapid intensification
as the structure improved significantly. Deep convection developed around the center with strong outflow towards the north. Several hours after becoming a cyclone, the JTWC issued their first advisory on Tropical Cyclone 09P as it traveled quickly towards the east-southeast. The quick movement was due to the influences of subtropical
ridge
to the north and a trough to the south. Later that day, a banding eye feature
began to develop as the storm intensified into a Category 2 cyclone on the Australian intensity scale. At 1800 UTC, the JTWC assessed Arthur to have reached its peak intensity with winds of 120 km/h (75 mph 1-minute winds), the equivalent of a minimal Category 1 hurricane on the Saffir-Simpson Hurricane Scale
. Early on January 25, Arthur reached its peak intensity with winds of 110 km/h (70 mph 10-minute winds) with a minimum pressure of 975 hPa
(mbar
) while located about 635 km (350 mi) north-northwest of Rarotonga
. Shortly after peaking in intensity, Arthur began to undergo an extratropical transition
and rapidly deteriorated due to strong wind shear.
The storm also began to merge with a low-level frontal boundary
associated with the remnants of Tropical Cyclone Zita. The strong shear left the center of circulation partially exposed, with deep convection persisting in only the southeastern quadrant. In addition to the shear, dry air began to enter the system, causing it to weaken further. While continuing to move at a quick pace, the storm began to turn towards the southeast along a baroclinic zone. Early on January 26, the JTWC issued their final advisory on the cyclone as it lost most of its tropical characteristics. Arthur re-intensified shortly after and the JTWC reissued advisories on the storm around 2100 UTC. The brief re-strengthening was the result of a breakdown in the baroclinic zone which allowed convection to redevelop around the center. Around the same time, Arthur left RSMC Nadi's area of responsibility (AoR) and entered the Tropical Cyclone Warning Centre Wellington
's AoR. The storm completed its extratropical transition around 1200 UTC on January 27, leading to the final advisory being issued on the storm.
was issued for Tutuila
, American Samoa
, Manu'a, and Swains Island
as Tropical Depression 08F approached the islands. Winds of up to 55 km/h (35 mph), with gusts up to 75 km/h (45 mph), were expected. Small craft advisories
were issued for the Cook Islands
due to large swells produced by the storm. All of the watches were cancelled late on January 23 as the depression was no longer forecast to impact the islands. On January 24, an Orange Alert was issued for the Austral Islands
. As the storm neared the region, the alert was upgraded to a Red Alert for Rurutu
and Tubuai
. Arthur produced minor damages in the Cook Islands—primarily consisting of beach erosion—on January 24. Heavy rains throughout French Polynesia
resulted in several landslides which damaged several homes on Tahiti
and Moorea
. Waves near the islands ranged from 1.5 to 2 m (4.9 to 6.5 ft). Winds in Tubuai reached 85 km/h (50 mph 10-minute winds) with gusts up to 115 km/h (71 mph). Several homes were damaged and roads were blocked by fallen trees throughout the island. Minor coastal flooding also occurred due to the large swells.
Since Cyclone Arthur caused little damage, the name was not retired and remains on "Naming List B" for the South Pacific basin.
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
of the 2006–07 South Pacific cyclone season. Forming as tropical depression on January 25, Arthur rapidly intensified
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...
into a strong Category 2 cyclone on the Australian intensity scale according to the Regional Specialized Meteorological Centre
Regional Specialized Meteorological Centre
A Regional Specialized Meteorological Centre is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as part of the World Weather Watch.-Tropical...
in Nadi, Fiji. The Joint Typhoon Warning Center
Joint 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...
assessed the storm to have peaked as a minimal Category 1 cyclone. Shortly after peaking in intensity, the cyclone began to deteriorate due to unfavorable conditions. Quickly moving towards the east-southeast, the Arthur began to undergo an extratropical transition
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...
. After turning towards the southeast, the center of circulation was almost fully exposed due to 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...
. However, Arthur briefly re-strengthened late on January 26 before becoming extratropical the next day. Tropical Cyclone Arthur affected several small islands during its existence. French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
observed the most noteworthy effects from the storm, where several landslides damaged a few homes.
Meteorological history
On January 21, 2007, the Regional Specialized Meteorological CentreRegional Specialized Meteorological Centre
A Regional Specialized Meteorological Centre is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as part of the World Weather Watch.-Tropical...
in Nadi, Fiji identified a tropical depression, which was given the number 08F, about 435 km (270 mi) west-northwest of Savai'i
Savai'i
Savaii is the largest and highest island in Samoa and the Samoa Islands chain. It is also the biggest landmass in Polynesia outside Hawaii and New Zealand. The island of Savai'i is also referred to by Samoans as Salafai, a classical Samoan term used in oratory and prose...
island in Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
. The depression slowly traveled towards the east-southeast for several days as the overall structure of the storm fluctuated due to diurnal variations and 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...
. Around 1700 UTC
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
on January 22, the Joint Typhoon Warning Center
Joint 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) issued 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...
for the depression. The system developed a large banding feature
Rainband
A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands can be stratiform or convective, and are generated by differences in temperature. When noted on weather radar imagery, this precipitation elongation is referred to as...
in the northern portion of the circulation and deep 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...
formed around the center of circulation
Eye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...
. The depression had moved into an area of weak to moderate wind shear with favorable diffulence aloft. Later that day, gale warnings were issued for the northeastern quadrant of the system. Tropical Depression 08F continued to develop as an anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
developed above the system, enhancing the environment around it. A mid-latitude 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...
located north of the depression was steering it towards the east.
Early on January 24, the system became better organized and strengthened into a cyclone at 0600 UTC. The storm, which was named Arthur by the RSMC Nadi, began to undergo 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...
as the structure improved significantly. Deep convection developed around the center with strong outflow towards the north. Several hours after becoming a cyclone, the JTWC issued their first advisory on Tropical Cyclone 09P as it traveled quickly towards the east-southeast. The quick movement was due to the influences of 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
High pressure area
A high-pressure area is a region where the atmospheric pressure at the surface of the planet is greater than its surrounding environment. Winds within high-pressure areas flow outward due to the higher density air near their center and friction with land...
to the north and a trough to the south. Later that day, a banding eye feature
Eye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...
began to develop as the storm intensified into a Category 2 cyclone on the Australian intensity scale. At 1800 UTC, the JTWC assessed Arthur to have reached its peak intensity with winds of 120 km/h (75 mph 1-minute winds), the equivalent of a minimal Category 1 hurricane 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...
. Early on January 25, Arthur reached its peak intensity with winds of 110 km/h (70 mph 10-minute winds) with a minimum pressure of 975 hPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
(mbar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
) while located about 635 km (350 mi) north-northwest of Rarotonga
Rarotonga
Rarotonga is the most populous island of the Cook Islands, with a population of 14,153 , out of the country's total population of 19,569.The Cook Islands' Parliament buildings and international airport are on Rarotonga...
. Shortly after peaking in intensity, Arthur began to undergo an extratropical transition
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 rapidly deteriorated due to strong wind shear.
The storm also began to merge with a low-level frontal boundary
Weather front
A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena. In surface weather analyses, fronts are depicted using various colored lines and symbols, depending on the type of front...
associated with the remnants of Tropical Cyclone Zita. The strong shear left the center of circulation partially exposed, with deep convection persisting in only the southeastern quadrant. In addition to the shear, dry air began to enter the system, causing it to weaken further. While continuing to move at a quick pace, the storm began to turn towards the southeast along a baroclinic zone. Early on January 26, the JTWC issued their final advisory on the cyclone as it lost most of its tropical characteristics. Arthur re-intensified shortly after and the JTWC reissued advisories on the storm around 2100 UTC. The brief re-strengthening was the result of a breakdown in the baroclinic zone which allowed convection to redevelop around the center. Around the same time, Arthur left RSMC Nadi's area of responsibility (AoR) and entered the Tropical Cyclone Warning Centre Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
's AoR. The storm completed its extratropical transition around 1200 UTC on January 27, leading to the final advisory being issued on the storm.
Preparations and impact
On January 21, a gale watchTropical cyclone warnings and watches
Warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate...
was issued for Tutuila
Tutuila
Tutuila is the largest and the main island of American Samoa in the archipelago of Samoan Islands. It is the third largest island in the Samoan Islands chain of the Central Pacific located roughly northeast of Brisbane, Australia and over northeast of Fiji. It contains a large, natural harbor,...
, American Samoa
American Samoa
American Samoa is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the sovereign state of Samoa...
, Manu'a, and Swains Island
Swains Island
Swains Island is an atoll in the Tokelau chain. Culturally a part of Tokelau, it is an unincorporated unorganized territory of the United States administered by American Samoa. Swains Island has also been known at various times as Olosenga Island, Olohega Island, Quiros Island, Gente Hermosa...
as Tropical Depression 08F approached the islands. Winds of up to 55 km/h (35 mph), with gusts up to 75 km/h (45 mph), were expected. Small craft advisories
Small craft advisory
A small craft advisory is a type of warning issued by the National Weather Service in the United States, most frequently in coastal areas. It is issued when winds have reached, or are expected to reach within 12 hours, a speed marginally less than gale force....
were issued for the Cook Islands
Cook Islands
The Cook Islands is a self-governing parliamentary democracy in the South Pacific Ocean in free association with New Zealand...
due to large swells produced by the storm. All of the watches were cancelled late on January 23 as the depression was no longer forecast to impact the islands. On January 24, an Orange Alert was issued for the Austral Islands
Austral Islands
The Austral Islands are the southernmost group of islands in French Polynesia, an overseas collectivity of France in the South Pacific. Geographically, they consist of two separate archipelagos, namely in the northwest the Tubuai Islands consisting of the Îles Maria, Rimatara, Rurutu, Tubuai...
. As the storm neared the region, the alert was upgraded to a Red Alert for Rurutu
Rurutu (Austral Islands)
Rurutu is the northernmost island in the Austral archipelago of French Polynesia, and the name of a commune consisting solely of that island. It is situated south of Tahiti....
and Tubuai
Tubuai (Austral Islands)
Tubuai is the name of a group of islands and also the name of its main island, being part of the Austral Islands, French Polynesia, in the Pacific Ocean. Tubuai, the main island of the Tubuai Island group, is located at . It is south of Tahiti...
. Arthur produced minor damages in the Cook Islands—primarily consisting of beach erosion—on January 24. Heavy rains throughout French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
resulted in several landslides which damaged several homes on Tahiti
Tahiti
Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...
and Moorea
Moorea
Moʻorea is a high island in French Polynesia, part of the Society Islands, 17 km northwest of Tahiti. Its position is . Moʻorea means "yellow lizard" in Tahitian...
. Waves near the islands ranged from 1.5 to 2 m (4.9 to 6.5 ft). Winds in Tubuai reached 85 km/h (50 mph 10-minute winds) with gusts up to 115 km/h (71 mph). Several homes were damaged and roads were blocked by fallen trees throughout the island. Minor coastal flooding also occurred due to the large swells.
Since Cyclone Arthur caused little damage, the name was not retired and remains on "Naming List B" for the South Pacific basin.