Cyclone Vaianu (2006)
Encyclopedia
Severe Tropical Cyclone Vaianu (RSMC Nadi designation: 12F, JTWC designation: 11P) was the fourth named tropical cyclone
of the 2005–06 South Pacific cyclone season. The system formed on February 11, and moved generally towards the south throughout its life. Vaianu ultimately peaked with winds corresponding to Category 1 status on the Saffir-Simpson Hurricane Scale
, and passed between Fiji
and Tonga
. Moving into cooler waters, the storm dissipated on February 16. Although the cyclone avoided land for the most part, it caused heavy rainfall and gusty winds in portions of Tonga. Flooding hit the capital city of Nuku'alofa
, and on some islands, the storm destroyed crops.
(RSMC) in Nadi, Fiji reported that Tropical Depression 12F had developed within a convergence zone which was located about 140 km (87 mi) to the northeast of Vanua Levu
. The depression tracked southeastward, although further development was initially inhibited by wind shear
. During the next day, the depression turned towards the southeast and moved into a more favorable environment for intensification. It was then designated as Tropical Depression 11P at 1800 UTC by the Joint Typhoon Warning Center
(JTWC). On February 11, the system significantly organized, and at 1200 UTC that day, RSMC Nadi reported that the depression had intensified into a Category 1 tropical cyclone on the Australian tropical cyclone intensity scale; it was assigned the name Vaianu.
At the time of being upgraded to a cyclone, Vaianu was situated about 190 km (118.1 mi) to the northwest of Vavaʻu, a Tonga
island chain. The storm turned southwestward under the steering currents of a ridge
to the southeast. The JTWC recognized the system as a tropical storm on February 12, and upgraded it into a tropical cyclone shortly thereafter. Vaianu continued to strengthen, and passed west of Tonga. The JTWC reported that the cyclone peaked in intensity at 1200 UTC on February 13, with maximum sustained 1-minute winds of 140 km/h (85 mph). RSMC Nadi assessed the storm as having peaked slightly later, with 10-minute winds of 130 km/h (80 mph), which made it a Category 3 severe tropical cyclone.
The storm held its strength for some time as it moved southward between Ono-i-Lau
and Tongatapu
. Beginning to accelerate, Vaianu entered the area of responsibility of the Tropical Cyclone Warning Centre in Wellington, New Zealand
. It curved southeastward and slowly deteroirated due to increasing wind shear and colder sea surface temperatures. The JTWC downgraded it to a tropical storm on February 15, and by the next day it was undergoing an extratropical transition
. At 0600 UTC, the JTWC classified it as extratropical, but it remained a powerful storm system for several days as it tracked over the open ocean.
and Niuatoputapu
under a tropical cyclone alert, before early the next day extending the alert to the whole of Tonga. Later that day the Vavau, Haapai, and Nomuka
islands were placed under a gale warning. The warnings stayed in force until late on February 12 when the gale warning was canceled, and concurrently, southern Tonga was placed under a tropical cyclone warning. These warnings were canceled on February 14. During the cyclone, RSMC Nadi placed the Lau Islands
under a strong wind warning, and a damaging swell warning was declared for Fiji
. Businesses in Nuku'alofa
closed as the storm passed by.
At the Fuaʻamotu station, sustained winds blew at 68 km/h (42.3 mph) during the worst of the storm, with gusts reaching 100 km/h (62.1 mph). Barometric pressure there fell to 995 millibars at 1400 UTC on February 13, and 97.7 mm (3.8 in) of rain fell. Since the cyclone remained predominately over water, its effects were limited. Nonetheless, portions of Tongan experienced torrential rainfall and high winds. On Tongatapu and Eua, the storm inflicted extensive crop damage, and it is estimated that 70% of the banana crop was destroyed. While little property damage took place, the storm caused power outages across its path that took up a week to fully restore. In Nuku'alofa
, the capital of Tonga, flooding of low-lying areas reportedly shut down the city for two days. The high winds brought down trees and dispersed debris throughout the region, while schools were forced to close.
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 2005–06 South Pacific cyclone season. The system formed on February 11, and moved generally towards the south throughout its life. Vaianu ultimately peaked with winds corresponding to Category 1 status 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...
, and passed between Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
and Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
. Moving into cooler waters, the storm dissipated on February 16. Although the cyclone avoided land for the most part, it caused heavy rainfall and gusty winds in portions of Tonga. Flooding hit the capital city of Nuku'alofa
Nuku'alofa
Nukualofa is the capital of the Kingdom of Tonga. It is located on the north coast of the island of Tongatapu, in the southern most island group of Tonga.-Mythological origins:...
, and on some islands, the storm destroyed crops.
Meteorological history
Late on February 9, 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...
(RSMC) in Nadi, Fiji reported that Tropical Depression 12F had developed within a convergence zone which was located about 140 km (87 mi) to the northeast of Vanua Levu
Vanua Levu
Vanua Levu , formerly known as Sandalwood Island, is the second largest island of Fiji. Located 64 kilometres to the north of the larger Viti Levu, the island has an area of 5,587.1 km² and a population of some 130,000.- Geography :...
. The depression tracked southeastward, although further development was initially inhibited by 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...
. During the next day, the depression turned towards the southeast and moved into a more favorable environment for intensification. It was then designated as Tropical Depression 11P at 1800 UTC by 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). On February 11, the system significantly organized, and at 1200 UTC that day, RSMC Nadi reported that the depression had intensified into a Category 1 tropical cyclone on the Australian tropical cyclone intensity scale; it was assigned the name Vaianu.
At the time of being upgraded to a cyclone, Vaianu was situated about 190 km (118.1 mi) to the northwest of Vavaʻu, a Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
island chain. The storm turned southwestward under the steering currents of a ridge
Ridge (meteorology)
A ridge is an elongated region of relatively high atmospheric pressure, the opposite of a trough....
to the southeast. The JTWC recognized the system as a tropical storm on February 12, and upgraded it into a tropical cyclone shortly thereafter. Vaianu continued to strengthen, and passed west of Tonga. The JTWC reported that the cyclone peaked in intensity at 1200 UTC on February 13, with maximum sustained 1-minute winds of 140 km/h (85 mph). RSMC Nadi assessed the storm as having peaked slightly later, with 10-minute winds of 130 km/h (80 mph), which made it a Category 3 severe tropical cyclone.
The storm held its strength for some time as it moved southward between Ono-i-Lau
Ono-i-Lau
Ono-i-Lau is a volcanic and coral island in Fiji's Lau archipelago.One of the southernmost of the Lau Islands, it is located at 20.80° South and 178.75° East, and occupies an area of 7.9 square kilometers. It has a maximum elevation of 113 meters. It is 90 kilometers southsouthwest of Vatoa, the...
and Tongatapu
Tongatapu
Tongatapu is the main island of the Kingdom of Tonga and the location of its capital Nukualofa. It is located in Tonga's southern island group, to which it gives its name, and is the country's most populous island, with approximately 71,260 residents , 70.5% of the national population...
. Beginning to accelerate, Vaianu entered the area of responsibility of the Tropical Cyclone Warning Centre in Wellington, New Zealand
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...
. It curved southeastward and slowly deteroirated due to increasing wind shear and colder sea surface temperatures. The JTWC downgraded it to a tropical storm on February 15, and by the next day it was undergoing 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...
. At 0600 UTC, the JTWC classified it as extratropical, but it remained a powerful storm system for several days as it tracked over the open ocean.
Preparations and impact
Early on February 10, RSMC Nadi placed Niuafo'ouNiuafo'ou
Niuafoou is the most northerly island in the kingdom of Tonga. It is a volcanic rim island of 15 km² and with a population of 650 in 2006.-Geography:...
and Niuatoputapu
Niuatoputapu
For the 2009 tsunami, see the main article: 2009 Samoa tsunami.Niuatoputapu is an island in the island nation of Tonga, Pacific Ocean. Its name means sacred island. Older European names for the island are Traitors island or Keppel island.Niuatoputapu is located in the north of the country,...
under a tropical cyclone alert, before early the next day extending the alert to the whole of Tonga. Later that day the Vavau, Haapai, and Nomuka
Nomuka
Nomuka is a small island in the southern part of the Haapai group of islands in the Kingdom of Tonga. It is part of the Nomuka Group of islands, also called the Otu Muomua....
islands were placed under a gale warning. The warnings stayed in force until late on February 12 when the gale warning was canceled, and concurrently, southern Tonga was placed under a tropical cyclone warning. These warnings were canceled on February 14. During the cyclone, RSMC Nadi placed the Lau Islands
Lau Islands
The Lau Islands of Fiji are situated in the southern Pacific Ocean, just east of the Koro Sea. Of this chain of about one hundred islands and islets, about thirty are inhabited...
under a strong wind warning, and a damaging swell warning was declared for Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
. Businesses in Nuku'alofa
Nuku'alofa
Nukualofa is the capital of the Kingdom of Tonga. It is located on the north coast of the island of Tongatapu, in the southern most island group of Tonga.-Mythological origins:...
closed as the storm passed by.
At the Fuaʻamotu station, sustained winds blew at 68 km/h (42.3 mph) during the worst of the storm, with gusts reaching 100 km/h (62.1 mph). Barometric pressure there fell to 995 millibars at 1400 UTC on February 13, and 97.7 mm (3.8 in) of rain fell. Since the cyclone remained predominately over water, its effects were limited. Nonetheless, portions of Tongan experienced torrential rainfall and high winds. On Tongatapu and Eua, the storm inflicted extensive crop damage, and it is estimated that 70% of the banana crop was destroyed. While little property damage took place, the storm caused power outages across its path that took up a week to fully restore. In Nuku'alofa
Nuku'alofa
Nukualofa is the capital of the Kingdom of Tonga. It is located on the north coast of the island of Tongatapu, in the southern most island group of Tonga.-Mythological origins:...
, the capital of Tonga, flooding of low-lying areas reportedly shut down the city for two days. The high winds brought down trees and dispersed debris throughout the region, while schools were forced to close.