The 1991–92 South Pacific cyclone season was an above average tropical cyclone season, with eleven tropical cyclones occurring within the South Pacific basin between 160°E and 120°W. The first tropical cyclone of the season was first noted on November 13, 1991, while the last tropical cyclone dissipated on May 2, 1992. During the season at least 21 people were killed by tropical cyclones, while Tropical Cyclones Cliff and Innis were the only tropical cyclones not to cause any damage to any country in the Southern Pacific.
During the season, tropical cyclones were monitored by the Tropical Cyclone Warning Centers (TCWC) in Nadi, Fiji, and in Wellington, New Zealand.The FMS, or RSMC Nadi, warns on systems in the South Pacific located from the Equator to 25°S and from 160°E to 120°W. The New Zealand MetService, or TCWC Wellington, warns on systems from 25°S to 40°S and from 160°E to 120°W Whilst tropical cyclones that moved or formed to the west of 160°E were monitored as a part of the Australian region by the Australian Bureau of Meteorology. Both the United States Joint Typhoon Warning Center (JTWC) and the Naval Western Oceanography Center (NWOC) issued unofficial warnings within the southern Pacific. The JTWC issued warnings between 160°E and the International Date Line whilst the NWOC issued warnings for tropical cyclones forming between the International Date Line and the coasts of the Americas. Both the JTWC and the NWOC designated tropical cyclones with a number and a P suffix with numbers assigned in order to tropical cyclones developing within the whole of the South Pacific. The FMS and MetService both use the Australian Tropical Cyclone Intensity Scale, and measure windspeeds over a period of ten minutes, while the JTWC and the NWOC measured sustained winds over a period of one minute which are compared to the Saffir–Simpson hurricane wind scale.
Seasonal summary
During the season, a significant increase in the amount of tropical cyclones occurring within the South Pacific basin was observed, with eleven tropical cyclones occurring within the basin during the season compared to three during the previous season. This increase was attributed to a mature El Niño episode, that had started developing towards the end of the previous season. During the season the major areas of tropical cyclogenesis were shifted eastwards, from their mean position towards the more central parts of Pacific.
The first tropical cyclone of the season was first noted as a tropical depression on November 13, before it was named Tia during November 16, after it had become a category 1 tropical cyclone on the Australian tropical cyclone intensity scale. Over the next day the system rapidly intensified into a category 3 severe tropical cyclone and affected the Solomon Islands of Tikopia and Anuta while near its peak intensity. Tia subsequently started to weaken during November 19, as it became the first of six tropical cyclones to affect Vanuatu during the season.
After Severe Tropical Cyclone's Val and Wasa-Arthur, the South Pacific Convergence Zone gradually moved back to its near-normal position between the Samoan Islands, Southern Cook Islands and French Polynesia's Austral Islands.
The names: Tia, Val, Wasa, Betsy, Esau and Fran were later retired from the tropical cyclone naming lists. On July 1, 1992, the New Zealand Meteorological Service was split in two and became the Meteorological Service of New Zealand and the National Institute of Water and Atmospheric Research.
Systems Severe Tropical Cyclone Tia
On November 13, the FMS started to monitor a tropical depression that had developed within the South Pacific Convergence Zone, to the northeast of the Solomon Islands. Over the next few days, the system gradually developed further within an area of light winds in the upper troposphere, before the JTWC initiated advisories and designated it as Tropical Cyclone 03P early on November 15. During that day the system's upper-level outflow characteristics became more favourable for further development, before the FMS named the system Tia early the next day after it had developed into a Category 1 tropical cyclone. Later that day because of a developing northerly steering current, the system slowed down and undertook a small anticlockwise loop before starting to move towards the southwest and rapidly intensify. After rapidly intensifying throughout November 16 and 17, Tia passed within 55 km (35 mi) of Anuta Island at around 1800 UTC on November 17, before passing near Tikopia Island six hours later. As Tia moved near Tikopia, the FMS reported that the system had reached its peak intensity as a category 3 severe tropical cyclone with 10-minute sustained windspeeds of 140 km/h (85 mph). During November 18, Tia started to gradually weaken under the influence of cooler sea surface temperatures and strengthening vertical windshear, while it moved southwards under the influence of a strengthening upper level northerly wind flow. Over the next 24 hours, the system continued to move southwards and passed within of Vanuatu's Banks Islands, while gradually weakening further. Tia subsequently degenerated into a tropical depression during November 20, before it was last noted during the next day, as it crossed a part of its former track where it had been producing hurricane-force windspeeds a few days earlier.
Apart from extensive damage on the Solomon Islands of Anuta and Tikopia which directly lay in Tia's path, the overall effect of the cyclone was minimal. More than 1000 people were left homeless on Tikopia, after 90% of all dwellings were completely destroyed while the remaining 10% had either walls destroyed or roofs blown off. The cyclone also destroyed seven of the eight church buildings and all but one of the classroom buildings belonging to the two primary schools while food crops were completely destroyed with all coconut trees either blown down or uprooted. High seas and waves caused extensive damage to the coasts and flooded low-lying areas, salinating food crops such as taro and destroyed the water supply system on the island. As a result, Tikopia was declared a disaster area by the Solomon Islands National Disaster Council. Sustained windspeeds of , wind gusts of and a minimum pressure of were all reported by the automatic weather station on Anuta. Within Vanuatu the damage was mainly confined to fruit trees within the Banks and Torres Island Groups, while minor damage was reported to some old houses on Ambae, Epi and Tongoa Islands. On the Bank island of Mota, one man was slightly injured by flying corrugated iron while a church building was flattened.
Severe Tropical Cyclone Wasa–Arthur
On December 3, the FMS started to monitor a shallow tropical depression was embedded within a monsoon trough of low pressure over the Northern Cook Islands. Over the next couple of days, the system gradually developed further as it moved south-westwards, before the NWOC and the FMS reported that the depression had developed into Tropical Cyclone Wasa during December 5. After it had been named, Wasa slowed down and made a small cyclonic loop as it continued to intensify and became a category 3 severe tropical cyclone during December 7.
Early on December 8, the NWOC reported that Wasa had peaked with 1-minute sustained windspeeds of , which made it equivalent to a category 3 hurricane on the SSHWS. The next day, the FMS estimated peak 10-minute winds of 165 km/h (105 mph), making Wasa a Category 4 severe tropical cyclone. Over the next few days, the system weakened into a tropical depression after passing through the Society and Austral Islands. The NWOC issued their final advisory on Wasa on December 13, as the system turned northeastward to warmer waters. Later that day, Wasa became sufficiently organized to be reclassified as a category 1 tropical cyclone by the FMS, who renamed it Arthur. Over the next 24 hours, Arthur passed about north-northwest of Mururoa, which reported winds of . On December 14, the FMS reported that Wasa-Arthur had reached its secondary peak intensity of . The cyclone maintained this intensity while moving eastward through the uninhabited Acteon Group of islands and other atolls. On December 15, the NWOC classified it as Tropical Cyclone 08P, with peak 1-minute winds of . On December 16, the system gradually weakened into a shallow depression, and both the FMS and the NWOC issued their final advisories on Wasa-Arthur.
On December 9, ahead of Cyclone Wasa affecting French Polynesia, the High Commissioner Jean Montpezat declared a state of maximum alert which closed schools and banned navigation. On December 12, tourists on the island of Bora Bora were evacuated to a local church, after the system had swept high seas into tourist bungalows. Overall Cyclone Wasa-Arthur caused an estimated in damage within the six Leeward Islands, the two Windward Islands of Tahiti and Moorea and several of the Austral Islands with the majority of the damage done between December 9 – 12. The system destroyed 367 homes, damaged 855 other homes, destroyed or damaged a variety of crops and damaged several public buildings, hotels, roads and power installations, with the worst affected islands were Bora Bora and Tubuai. On Rurutu island, Moerai harbour was destroyed by a cyclonic swell generated by the system, while the local school and police station were destroyed by high waves. A woman and her child were killed while asleep after torrential rainfall from the system caused a mudslide on the island of Moorea, during a night of torrential rain the day after Wasa had made its closest approach to the island.
Severe Tropical Cyclone Val
Early on December 4, the FMS started to monitor a small tropical depression, that had developed along the Intertropical Convergence Zone just to the southeast of Tuvalu. During that day the system moved towards the northeast and steadily developed further with the FMS naming it Val early the next day, after it had become a category 1 tropical cyclone on the Australian tropical cyclone intensity scale. During that day the NWOC designated the system as Tropical Cyclone 06P and started to issue advisories, while Val started to move towards the south-southeast after the upper level north-westerly steering winds had increased. Over the next two days the system gradually intensified as it moved south-eastwards towards Western Samoa before the FMS reported late on December 7, that Val had peaked as a category 4 severe tropical cyclone with 10-minute sustained windspeeds of about 165 km/h (105 mph). The system subsequently made landfall later that day on the Western Samoan island of Savaii, before the NWOC reported that the cyclone had peaked with 1-minute sustained windspeeds of about 230 km/h (145 mph), which made it equivalent to a category 4 hurricane on the SSHS. After Val had passed over the island weakening upper-level winds and caused the system to slow down, before it started to move erratically and made a sharp clockwise loop which almost brought it over Savaii for a second time.
The cyclone lasted for five days in American Samoa and was designated by the United States Government as a major disaster on December 13, 1991. Western Samoa suffered more damage than American Samoa. The cyclone devastated the islands with winds and waves. The overall damages caused by Cyclone Val in American Samoa have been variously assessed. One estimate put the damages at $50 million in American Samoa and $200 million in Western Samoa due to damage to electrical, water, and telephone connections and destruction of various government buildings, schools, and houses.
Severe Tropical Cyclone Betsy