South Pacific tropical cyclone season

A South Pacific tropical cyclone (Commonly referred to as hurricanes) is a non frontal, low pressure system that has developed, within an environment of warm sea surface temperatures and little vertical wind shear aloft in the South Pacific Ocean. Within the Southern Hemisphere there are officially three areas where tropical cyclones develop on a regular basis, these areas are the South-West Indian Ocean between Africa and 90°E, the Australian region between 90°E and 160°E and the South Pacific basin between 160°E and 120°W. The South Pacific basin between 160°E and 120°W is officially monitored by the Fiji Meteorological Service and New Zealand's MetService, while others like the Australian Bureau of Meteorology and the United States National Oceanic and Atmospheric Administration also monitor the basin. Each tropical cyclone year within this basin starts on July 1 and runs throughout the year, encompassing the tropical cyclone season which runs from November 1 and lasts until April 30 each season. Within the basin, most tropical cyclones have their origins within the South Pacific Convergence Zone or within the Northern Australian monsoon trough, both of which form an extensive area of cloudiness and are dominant features of the season. Within this region a tropical disturbance is classified as a tropical cyclone, when it has 10-minute sustained wind speeds of more than 65 km/h (35 mph), that wrap halfway around the low level circulation centre, while a severe tropical cyclone is classified when the maximum 10-minute sustained wind speeds are greater than 120 km/h (75 mph).

The ancient mariners of the South Seas who roamed the tropical Pacific before the arrival of the Europeans, knew of and feared the hurricanes of the South Pacific. They were keen and accurate observers of nature with traditional myths and legends, reflecting their knowledge of these systems. On his voyages around the Pacific, it is thought that Captain James Cook, did not collect any information about cyclones in the Pacific. The European whalers, traders and missionaries that followed Cook soon realised that the South Pacific, was not free of hurricanes and were the first to publish accounts about the systems. During 1853, Thomas Dobson subsequently became the first person to collect information about these systems, in order to attempt to understand and explain the characteristics of 24 tropical cyclones. However, these descriptions were vague and were of little value, because he only had a small amount of data and no synoptic weather charts. Over the next 40 years various reports, journals and log books on the storms were published, before E Knipping consolidated these reports and extended Dobson's list out to 120 tropical cyclones during 1893. During the 1920s Stephen Sargent Visher did some research into tropical cyclones in the Pacific and visited several island nations; including Fiji, Japan and the Philippines to obtain information on potential systems. He also consulted various journals and reports as well as Dobson's and Knipping's work, before he authored a number of papers on tropical cyclones in the Pacific. These papers contained information about 259 tropical storms in the South Pacific between 160°E and 140°W, two of which occurred during 1789 and 1819, while the rest occurred between 1830 and 1923. Visher also tried to estimate how many systems were occurring on an annual basis in each area, but over compensated for his incomplete records and came up with a figure of 12 severe tropical cyclones per year.

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