The South Pacific and southeast Indian Ocean tropical cyclone season 1998-99

Twenty tropical cyclones formed in the South Pacific and southeast Indian Ocean region during the 1998 - 99 season. An uncharacteristic early start to the season saw the development of cyclone Zelia in early October followed by Alison in early November. But the season was most noted for the development of four category 5 systems developing off the west coast of Australia, with cyclone Vance making landfall as a category 5 system near the Western Australian town of Exmouth, In comparison, the Coral Sea experienced a very quiet and short-lived cyclone season with only three tropical cyclones developing in the region over a period of three weeks, Cyclone activity in the South Pacific was close to average. The 1998-99 season was characterised by weak La Nina conditions, with the Southern Oscillation Index (SOT) remaining moderately positive throughout and cool sea-surface and in particular subsurface temperatures dominating areas across the equatorial Pacific around 140 degreesW. The Intra Seasonal Oscillation (ISO), although demonstrating clear signals during late January to early February and again in March, lacked periodicity throughout the season.