E. Linacre and B. Geerts
The record of tropical cyclones annually in the southwest Pacific (1) indicates an average of about 8 per cyclone season. An example showing the 1997 tropical cyclone tracks is shown in Fig 1. The actual number of cyclones varies, ranging from 2 to 16/a over 74 years. There is some indication of an increase from about 1970 onwards, but that probably reflects the more complete record possible once satellite pictures became available. There was no discernible increase in their number during the last 30 years, though perhaps an increase in their average intensity. There tend to be a statistically significant increase in the annual number when there was either a strong El Niño or a strong La Niña event, particularly the latter.
During El Niño years, more tropical cyclones occur in the central southern Pacific (Fig 13.5 in textbook).
Fig 1. Summary of tropical cyclone tracks in the Australian region in 1997. (Source: website, by Thomas R. Metcalf)
(1) Anon 1996. Natural Hazards Quarterly (Macquarie University, Sydney) 2, 4.