3.8.3.5 Australia and the South Pacific

The tropical cyclone season in the South Pacific-Australia region typically extends over the period November through April, with peak activity from December through March. Tropical cyclone activity in the Australian region (105°E–160°E) apparently declined somewhat over the past decade (Figure 3.40), although this may be partly due to improved analysis and discrimination of weak cyclones that previously were estimated at minimum tropical storm strength (Plummer et al., 1999). Increased cyclone activity in the Australian region has been associated with La Niña years, while below-normal activity has occurred during El Niño years (Plummer et al., 1999; Kuleshov and de Hoedt, 2003). In contrast, in the South Pacific east of 160°E, the opposite signal has been observed, and the most active years have been associated with El Niño events, especially during the strong 1982–1983 and 1997–1998 events (Levinson, 2005), and maximum ACE values occurred from January through March 1998 (Figure 3.40). Webster et al. (2005) found more than a doubling in the numbers of category 4 and 5 hurricanes in the southwest Pacific region between 1975 to 1989 and 1990 to 2004. In the 2005–2006 season, La Niña influences shifted tropical storm activity away from the South Pacific to the Australian region and in March and April 2006, four category 5 typhoons (Floyd, Glenda, Larry and Monica) occurred.