TROPICAL CYCLONE ACTIVITY

First Quarter 2007 Summary

The 2006-2007 tropical cyclone season in the Southern Hemisphere has been somewhat lackluster, with generally below normal numbers in most categories (e.g., number of tropical cyclones and number of hurricanes in the South Pacific). In an average year, there are 28 tropical cyclones numbered by the JTWC in all of the South Pacific and South Indian Ocean . During the period July 2006 through late April 2007, there have been 24 cyclones numbered by the JTWC, of which 22 were given names by the respective RSMC. Of these 24, ten occurred in the South Pacific while 14 occurred in the South Indian Ocean .

Only four tropical cyclones (Zita, Arthur, TC 11P, and Becky,) formed in the South Pacific during the 1 st quarter of 2007, and (contrary to expectations) none of them affected American Samoa . Zita, the first south Pacific storm of 2007, formed west-northwest of Tahiti on January 22nd and quickly dissipated. Much like Zita, Arthur formed west of Tahiti on January 25th, and rapidly began to weaken after only 2 days at tropical storm strength. TC 11P formed north of Fiji on February 2nd, and tracked over Fiji ’s north island (Vanua Levu) and then south of Tonga before weakening around February 6th. Finally, Becky formed northwest of Vanuatu on March 26th, and dissipated off the coast of New Caledonia around March 29th.

Tropical cyclone activity in the western North Pacific basin was quiet during the first quarter of 2007, with only one numbered cyclone that formed at the end of March. This time of year is normally quiet, with only one or two numbered tropical cyclones in a typical year. In recent years, however, there have been some notable tropical cyclones during this normally quiet time of the year, including Typhoon Mitag (March 2002) and Typhoon Sudal (April 2004). The numbers of tropical cyclones in the western North Pacific basin increases through April, May and June, with the normal numbers for those months standing at 0.8, 1.3, and 2.2 respectively. The number of early season tropical cyclones in the western North Pacific is strongly related to El Niño, with more storms occurring during the onset of El Niño and fewer of them occurring during the year that follows El Niño.