Feature article

Tropical cyclone guidance for the 2006–07 season

Weak to moderate El Niño conditions are likely to increase the chances of tropical cyclone activity for several tropical South Pacific countries over coming months.

Figure 1. Tropical Cylone intensity in the South West Pacific

For the coming tropical cyclone season, from November 2006 – May 2007, we are likely to see above average numbers of tropical cyclones in several parts of the South Pacific near and east of the Date Line. Countries with increased risk over this period include Fiji, Wallis and Futuna, Tonga, Niue, and the southern Cook Islands. Islands west of the Date Line are still likely to experience tropical cyclones, with a normal rate of occurrence.

Tropical sea surface temperatures, which play an important role in the development of tropical cyclones, are presently above average along the equator across the entire Pacific Basin. Climate forecasting organisations in the Pacific are in general agreement that we are seeing the development of a weak to moderate El Niño, although the situation is still evolving. This brings above normal risk of tropical cyclones near and east of the Date Line. There is a good chance that the first tropical cyclone of the coming season in the South Pacific region may occur before the end of November, about a month earlier than is normal in either a neutral or La Niña seasons. About ten tropical cyclones on average can be expected over the entire Southwest Pacific region during a weak El Niño season.

In the Southwest Pacific, tropical cyclones usually develop in the wet season, from November through April, but occasionally occur in May. Peak cyclone occurrence is usually from January to March. In seasons similar to the present, several tropical cyclones usually occur in the region between Vanuatu and Niue with some affecting other areas. About half of the tropical cyclones that develop reach hurricane force with mean wind speeds at least 64 knots (118 km/h).

Southwest Pacific tropical cyclones are grouped into classes ranging from 1 to 5, with 5 being the strongest. On average four per season reach at least class 4 with mean wind speeds of at least 64 knots or 118 km/h, while two usually reach class 5 with mean speeds in excess of 90 knots or 167 km/h. Last season (2005/06) in the South Pacific, Cyclones Larry and Monica were particularly severe, both reaching class 5 in strength. These were especially destructive to coastal and some populated environments in Queensland and the Northern Territory of Australia. Three class 4 tropical cyclones occurred further east, but these missed populated areas.

Country Average over
all years
Average over
Weak ENSO years
Fiji 2.3 2.4 - 2.8 Increased risk
Tonga 2.0 2.3 - 2.7 Increased risk
Niue 1.8 2.2 - 2.6 Increased risk
Wallis and Futuna 1.8 2.1 - 2.6 Increased risk
Southern Cook Islands 1.6 1.8 - 2.2 Increased risk
Samoa 1.5 1.5 - 1.9 Average - increased risk
Tuvalu 1.1 1.1 - 1.5 Average - increased risk
Solomon Islands 1.4 1.2 - 1.6 Average risk
Northern New Zealand 0.9 0.7 - 0.9 Average risk
Northern Cook Islands 0.8 0.7 - 0.9 Average risk
Austral Islands 0.8 0.8 - 1.0 Average risk
Society Islands 0.8 0.6 - 0.8 Average risk
Tokelau 0.8 0.6 - 0.8 Average risk
Papua New Guinea 0.6 0.4 - 0.6 Average risk
Tuamotu Islands 0.4 0.1 - 0.2 Average risk
Pitcairn Island 0.3 0.1 - 0.2 Average risk
Vanuatu 3.0 2.0 - 2.6 Variable risk - uncertain
New Caledonia 2.7 1.8 - 2.4 Variable risk - uncertain
Marquesas Islands 0.1 0.0 - 0.1 Cyclones unlikely
Western Kiribati 0.0 0.0 Cyclones unlikely
Eastern Kiribati 0.0 0.0 Cyclones unlikely

For further information:
Contact your local Meteorological Service