Feature Article

Fewer tropical cyclones are likely in the Pacific this year

For most South Pacific countries the chances of tropical cyclone activity are lower than normal for the November – January period

Many Pacific Island countries are likely to experience fewer than average tropical cyclones this season (see Table below). This pattern is expected because Southern Oscillation conditions affecting the tropical Pacific region are neutral, and are expected to remain so over the early part of the cyclone season. Countries with below average risk are: New Caledonia, Vanuatu, Fiji, Wallis and Futuna, Samoa, Tokelau, Niue and the Southern Cook Islands.

Tropical cyclones develop in the South Pacific over the wet season, usually from November through April. Peak cyclone occurrence is usually during January, February and March. On average, the highest numbers occur in the region around Vanuatu, New Caledonia, and the adjacent Coral Sea. In seasons similar to the present during November to January, at least one tropical cyclone usually occurs in that region. Taken over the whole of the South Pacific, on average four tropical cyclones can occur in the early part of the season, but this can range from as few as zero in 2000/01, to as many as eleven in 1997/98.

Tropical cyclones require huge amounts of energy to survive, and will form only over specific regions of the globe�s tropical oceans, where conditions are right for their formation and development. The La Ni�a and El Ni�o phenomena alter the patterns of climate, altering the risk of a cyclone in different parts of the South Pacific.

Tropical cyclone risk, neutral November-January periods, 1970–2000
Average number of tropical cyclones

Major tropical cyclones bring extremes of wind, rainfall and sea surges, resulting in river and coastal flooding, landslides, and extensive damage to crops, trees, houses, power lines, ports and roads. Many lives can be lost. For a small South Pacific island country the whole economy can be severely affected. Individual tropical cyclones are, however, rather unpredictable; so most South Pacific islands are exposed to some degree of risk every year and must be always prepared.

The December issue of the ICU will provide an update on information relating to any occurrences and further probability of tropical cyclones in our forecast region of the South West Pacific over the remainder of the wet season.

The following table shows the average number of tropical cyclones passing near the main island groups of the South Pacific over the November through January period.

(Based on 30 years of data, and for tropical cyclones having mean wind speeds over 34 knots*)

Area Average over all years Average over Neutral ENSO years Comment
Southern Papua-New Guinea 0.1 0.2 Average risk
Solomon Islands 0.5 0.4 Average risk
Tuvalu 0.7 0.5 Average risk
Tonga 0.9 0.7 Average risk
New Caledonia 1.4 1.1 Less than average
Vanuatu 1.6 1.1 Less than average
Fiji 1.2 0.9 Less than average
Wallis and Futuna 0.9 0.5 Less than average
Samoa 0.8 0.3 Less than average
Tokelau 0.5 0.2 Less than average
Niue 0.9 0.6 Less than average
Southern Cook Islands 0.8 0.5 Less than average
Northern Cook Islands 0.4 Less than 0.1 Cyclones unlikely
Society Islands/Tahiti 0.3 0.1 Cyclones unlikely
Austral Islands 0.3 0.1 Cyclones unlikely
Northern New Zealand 0.4 Less than 0.1 Cyclones unlikely

*For the southwest Pacific, “tropical cyclone” is a tropical low-pressure system intense enough to produce sustained gale force winds (at least 34 knots or 63 km/h). A “severe tropical cyclone” produces sustained hurricane force winds (at least 64 knots or 118 km/h), and corresponds to the hurricanes or typhoons of other parts of the world.

In the French language, the term “Cyclone tropicaux” refers to the hurricane phase (64 knots or 118 km per hour or more) but the Island Climate Update publication follows the English language definition of “Tropical cyclone” as defined in the World Meteorological Organisation Tropical Cyclone Operational Plan for the South Pacific and South-East Indian Ocean as follows “A non-frontal cyclone of synoptic scale developing over tropical waters and having a definite organised wind circulation with maximum 10-minute average wind speed of 34 knots (63 km per hour) or greater”.