Higher risk of tropical cyclones in the Pacific east of the date line
For some South Pacific countries east of the date line the chances of tropical cyclone activity are higher than normal for the November 2002–January 2003 period, according to NIWA climate scientist Dr Jim Salinger.
“Pacific Island countries with increased risk over this period are Wallis and Futuna, Samoa, Tokelau, Niue and the southern Cook Islands” he said. “Tropical cyclones are still very likely about and west of the date line, but a lower than normal frequency of occurrence is expected.”
The last few tropical cyclone seasons were relatively “quiet”, with only six occurrences during 2000/01 and five in 2001/02. However, this season some Pacific Island countries east of the date line are likely to experience a higher risk of tropical cyclones than is usual. This eastward elongation of the normal pattern is expected because of now well-established moderate El Niño conditions presently affecting the tropical Pacific region.
Dr Salinger said “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 (the last El Niño).
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 Niña and El Niño phenomena alter the patterns of climate, altering the risk of a cyclone in different parts of the South Pacific.
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.
For further information:
In Pacific islands – contact your local Meteorological Service.
Average number of tropical cyclones occurring within 100 km square for the main island groups of the South Pacific for November–January (based on 31 years of data, and for tropical cyclones having winds over 34 knots*).
| Area | Average over all years | Average over Weak to Moderate ENSO Years | Comment |
|---|---|---|---|
| Wallis and Futuna | 0.9 | 1.4 | Increased risk |
| Samoa | 0.8 | 1.2 | Increased risk |
| Tokelau | 0.5 | 0.8 | Increased risk |
| Niue | 0.9 | 1.2 | Increased risk |
| Southern Cook Islands | 0.7 | 1.4 | Increased risk |
| New Caledonia | 1.4 | 1.1 | Reduced risk |
| Vanuatu | 1.6 | 1.1 | Reduced risk |
| Fiji | 1.1 | 0.8 | Reduced risk |
| Solomon Islands | 0.5 | 0.3 | Average risk |
| Tuvalu | 0.7 | 0.9 | Average risk |
| Tonga | 0.9 | 0.8 | Average risk |
| Northern Cook Islands | 0.4 | 0.4 | Average risk |
| Society Islands/Tahiti | 0.3 | 0.2 | Average risk |
| Northern Cook Islands | 0.4 | 0.4 | Average risk |
| Society Islands/Tahiti | 0.3 | 0.2 | Average risk |
| Austral Islands | 0.3 | 0.4 | Average risk |
| Northern New Zealand | 0.4 | 0.2 | Average risk |
| Southern Papua-New Guinea | 0.1 | Less than 0.1 | Cyclones unlikely |
| Tuamotu | 0.2 | Less than 0.1 | Cyclones unlikely |
| Pitcairn | 0.1 | 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”.
