Tropical rainfall outlook: November 2006 to January 2007
Enhanced convection is likely in the equatorial region where rainfall is expected to be above average over Western and Eastern Kiribati, Tuvalu and Tokelau.
Near or above average rainfall is forecast for Samoa, the Northern Cook Islands, Wallis and Futuna, and Pitcairn Island.
Suppressed convection with below average rainfall is likely over Papua New Guinea, New Caledonia and the Marquesas Islands.
A large region of near or below average rainfall is likely from the Solomon Islands eastwards to Tuamotu Islands including, Vanuatu, Fiji, Tonga, Niue, and the Southern Cook Islands.
Near average rainfall is likely over the Society and Austral Islands.
The forecast model skill is moderate to high for this time of the year.
| Island group | Rainfall outlook | Outlook confidence |
|---|---|---|
| Western Kiribati | 15:30:45 (Above) | Moderate - high |
| Eastern Kiribati | 15:30:45 (Above) | Moderate - high |
| Tuvalu | 15:30:45 (Above) | Moderate - high |
| Tokelau | 15:30:45 (Average) | Moderate |
| Samoa | 20:40:40 (Near average or above) | Moderate |
| Northern Cook Islands | 20:40:40 (Near average or above) | Moderate |
| Wallis & Futuna | 20:40:40 (Near average or above) | Moderate |
| Pitcairn Island | 20:40:40 (Near average or above) | Moderate |
| Society Islands | 30:40:30 (Near average) | Moderate |
| Austral Islands | 25:45:30 (Near average) | Moderate - high |
| Solomon Islands | 40:40:20 (Near average or below) | Moderate - high |
| Vanuatu | 45:40:15 (Near average or below) | Moderate - high |
| Fiji | 40:40:20 (Near average or below) | Moderate - high |
| Tonga | 40:40:20 (Near average or below) | Moderate - high |
| Niue | 40:40:20 (Near average or below) | Moderate |
| Southern Cook Islands | 40:40:20 (Near average or below) | Moderate |
| Tuamotu Islands | 40:40:20 (Near average or below) | Moderate |
| Papua New Guinea | 50:30:20 (Below) | Moderate - high |
| New Caledonia | 50:35:15 (Below) | Moderate – high |
| Marquesas Islands | 45:30:25 (Below) | Moderate – high |
NOTE: Rainfall estimates for Pacific Islands for the next three months are given in the table. The tercile probabilities (e.g., 20:30:50) are derived from the interpretation of several global climate models. They correspond to the odds of the observed rainfall being in the lowest (driest) one third of the rainfall distribution, the middle one third, or the highest (wettest) one third of the distribution. On the long-term average, rainfall is equally likely (33% chance) in any tercile.
Forecast validation: August to October 2006
Enhanced convection with above average rainfall was expected over the Solomon Islands, with near or above average rainfall in Vanuatu. Average or above average rainfall was also expected from Wallis and Futuna to Pitcairn Island, including, Tonga, Niue, the Southern Cook Islands, the Society Islands, and the Austral Islands. Suppressed convection with below average rainfall was forecast for Tuvalu and Tokelau, with near or below average rainfall expected in the Tuamotu and Marquesas Islands. Near average rainfall was expected elsewhere.
A large region of enhanced convection and/or above average rainfall affected the region between the Solomon Islands and Western Kiribati, extending to Vanuatu and parts of Fiji. Rainfall was also above average over central French Polynesia. Convection was suppressed over Australia and much of the Tasman Sea, with below average rainfall over parts of New Caledonia. Rainfall was higher than expected in Tuvalu and Tokleau. The ‘hit’ rate for the August-October 2006 outlook was about 75%.
Tropical cyclones
Xavier, the first tropical cyclone of the season occurred on 22 October east of the Solomon Islands, and then tracked southeast to dissipate over the seas between Vanuatu and Fiji after 25 October. Estimated maximum sustained wind speeds reached 213 km/h, which is category 4 on the Saffir-Simpson scale. This was the earliest start to the season since 1997. An early start to the tropical cyclone season was signalled this year, due to the El Niño conditions.
The chances of tropical cyclone activity, for the November through May period, remains higher than normal for several South Pacific Islands near and east of the Date Line, while Islands west of the Date Line are still likely to experience normal rates of occurrence. Future issues of the ICU will provide updates on information relating to further occurrences of tropical cyclones in the region.